[Federal Register: July 3, 2001 (Volume 66, Number 128)]
[Proposed Rules]
[Page 35179-35193]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr03jy01-20]

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DEPARTMENT OF TRANSPORTATION

National Highway Traffic Safety Administration

49 CFR Part 575

[Docket No. NHTSA-2001-9663]


Consumer Information Regulations; Federal Motor Vehicle Safety
Standards; Rollover Resistance

AGENCY: National Highway Traffic Safety Administration (NHTSA), DOT.

ACTION: Request for comments.

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SUMMARY: This notice announces NHTSA's plans to evaluate a number of
driving maneuver tests for rollover resistance in accordance with the
requirements of the TREAD Act. The agency will develop a dynamic test
on rollovers of light motor vehicles for a consumer information
program, and seeks comments on the subject of dynamic rollover testing
and our approach to developing meaningful consumer information.

DATES: Comment Date: Comments must be received by August 17, 2001.

ADDRESSES: All comments should refer to Docket No. NHTSA-2001-9663 and
be submitted to: Docket Management, Room PL-401, 400 Seventh Street,
SW, Washington, D.C. 20590. Docket hours are 10 a.m. to 5 p.m. Monday
through Friday.
    For public comments and other information related to previous
notices on this subject, please refer to DOT Docket Nos. NHTSA-2000-
6859 and 8298 also available on the web at http:
//dms.gov/search, and NHTSA Docket No. 91-68; Notice 3, NHTSA Docket,
Room PL-403, 400 Seventh Street, SW, Washington, DC 20590. The NHTSA
Docket hours are from 9:30 am to 4 pm Monday through Friday.

FOR FURTHER INFORMATION CONTACT: For technical questions you may
contact Patrick Boyd, NPS-23, Office of Safety Performance Standards,
National Highway Traffic Safety Administration, 400 Seventh Street, SW,
Washington, DC 20590. Mr. Boyd can be reached by phone at (202) 366-
6346 or by facsimile at (202) 493-2739.

SUPPLEMENTARY INFORMATION:

    I. Safety Problem.

[[Page 35180]]

    II. Background.
    III. Preparatory Activity.
    IV. Difficulties Common to Various Dynamic Rollover Tests Using
Driving Maneuvers.
    V. Path-Following Driving Maneuver Tests.
    A. CU Double Lane Change.
    B. VDA Double Lane Change.
    C. Open-Loop Pseudo-Double Lane Change.
    D. Path-Corrected Limit Lane Change.
    VI. Open Loop Fishhook Maneuvers--Defined Steering Tests.
    VII. Dynamic Tests Other Than Driving Maneuvers.
    A. Centrifuge Test.
    B. Driving Maneuver Simulation.
    VIII. Solicitation of Comments.
    IX. Rulemaking Analyses and Notices.
    X. Submission of Comments.

I. Safety Problem

    Rollover crashes are complex events that reflect the interaction of
driver, road, vehicle, and environmental factors. We can describe the
relationship between these factors and the risk of rollover using
information from the agency's crash data programs. We limit our
discussion here to light vehicles, which consist of (1) passenger cars
and (2) multipurpose passenger vehicles and trucks under 4,536
kilograms (10,000 pounds) gross vehicle weight rating.\1\
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    \1\ For brevity, we use the term ``light trucks'' in this
document to refer to vans, minivans, sport utility vehicles (SUVs)
and pickup trucks, under 4,536 kilograms (10,000 pounds) gross
vehicle weight rating. NHTSA has also used the term ``LTVs'' to
refer to the same vehicles.
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    According to the 1999 Fatality Analysis Reporting System (FARS),
10,140 people were killed as occupants in light vehicle rollover
crashes, including 8,345 killed in single-vehicle rollover crashes.
Eighty percent of the people who died in single-vehicle rollover
crashes were not using a seat belt, and 64 percent were partially or
completely ejected from the vehicle (including 53 percent who were
completely ejected). FARS shows that 55 percent of light vehicle
occupant fatalities in single-vehicle crashes involved a rollover
event. The proportion differs greatly by vehicle type: 46 percent of
passenger car occupant fatalities in single-vehicle crashes involved a
rollover event, compared to 63 percent for pickup trucks, 60 percent
for vans, and 78 percent for sport utility vehicles (SUVs).
    Using data from the 1995-1999 National Automotive Sampling System
(NASS) Crashworthiness Data System (CDC), we estimate that 253,000
light vehicles were towed from a police-reported rollover crash each
year (on average), and that 27,000 occupants of these vehicles were
seriously injured (defined as an Abbreviated Injury Scale (AIS) rating
of at least AIS 3).\2\ Of these 253,000 light vehicle rollover crashes,
205,000 were the result of a single vehicle crash. (The present
rollover resistance ratings estimate the risk of rollover if a vehicle
is involved in a single vehicle crash.) Sixty-five percent of those
people who suffered a serious injury in single-vehicle tow-away
rollover crashes were not using a safety belt, and 50 percent were
partially or completely ejected (including 41 percent who were
completely ejected). Estimates from NASS-CDC indicate that 81 percent
of tow-away rollovers occurred in single-vehicle crashes, and that 87
percent (178,000) of the single-vehicle rollover crashes occurred after
the vehicle left the roadway. An audit of 1992-96 NASS-CDC data showed
that about 95 percent of rollovers in single vehicle crashes were
tripped by mechanisms such as curbs, soft soil, pot holes, guard rails,
and wheel rims digging into the pavement, rather than by tire/road
interface friction as in the case of untripped rollover events.
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    \2\ A broken hip is an example of an AIS 3 injury.
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    According to the 1995-1999 NASS-General Estimates System (GES)
data, 57,000 occupants annually received injuries rated as K or A on
the police KABCO injury scale in rollover crashes. (The police KABCO
scale calls ``A'' injuries ``incapacitating,'' but their actual
severity depends on local reporting practice. An ``incapacitating''
injury may mean that the injury was visible to the reporting officer or
that the officer called for medical assistance. A ``K'' injury is
fatal.) The data indicate that 205,000 single-vehicle rollover crashes
resulted in 46,000 K or A injuries. Fifty-four percent of those with K
or A injury in single-vehicle rollover crashes were not using a seat
belt, and 20 percent were partially or completely ejected from the
vehicle (including 18 percent who were completely ejected). Estimates
from NASS-GES indicate that 16 percent of light vehicles in police-
reported single-vehicle crashes rolled over. The estimated risk of
rollover differs by light vehicle type: 13 percent of cars and 14
percent of vans in police-reported single-vehicle crashes rolled over,
compared to 24 percent of pickup trucks and 32 percent of SUVs. The
percent of all police reported crashes for each vehicle type that
resulted in rollover was 1.6 percent for cars, 2.0 percent for vans,
3.7 percent for pickup trucks and 5.1 percent for SUVs as estimated by
NASS-GES.

II. Background

    In a June 1, 2000 notice (65 FR 34998), NHTSA announced its
intention to include consumer information ratings for rollover
resistance of passenger cars and light trucks in its New Car Assessment
Program (NCAP). NCAP has provided comparative consumer information on
vehicle performance in frontal and side impact crashes for many years.
About 22 percent of passenger car occupants killed in crashes are
killed in rollover crashes, as compared with more than 70 percent
killed in frontal and side crashes combined. In the case of light
trucks, however, about as many occupants are killed in rollover crashes
as in frontal and side crashes combined. NHTSA proposed a rating system
based on the Static Stability Factor (SSF) which is the ratio of one
half the track width to the center of gravity height.
    SSF was chosen over vehicle maneuver tests because it represents
the first order factors that determine vehicle rollover resistance in
the 95 percent of rollovers that are tripped. Driving maneuver tests
represent on-road untripped rollover crashes which are about 5 percent
of the total. Other reasons for selecting the SSF measure are: driving
maneuver test results are greatly influenced by SSF; the SSF is highly
correlated with actual crash statistics; it can be measured accurately
and explained to consumers; and changes in vehicle design to improve
SSF are unlikely to degrade other safety attributes.
    The industry comments to the June 2000 notice were that SSF was too
simple because it did not include the effects of suspension
deflections, tire traction and electronic stability control (ESC) and
that the influence of vehicle factors on rollover risk was so slight
that vehicles should not be rated for rollover resistance. In the
conference report dated October 23, 2000 of the FY2001 DOT
Appropriation Act, Congress permitted NHTSA to move forward with the
rollover rating proposal and directed the agency to fund a National
Academy of Sciences' study on vehicle rollover ratings. The study
topics are ``whether the static stability factor is a scientifically
valid measurement that presents practical, useful information to the
public including a comparison of the static stability factor test
versus a test with rollover metrics based on dynamic driving conditions
that may induce rollover events.''
    The Consumers Union (CU) commented to the June 2000 notice that
although SSF is a useful predictor of tripped rollover, it should be
used in

[[Page 35181]]

conjunction with a dynamic stability test using vehicle maneuvers to
better predict the risk of untripped rollovers. CU also believes that
NHTSA underestimated the incidence of on-road untripped rollover by
relying upon 1992-1996 data.
    Section 12 of the ``Transportation Recall, Enhancement,
Accountability and Documentation (TREAD) Act of November 2000''
reflects CU's concern. It directs the Secretary to ``develop a dynamic
test on rollovers by motor vehicles for a consumer information program;
and carry out a program conducting such tests. As the Secretary
develops a [rollover] test, the Secretary shall conduct a rulemaking to
determine how best to disseminate test results to the public.'' The
rulemaking and test program must be carried out by November 1, 2002.
This notice is part of NHTSA's work to satisfy the requirements of
Section 12 of the TREAD Act.
    NHTSA responded to these and other technical comments to the June
2000 notice in a January 12, 2001 notice (66 FR 3388) and announced the
agency's decision to use the SSF as a measure, along with publishing
the initial rollover resistance ratings. As of April 2001, the agency
has added the rollover resistance ratings of 104 vehicles to the
frontal and side crash ratings given by NCAP (see http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://www.nhtsa.dot.gov/hot/rollover/ for ratings, vehicle details and explanatory
information).
    NHTSA awarded a grant to the National Academy of Sciences for its
study of vehicle rollover ratings on December 15, 2000 and its first
public meeting on the subject took place on April 11 and 12, 2001. A
second open meeting will allow for consideration of alternatives to SSF
for rating vehicles, and presentations on consumer information and risk
communication. At a closed meeting the NAS committee will finalize its
draft report. The study will conclude with the required report to
Congress.

III. Preparatory Activity

    In response to the TREAD Act, NHTSA met with the Alliance of
Automobile Manufacturers, Nissan, Toyota, Ford, Consumers Union (CU),
Automotive Testing, Inc. (an independent test lab), MTS Systems Corp.,
the University of Michigan Transportation Research Institute (UMTRI),
Daimler-Chrysler, BMW, Volkswagen and Volvo to gather information on
possible approaches for dynamic rollover tests. These parties made
specific suggestions about approaches to dynamic testing of vehicle
rollover resistance. In addition, recent NHTSA research summarized in
the report entitled ``An Experimental Examination of Selected Maneuvers
That May Induce On-Road Untripped, Light Vehicle Rollover--Phase II of
NHTSA's 1997-1998 Vehicle Rollover Research Program'' \3\ is relevant
to the development of a dynamic rollover test suitable for inclusion in
our consumer information program.
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    \3\ Available at http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://www-nrd.nhtsa.dot.gov/vrtc/ca/rollover.htm.
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    This notice identifies a variety of dynamic rollover tests that we
have chosen to evaluate in our research program and what we believe to
be their potential advantages and disadvantages. It also discusses
other possible approaches we considered but decided not to pursue.
Table 1 summarizes the advantages and disadvantages we anticipate for
the various approaches prior to research which will increase our
understanding. We invite public comment on our decisions, on our
observations and on the general subject of rollover resistance testing
for consumer information.
    Track testing using the maneuvers discussed in this notice began in
April 2001 at NHTSA's Vehicle Research and Test Center in East Liberty,
Ohio. We intend to publish a second notice in early 2002 presenting a
tentative dynamic rollover test procedure chosen on the basis of this
research and the comments to today's notice. We will review the
comments to today's notice expeditiously and may revise the test
development research based on the comments. A final notice responding
to the comments to the second notice, presenting the final dynamic
rollover test procedure, and containing an initial set of rollover
resistance ratings will be published in October 2002.
    The test vehicles chosen for the evaluation of potential maneuver
tests are the 2001 Ford Escape (without electronic stability control
(ESC \4\)), the 2001 Chevrolet Blazer (without ESC), the 2001 Toyota
4Runner (with and without ESC enabled) and the 1999 Mercedes ML-320
(with and without ESC enabled). They represent the significant range of
static stability factors that characterize today's SUVs. They also
include two ESC systems with possible differences in operation. The
vehicles will be tested in a base load configuration with driver,
instruments and outriggers, in a second configuration with a roof load
to reduce SSF by .05, and in other load configurations intended to
influence handling. The loads will be positioned so as to change one
coordinate of the c.g. location without influencing the other two. For
example, in the second load configuration, about 200 pounds will be
secured to the roof in a position that maintains the fore-aft and side-
to-side location of the c.g. but raises it enough to cause a reduction
of 0.05 in the SSF (while also increasing the vehicle's mass moments of
inertia).
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    \4\ ESC is a safety system that can apply the brake at one or
more wheels automatically to keep the yaw rate of the vehicle
proportional to its speed and lateral acceleration. For example,
braking the outside front wheel can correct the heading of a vehicle
beginning to oversteer (spin out).
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    The test vehicles will be equipped with special wheel force sensors
at each wheel during some of the evaluation of potential maneuver
tests. They will provide better information for our evaluation of how
these vehicles react to different characteristics of the candidate test
maneuvers. Wheel force measurements will determine absolutely when two
wheel lift occurs. Also, they will allow us to measure the degree of
load transfer during runs that do not cause wheel lift, a capability
not possible in our previous research. The sensors also can reveal
possible interactions between vertical and lateral wheel forces that
maneuvers may produce in some vehicles.

IV. Difficulties Common to Various Dynamic Rollover Tests Using
Driving Maneuvers

    We considered some methods of dynamic testing for rollover
resistance that did not use driving maneuvers, but decided to
concentrate our research on driving maneuver tests for the reasons
discussed in Section VII. However, driving maneuver tests share some
significant difficulties in comparison to laboratory tests. Since they
directly represent a deadly type of crash, the safety of test drivers
will always be a concern, even though drivers will be belted and
outriggers will be used in most circumstances. Outriggers are the usual
means of minimizing the chance of an actual rollover crash during a
test, but they also introduce problems. If an outrigger digs into the
pavement, it can cause the vehicle to ``pole vault'' resulting in an
even worse rollover crash. The weight of the outrigger(s) may change
the vehicle's c.g. location and will increase its mass moments of
inertia, placing restraints on the natural desire to overdesign the
outriggers for safety. The mounting of the outrigger can also influence
vehicle handling by changing its structural stiffness. We will choose
outriggers designed to the best contemporary practices and evaluate
their effect on maneuver test results.
    Maneuver tests are expensive. Besides the labor involved in
performing the maneuvers and interpreting the results,

[[Page 35182]]

the test methods require that each test vehicle be custom fitted with
costly precision instruments, onboard computers, probably an array of
special steering and braking controls, and possibly telemetry. The
wheel force transducers included in these developmental tests are not
expected to be necessary for routine tests in a consumer information
program, but there may be a need for less intrusive means of load
transfer monitoring. Frequent tire changes, adding to cost and labor,
are necessary in maneuver tests because tire shoulder wear can
significantly influence force generation. Part of this research will
define the need for tire changes in the selected maneuver in routine
consumer information testing. Finally, damage to the vehicles as a
result of the tests or the installation of equipment is a cost factor.
    The use of driving maneuver tests to rate rollover resistance
presents some questions beyond test methodology, danger and expense. A
high statistical correlation based on a large sample of police reports
of rollover crashes was possible for the present ratings based on SSF
because SSF is a good predictor of tripped rollovers, in particular,
and the preponderance of rollovers in state crash reports are tripped.
As part of NHTSA' s dynamic maneuver test program in 1997 and 1998, we
tried to correlate the performance of the test vehicles on various
maneuvers to their rates of on-road untripped rollover crashes. We
found that it is not possible to obtain sufficient data, even on high
volume vehicles, to determine a correlation between maneuver test
outcome and untripped rollover involvement. The only data base we are
aware of that contains data identifying untripped rollover crashes is
NHTSA's NASS-CDS. However, only about 4300 crashes of all types
(frontal, side, rear and rollover) are researched in depth each year
for inclusion in this data base and only about ten of those cases are
untripped rollovers.\5\ The NASS-CDS data base is usually used with
weighting factors for different types of crashes to represent national
trends. However, the number of observations is too small to support
make/model correlations between maneuver test results and real-world
untripped rollover rates.
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    \5\ 1998-1999 NASS-CDS annual averages.
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    Some of the 17 states in NHTSA's State Data System (SDS) data base
\6\ attempt to distinguish between on-road and off-road rollover
crashes. While it seems inviting to use on-road rollover as a surrogate
for untripped rollover, this is not strictly accurate. Most on-road
rollovers occur when the vehicle is tripped by road surface
irregularities or the wheel rim digging into the pavement.\7\ Also,
police may code a rollover crash as ``on-road'' because the vehicle was
found at rest on the roadway. The designation ``on-road'' does not
necessarily mean that the roll initiation occurred on the roadway.
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    \6\ A collection of data from the police accident reports (PARs)
of 17 participating states. This data is limited to what was
recorded by the responding officer(s) at the time of the crash.
    \7\ ``Analysis of Untripped Rollovers''; Calspan Corporation for
American Automobile Manufacturer's Association and Association of
International Automobile Manufacturers; May 15, 1998, and ``NASS
Rollover Study Evaluation Report''; NHTSA National Center for
Statistics and Analysis; August 1998.
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    The correlation, by make/model, of performance in a maneuver test
to the rate of all rollovers would be highly dependent on the degree to
which good performance in the driving maneuver test is the result of
low c.g. height, large track width and other factors which also
increase resistance to tripped rollovers. Optimization of tire
properties and ESC operation for a particular maneuver test would
likely decrease this level of correlation over time if effective ways
of improving test performance are developed that do not improve the
tripped rollover resistance of vehicles. Therefore, it is unlikely that
the choice of any particular maneuver test or tests can be justified on
the basis of the correlation of the test results to real-world rollover
rates. This situation makes the resemblance of the chosen maneuver test
or tests to documented crash scenarios even more important.
    Ratings based on driving maneuvers may be complex and hard to
communicate to the public because the usual rollover criterion of two
wheel lift can be at odds with the handling capability of the vehicle.
In a path following maneuver, the test is terminated when the vehicle
can no longer follow the path. For example, consider a vehicle that
cannot negotiate the path beyond 38 mph, but it departs the path before
it achieves two wheel lift. Consider a second vehicle that can follow
the path at 45 mph but lifts the inside tires three inches off the
pavement. Which vehicle should be rated higher? Departing the roadway,
as the first vehicle would seem likely to do more often than the second
vehicle, can expose a vehicle to a high risk of tripped rollover.
    ESC was originally designed to keep the vehicle headed in the
direction desired by the driver rather than to plow-out (understeer) or
to spin-out (oversteer) in a limit cornering situation by using one or
more brakes to help turn the vehicle to the correct heading. ESC cannot
increase the maximum traction, and consequently prevent a vehicle from
leaving the road, if the vehicle is going too fast. ESC may help
drivers regain control rather than overreact in situations like an
abrupt ``road-edge recovery'' where there is sufficient traction to
recover. In this way, ESC has the potential to reduce the number of
single vehicle crashes that turn into tripped rollovers. However, ESC
can be programmed to work in many other ways. In one way, it can apply
the brakes automatically to slow the vehicle at a selected value of
lateral acceleration or at a similar criterion. While this is a
plausible safety strategy, it has the potential to overwhelm the other
aspects of vehicle behavior measured in a maneuver test. In most
maneuver tests, the vehicle is steered through the maneuver while
coasting because any attempt to keep a steady throttle position tends
to make the tests less repeatable. Even in a short maneuver, the
vehicle scrubs off some speed. For example, a vehicle entering a short
maneuver coasting at 50 mph is likely to exit at 45 mph or less.
However, with braking intervention programed into the ESC, a vehicle
could easily slow to 25 mph during the test. While both vehicles would
be rated on their entry speed, the ESC vehicle may be going much slower
at the critical part of the maneuver. It is possible that maneuver
tests could simply result in segregating vehicles with automatic brake
intervention from those without it. Automatic brake intervention may
produce some safety benefits. NHTSA believes, however, that the vast
majority of drivers also apply the brakes in difficult situations,
regardless of whether the vehicle has automatic brake intervention.
Thus, a maneuver test conducted while coasting could reward this type
of ESC design excessively. NHTSA expects that most drivers would brake
during similar maneuvers, and that automatic brake intervention would
make less difference in real driving than during tests in which drivers
are not permitted to brake.
    Important environmental conditions also will influence the results
of any driving maneuver test for rollover ratings. The pavement
friction of even a dedicated test area does not remain constant. There
is a cycle of polishing and weathering during periods of use and
disuse, and a possible temperature effect on pavement friction. The
usual method of determining pavement friction is a locked wheel braking
test conducted at a constant 40 mph using

[[Page 35183]]

a ``skid trailer'' with a water nozzle to wet the surface immediately
ahead of the skidding tire. The pavement friction coefficient generated
by this test is called the ``skid number''. General Motors has reported
that moderate differences in skid number, even when measured without
pavement wetting, do not correspond well to differences in lateral
force generated by vehicles on different pavements. Our planned test
program includes hot weather and cold weather testing as well as tests
conducted on different surfaces at three to date undetermined test
facilities. The result we hope for is a definition of a minimum
friction level for a valid test as tracked by tests using a control
vehicle.
    Not every vehicle is tested each year in the new car assessment
program. The results for vehicles without substantial changes tested in
previous years are carried over to represent vehicles of the current
model year. The test results, and the resulting rollover ratings, from
the previous year might not be comparable to the new year's results if
there were significant differences in pavement friction.

V. Path-Following Driving Maneuver Tests

    The driving maneuver tests for rollover resistance that have
received the most publicity over the years are the ``emergency double
lane change'' of Consumer Reports magazine and the European ``moose
test.'' The first test was the basis of criticism by Consumer Reports
that the 1988 Suzuki Samurai and the 1996 Isuzu Trooper were ``not
acceptable.'' The ``moose test'' was used by a European auto magazine
to demonstrate that the 1998 Mercedes-Benz A Class minicar could
experience on-road untripped rollover in a similar maneuver. We
classify both tests as path following tests to distinguish them from
another type of maneuver tests in which explicit steering inputs are
required without reference to the path they cause the vehicle to take.
We will evaluate both the CU double lane change (CU is the publisher of
Consumer Reports) and a version of the moose test recommended by
Daimler-Chrysler. We will also evaluate the use of mathematical path
correction and an automated steering controller \8\ to improve these
driving maneuver tests.
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    \8\ The automated steering controller was referred to as a
``Programmable Steering Machine'' in our June 1, 2000 notice (65 FR
34998).
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A. CU Double Lane Change

    The CU double lane change short course (figure 1) was developed in
order to replicate an unintentional rollover experienced by a Consumer
Reports staff member driving a Suzuki Samurai. It consists of a 70-
foot-long, 8-foot-wide entrance lane that is centered in a 12-foot-wide
first (right) lane, a 50-foot-long area to make the first lane change
(to the left), a set of gate cones at this 50-foot mark that are 12
feet apart (with the right cone three feet into the left lane), a 60-
foot-long area to make the second lane change back to the right lane,
and a 12-foot-wide exit lane. The test driver steers the vehicle
through the course at successively higher entry speeds until the
vehicle either plows out, spins out, or tips up. The vehicle is
coasting through the maneuver. The driver does not apply the brakes,
and driver releases the throttle 35 feet into the 70 foot entrance
lane.
    An advantage of the CU double lane change is its face validity,
that is, drivers can imagine a situation in which they may try to make
a similar maneuver. However, NHTSA believes that there are good
arguments that simply braking without steering or braking and steering
with an ABS equipped vehicle are better strategies to avoid the
hypothetical object in the road that is the basis of the CU test. In
addition, it is hard to find actual crashes that resemble the test.
Nevertheless, driving through a tight double lane change without wheel
lift is probably a good representation of what the public expects of a
personal vehicle.
    An important part of the double lane change is the immediate
steering reversal necessary to get back in the right lane after
steering sharply into the left lane to avoid the hypothetical object in
the roadway. This steering reversal allows the energy stored in the
suspension springs during the left steer and the roll momentum of the
sprung mass when that energy is released at the steering reversal to
add to the load transfer caused by the sharp right steer. The dynamics
of the steering reversal are not included in SSF, Tilt Table Ratio, or
even the J-turn maneuver (see 65 FR 34998 for details about these
rollover resistance metrics). So this aspect of the double lane change
better represents the dynamics that may result in an untripped
rollover.
    However, if the only criterion for success in a double lane change
maneuver is whether or not two-wheel lift can be made to occur, any
vehicle will pass such a test if equipped with tires of sufficiently
low traction or with chassis tuning that produces the same effect. In
this case, the vehicle will simply run off the desired path at a speed
and lateral acceleration too low to produce two-wheel lift. On the
other hand, an inherent advantage of path-following maneuvers like the
double lane change is that the maximum speed through the maneuver can
be used as part of the vehicle score to reward good handling and avoid
creating a rollover resistance rating with incentives for reduced
handling and braking performance. Like all the driving maneuvers we are
considering, the CU double lane change also has the advantage of
displaying the operation of electronic stability control systems.
    The foremost disadvantage of the CU double lane change is that
differences in driving style can strongly influence the test results.
The time history of the steering wheel angle may vary considerably for
runs of the same vehicle at the same speed (figure 2). Tests in which
the driver starts the steering movements earlier seem to produce a
moderately smaller initial left steer and a much smaller amount of
right steer after passing through the offset gate. The steering
reversal (from maximum left steer to maximum right steer) can vary
significantly at the same test speed, and the runs with a greater
steering reversal appear more likely to produce two-wheel lift. For
example, during CU tests of the Isuzu Trooper, one driver ran the
course at 37.5 mph with a left steer of 183 degrees followed by a right
steer of 216 degrees (399 degree steering reversal) and did not knock
down the course boundary cones or experience two-wheel lift. Another
driver ran the same course at 37.5 mph using an initial left steer of
191 degrees followed by a right steer of 388 degrees (579 degree
steering reversal) and experienced two-wheel lift.
    Another potential disadvantage of the double lane change maneuver
is the possibility that the course layout may cause the steering
reversal and roll momentum effect to be more critical for some vehicles
than for others. The course originally used by Consumer Reports had the
offset gate forcing the lane change positioned 60 feet from the end of
the entrance lane and also 60 feet from beginning of the exit lane.
When the publication tried to replicate its staff member's rollover
crash of a Suzuki Samurai, it found that shortening the distance from
the end of the entrance lane to the offset gate by 10 feet and moving
the offset gate three feet further to the left made two wheel lift of
the Samurai more likely. This suggests that tuning of the course to the
vehicle may be necessary to create a worst case condition and that a
course tuned to one vehicle may not be the worst case for another
vehicle to which it is compared.

[[Page 35184]]

B. VDA Double Lane Change

    The VDA Double Lane Change is a variant of the ``moose test'' used
by a Scandinavian automotive magazine. It was developed by the German
Alliance of Automotive Industry (VDA) to minimize the influence of
driving style on the original moose test for use as an industry
standard rollover and handling test procedure. As a double lane change
maneuver, it is identical in concept to the CU test, and it is useful
to contrast the two maneuvers.
    The method VDA used to minimize driver influence was to reduce the
lane and gate widths and tie these parameters to the width of the test
vehicle. Using the VDA course (figure 3) for a 70 inch wide vehicle
(typical of the most popular SUVs and mid-sized cars) the widths of the
entrance lane, offset gate, and exit lane are 7.25 feet, 9.12 feet and
9.9 feet, respectively, compared with 8 feet, 12 feet and 12 feet for
the same components of the CU double lane change course. The distance
from the end of the entrance lane to the beginning of the offset gate
is 44.3 feet rather than 50 feet for the CU test, and the distance from
the end of the offset gate to the beginning of the exit lane is only 41
feet, compared to 60 feet for the CU test. There is also a difference
in the amount of offset of the left lane gate. In the CU test, the
inside of the gate is offset 5 feet to the left of the inside of the
entrance lane and 3 feet to the left of the exit lane (because the exit
lane is 4 feet wider than the entrance lane). In the VDA test, the left
edges of the entrance and exit lanes are in line, and right edge of the
offset gate is 3.3 feet to the left.
    The fundamental difference between the CU and VDA courses is that
while the vehicle has to pass through a gate comprised of two cones
marking a 12 foot left lane width in the CU test, it has to traverse a
36-foot-long by 9.12-foot-wide left lane in the VDA test before turning
right to re-enter the right lane. The VDA test is more like a single
lane change to the left immediately followed by a second single lane
change to the right and does not have as sharp a steering reversal as
the CU double lane change test. In both tests, the vehicle begins to
coast about 35 feet before the end of the entrance lane.
    The VDA double lane change shares with the CU test the advantage of
face validity, but the VDA test would appear to be less subject to
variability in driving style. It also uses a rating criteria that
implicitly rewards good handling. It is scored by the maximum entry
speed of the vehicle's clean runs along with a notation of the limiting
event: understeer, oversteer or two-wheel lift. Like all the other
maneuver tests we are considering, it has the advantage of displaying
the operation of ESC systems, but the entry speed criteria may
disproportionately favor ESC systems with simple brake intervention.
    Efforts to reduce driver variability may also introduce problems.
The least serious problem is that narrow lanes may make the course so
hard to follow that imprecise driving rather than actual oversteer or
understeer may cause collisions with the course marking cones. Daimler-
Chrysler reports that expert drivers can negotiate the course at about
4 mph faster than average drivers. It is unclear whether this is due to
expert steering strategy optimizing the vehicle path for lower peak
lateral acceleration even within the reduced boundaries or simply to
better ability to judge cone position and control vehicle position. If
this problem exists, simply allowing the driver more tries at a given
speed may be all that is necessary to determine whether vehicle
handling is really the limiting factor.
    The more serious potential problem is the use of a 36 foot long
left lane, rather than just a gate to drive around. It potentially
removes the roll momentum effect associated with the sharp steering
reversals. While this effect increases the variability of CU test
results due to differences in driving style, it also reveals rollover
propensities that would not likely show up in a test like the J-turn.
    Assuming that the VDA double lane change does not suppress the
potential effects of unfavorable roll momentum, it also shares the
question of steering reversal timing with the CU test. Namely, does the
course layout present a worst case timing in which roll momentum
reinforces the side to side load transfer at peak lateral acceleration
for some vehicles but not for others?

C. Open-Loop Pseudo-Double Lane Change

    In its 1997-1998 rollover research, NHTSA made use of an automated
steering controller to achieve highly repeatable J-turn and fish hook
maneuvers. As discussed above, the potential problems of double lane
change tests are the lack of repeatability caused by variations in
driving style and the possibility that a course producing worst case
roll momentum for one vehicle may not do so for the next vehicle. We
will attempt to solve these problems by using the steering controller
in a non-path following maneuver approximating a double lane change.
    The idea is to use steering rates and magnitudes typical of driver-
controlled CU tests, but to use the automated controller for
repeatability. Separate circular path tests of each vehicle would be
done to relate lateral acceleration to steering angle in the linear
range. This information would be used to tailor the steering angles for
the pseudo-double lane change to the steering ratio and wheelbase of
each test vehicle. The steering controller would also tailor the course
for the worst case roll momentum for each vehicle. Body roll rate
feedback would be used to time the first steering reversal left to
right and also the second steering reversal right to straight ahead.
    This is not a maneuver established in literature or in practice. It
is little more than a concept now. Its potential drawback is that the
maneuver may stray too far from an actual double lane change to retain
any face validity. Also, it is unclear if the advantage of a simple
speed and limit circumstance score would remain applicable to a double
lane change performed in this manner.

D. Path-Corrected Limit Lane Change

    From a vehicle manufacturer's prospective, the double lane change
maneuver is a good test to evaluate a vehicle's limit handling
behavior, because it is a realistic maneuver and it allows engineers to
simultaneously evaluate the three main behaviors that affect limit
handling safety (responsiveness, lateral stability and rollover
resistance). However, lane changes are driver-dependent (meaning
vehicle performance is heavily influenced by how the driver drives the
vehicle) and their rating scales are usually subjective (meaning based
on driver expert evaluation rather than on measured data). To solve
this problem, Ford Motor Company has developed Path-Corrected Limit
Lane Change (PCLLC). It is claimed to be a driver-independent,
objective way to run limit handling lane changes. First, vehicles are
run through a series of maneuvers much like the CU double lane change
except that a range of course lengths and degrees of lane offsets are
used to measure their responses to steering inputs in a range of
frequencies. The data is then normalized mathematically to show how
each of those vehicles would have performed had they followed precisely
the same paths in the lane change. This is what ``Path-Correction''
means, and this normalization reduces the driver influence in the
maneuver.
    PCLLC is a proprietary technique, and the details have not been
reported publicly by Ford. Ford is allowing

[[Page 35185]]

NHTSA to evaluate this technique under a confidentiality agreement.
NHTSA will run Ford's specified suite of vehicle characterization tests
using its own vehicles and test track with Ford's assistance in
instrumenting the vehicles for the measurements required for the
mathematical path corrections. Ford will explain the theory of the
mathematical corrections to NHTSA, and perform the corrections on
NHTSA's vehicle test data in a confidential report. If NHTSA decides to
propose this technique as the best way of accomplishing the dynamic
rollover tests required by the TREAD Act, it expects that Ford will
release it from the confidentiality agreement so that the test
procedure can be proposed in detail in our next notice early in 2002.
    We view PCLLC as a mathematical technique which allows the
construction of ``perfect test runs'' for an objective comparison of
vehicles from a suite of similar test runs which expose each vehicle to
a range of speeds, steering frequencies, rates and amplitudes. It looks
like a good approach to overcoming the disadvantages discussed earlier
for the more conventional driver controlled lane change maneuver tests.
Driving style variability would clearly be eliminated, and it appears
that this technique can construct a number of standard paths to examine
the question of how many courses are necessary for a fair evaluation of
the roll momentum effect for vehicles with different properties.
    NHTSA has envisioned that PCLLC could be used as a way of producing
the equivalent of a CU double lane change test with every vehicle
following exactly the same geometric path up to the point that it
either has two-wheel lift or can no longer maintain the prescribed path
as a result of limit understeer or oversteer. Under this idea, the
rating criteria could be speed and the limiting circumstance (plow,
spin or two wheel lift) as with the Daimler-Chrysler recommendation,
with the possibility of greater rating complexity if more than one test
course were required.
    However, it is not clear whether the PCLLC technique can be used
this way and whether this would be the best way to use it. Ford is
looking at many different vehicle handling metrics and cited three
examples. Responsiveness could be represented by a delay time from
steering input to yaw response evaluated on a path corrected to the
same time history of yaw angle for each vehicle. Lateral stability
could be characterized by rear tire slip angle on a path corrected to
equal lateral acceleration for each vehicle. Untripped rollover
resistance could be characterized by the degree of side to side load
transfer evaluated on a path representing the maximum lateral
acceleration capacity of the vehicle (considering such factors as
practical limits on steering angle and rate and limit oversteer). Since
the vehicle characterization runs are performed with ESC operating, the
results should reflect its influence in the same way as other driving
maneuver tests.

VI. Open Loop Fishhook Maneuvers--Defined Steering Tests

    The fishhook maneuver was originally developed by Toyota Motor
Corporation as a maneuver with a strong roll momentum effect and a
simple steering regime that would be fairly repeatable by test drivers.
The maneuver requires the driver to steer as quickly as possible 270
degrees of steering wheel angle, and then to steer 870 degrees in the
opposite direction as quickly as possible (figure 4). At less than
limit speed runs, the vehicle's path resembles a fishhook shape (figure
5), but the actual path is immaterial to the scoring. The maneuver is
repeated in each direction of initial steering and at increasing speed
until two-wheel lift or loss of control occurs, or until preset maximum
speed for test driver safety is reached. Toyota also added pulse
braking \9\ to make the maneuver more likely to induce two-wheel lift
if the vehicle under test would not lift wheels without braking. The
lateral acceleration at two-wheel lift (LAR) is Toyota's figure of
merit for this maneuver.
---------------------------------------------------------------------------

    \9\ Pulse braking is a short hard brake application that creates
a transient increase in lateral acceleration upon release.
---------------------------------------------------------------------------

    NHTSA's 1997-98 research program made use of two variations on the
Toyota ``fishhook'' maneuver theme. Since these tests are described by
the steering input without regard for different paths taken by
different vehicles, they are considered ``open-loop''. They were also
perfect candidates for NHTSA's goal of using an automated steering
controller for precise repeatability for maximum objectivity. NHTSA's
tests did not use pulse braking because we were concerned that pulse
braking tests were not merely a more stringent level of the basic
fishhook, but a test of different vehicle dynamics. In one version, the
steering rate was set at 750 degrees per second for all vehicles and
the dwell time \10\ between steering reversals was ``tuned'' for each
vehicle to resemble half a sine wave at what we thought was the roll
natural frequency of each vehicle. In the other variation, we attempted
to represent a road edge recovery maneuver by setting the initial steer
angle to 7.5 degrees of the road wheels (to represent the front tire
slip angle possible when a vehicle mounts a four inch pavement height
above the road shoulder), using a constant 0.5 second dwell time and a
more moderate steering rate of 500 steering wheel degrees per second.
The first maneuver was generally more severe than the second. It was
configured to represent a steering frequency of 0.5 Hz, which was the
roll natural frequency assumed for most vehicles because our attempts
at measuring roll natural frequency were thwarted by vehicle suspension
damping. However, some of the vehicles responded with greater load
transfer to the seemingly gentler ``road-edge recovery'' fishhook which
used a different steering frequency. This suggests the possible
importance of roll momentum timing.
---------------------------------------------------------------------------

    \10\ Dwell time is the short time internval of less than one
second between the initial steering angle (shown as negative angle
in Figure 4) and larger steering movement in the reverse direction.
---------------------------------------------------------------------------

    Open loop fishhook maneuver tests are like the mirror image of the
double lane change tests because their principle advantages and
disadvantages are reversed. Aided by a steering controller, driving
style differences are absolutely eliminated. These maneuvers also
present the best possibility for tuning the maneuver to the roll
characteristics of each test vehicle, thereby eliminating the suspicion
that the steering frequency of a fixed double lane change makes the
test inherently more stringent for some vehicles than others. However,
the fishhook maneuver has much less face validity than the double lane
change maneuver. Even the ``road edge recovery'' version of the
fishhook does not look, to a ordinary driver, like a maneuver he or she
would ever be called upon to make.
    There is another disadvantage to open loop tests. Because the
vehicle path does not matter, two-wheel lift can be prevented simply by
using tires of sufficiently low traction or chassis tuning that
produces the same effect. Unless an open loop test is accompanied by
other tests of specific handling properties, it could have the perverse
effect of encouraging manufacturers to sacrifice handling and braking
to make superficial refinements to improve a rollover rating. Also,
improvements in a rollover rating gained by special original equipment
tire properties may be negated when the tires are replaced later in the
life of the vehicle.
    NHTSA will evaluate three types of fishhook maneuvers. In one
maneuver the counter steer will be limited to about 500 to 600 degrees,
rather than

[[Page 35186]]

870, because the large countersteer is thought to scrub off so much
speed that it reduces the severity of the maneuver. Also, instead of a
fixed 270 degree initial steer, a steering wheel angle derived from the
steering angle causing a fixed lateral acceleration, in the linear
range, will be chosen to put vehicles with differences in steering gear
ratio and wheelbase on an equal footing. A fixed steering rate of 720
degrees per second and a fixed time from the beginning of steering to
its return to zero angle during countersteer will be used.
    In the second fishhook, the timing of the steering reversal will be
based on roll rate feedback. The worse case roll momentum effect is
expected when the start of the steering reversal coincides with the
instant of maximum roll angle resulting from the first steer. We expect
to use an approximate zero reading of a roll rate sensor to indicate
maximum roll angle and trigger the countersteer by the automatic
steering controller.
    The third variation will use a counter steer timing technique
suggested by Nissan (figure 6). In this method, the first part of the
fishhook is studied separately prior to the fishhook test maneuvers in
order to define the worst case dwell time. This is done by running a
step steer maneuver (the same as a J turn) at the same steering rate
and maximum angle as the first steering movement of the fishhook. The
roll rate is measured to determine the time of the maximum roll angle
of the second oscillation. Nissan believes that the most severe
fishhook for each vehicle is the one in which the lateral acceleration
zero crossing during countersteering in the fishhook occurs at the
second oscillation peak time as measured in the J turn maneuver. The
dwell time from initial steer to countersteer would be adjusted
accordingly. The theoretical basis for Nissan's observation on fishhook
severity is not obvious. Nissan's belief is based on experimental
studies during which dwell time was varied. Its technique appears to
produce a countersteer timing similar to that produced by roll rate
feedback.
    As mentioned above, fishhook tests contain no inherent
disincentives for rollover resistance strategies that sacrifice
handling. NHTSA is considering adding some objective measure of
handling ability to any fishhook test used for consumer information. We
are considering a steering response time test possibly based on a J-
turn (step steer) and a maximum lateral acceleration test based on
either a constant steer input with slowly increasing speed regime or a
constant speed with slowly increasing steer regime. We are concerned,
however, that even this limited NHTSA definition of handling may
produce undesirable trade-offs of less measurable aspects of vehicle
handling when manufacturers design to the test. We are particularly
interested in comments on how likely it is that vehicle manufacturers
would make such trade-offs to ``beat'' the test.

VII. Dynamic Tests Other Than Driving Maneuvers

    NHTSA also considered two dynamic tests that did not involve
driving maneuvers, namely the centrifuge test and driving maneuver
simulation using computational models. Both of these tests have the
major benefit of being independent of pavement friction, whereas the
problem of pavement friction variation is perhaps the most vexing issue
common to all the driving maneuver tests discussed above. However, we
decided not to include these tests in our research plan under TREAD for
the reasons explained below.

A. Centrifuge Test

    The test device for the centrifuge test is similar in concept to a
merry-go-round. A person seated at the edge of the merry-go-round feels
a lateral force pushing him or her away from the spinning surface that
increases with the rotational speed of the merry-go-round. The
centrifuge device test (figure 7) consists of an arm attached to a
powered vertical shaft. At the end of the arm is a horizontal platform
upon which the test vehicle is parked. As the vertical shaft rotates,
the parked vehicle is subjected to a lateral acceleration that can be
precisely controlled and measured. The basic measurement is the lateral
acceleration at which the parked vehicle experiences two-wheel lift.
The outside tires are restrained by a low curb so the measurement is
independent of surface friction, and the vehicle is tethered to prevent
excessive wheel lift. This test method was suggested by the University
of Michigan Transportation Research Institute (UMTRI) both in comments
to our notice about the present rollover resistance ratings and more
recently in the context of the TREAD Act. The test method is directed
primarily at tripped rollover, which UMTRI noted accounts for all but a
small percentage of rollovers.
    The centrifuge test has many advantages. It can produce
measurements which are accurate, repeatable and economical in labor
costs. It includes the effects of tire and suspension deflections, and
its measurements would be expected to correlate well with the actual
rollover rates of vehicles, because those statistics are largely driven
by tripped rollovers. The centrifuge test is arguably more accurate
than SSF in evaluating tripped rollover resistance because it evaluates
the outward c.g. movement as a result of suspension and tire
deflections. Its basic measurement of a vehicle, lateral acceleration
at two-wheel lift, is roughly 15 percent less than the vehicle's SSF
with about a +/-5 percent range to cover extremes in roll stiffness.
    Despite these advantages, we did not choose to investigate the
centrifuge test under the TREAD Act. Improvements in centrifuge test
performance can be made by suspension changes that degrade handling.
The best performance in the centrifuge test (and in the closely related
but less accurate tilt table test) occurs when the front and rear
inside tires lift from the platform at the same time. The tuning of the
relative front/rear suspension roll stiffness to accomplish this will
cause the vehicle to oversteer more than most manufacturers would
otherwise desire. We do not want to tempt manufacturers to make this
kind of trade-off. Further, we understood the intention behind TREAD to
be that NHTSA should give the American public information on
performance in a driving maneuver that would evaluate the performance
of new technologies like ESC. The centrifuge test would not do so.

B. Driving Maneuver Simulation

    Computational models that simulate test maneuvers are used by
vehicle manufacturers to assess handling and rollover performance of
vehicle designs prior to building prototypes, and to evaluate the
effect of suspension changes in prototypes and production vehicles.
They present a potential solution to the safety, repeatability and
pavement surface variability of real driving maneuver tests.
Unfortunately, simulations now also carry enough disadvantages to
disqualify their use for rollover resistance ratings. The various
models used by different manufacturers produce different results,
especially in simulating limit maneuvers. There is no agreement among
manufacturers on a single model sufficient for this purpose. The time
and cost of measuring the vehicle properties necessary for a limit
maneuver model exceed that of running a real driving maneuver test.
Validation testing of a model is necessary and greatly resembles the
real tests the model hoped to avoid. Testing of the operation of ESC is
problematic because the algorithms are often proprietary at the
supplier level and not well known by the vehicle manufacturers. Given
these difficulties, NHTSA has concluded that it is extremely unlikely

[[Page 35187]]

they could be resolved in time for us to use computer modeling for the
information we must provide to the American public beginning in
November 2002.

VIII. Solicitation of Comments

    NHTSA solicits general and specific comments on the subject of the
development of a dynamic test for vehicle rollover resistance. We also
wish to bring the following specific questions to the attention of
commenters:
    1. NHTSA has decided to devote its available time and resources
under the TREAD Act to develop a dynamic test for rollover based on
driving maneuver tests. Is this the best approach to satisfy the intent
of Congress in the time allotted? Are there additional maneuvers that
NHTSA should be evaluating? Which maneuver or combination of maneuvers
do you believe is the best for rollover rating? Are these other
approaches well enough developed and validated that they could be
implemented 18 months from now?
    2. How should NHTSA address the problem of long term and short term
variations in pavement friction in conducting comparative driving
maneuver tests of vehicle rollover resistance for a continuing program
of consumer information?
    3. Some ESC systems presently have two functions. One is yaw
stability which uses one or more brakes to keep the vehicle headed in
the right direction in a limit maneuver, and the other is simple brake
intervention in excess of the braking required for yaw stability. It is
expected that the presence of a brake intervention function in ESC will
have a large effect on the rating of vehicles because the average speed
through a given test maneuver for vehicles having this function will be
much less than for vehicles without it (even if equipped with ESC for
yaw stability) under the usual test protocols of coasting through
maneuvers and using the entry speed as the test speed. Is the value
given to the brake intervention function of ESC as opposed to the yaw
stability function by potential rollover rating tests commensurate with
its safety value to consumers? Please provide all the data and
reasoning that support your view. Should NHTSA measure the vehicle
speed at the completion of the maneuver as well as vehicle speed at
entry?
    4. If open-loop (defined steering input) maneuvers are used to
determine whether a vehicle is susceptible to two wheel lift as a
result of severe steering actions, superficial changes that reduce tire
traction or otherwise reduce vehicle handling (but prevent wheel lift)
would be rewarded the same as more fundamental or costly improvements.
The same is true of closed loop (path following) maneuvers that use
wheel lift as the sole criterion. Should measures of vehicle handling
be reported so that consumers can be aware of possible trade-offs. What
indicators of vehicles handling would be appropriate to measure and how
should this consumer information be reported?
    5. What criteria should NHTSA use to select the best vehicle
maneuver test for rollover resistance? Should the maneuver that has the
greatest chance of producing two wheel lift in susceptible vehicles be
chosen regardless of its resemblance to driving situations? Is it more
important that the maneuver resemble an emergency maneuver that
consumers can visualize? How important is objectivity and
repeatability?

IX. Rulemaking Analyses and Notices

Executive Order 12866

    This request for comment was not reviewed under Executive Order
12866 (Regulatory Planning and Review). Agency actions to develop tests
for NHTSA's New Car Assessment Program are not rulemaking actions
because the program does not impose requirements on any party.

X. Submission of Comments

A. How Can I Influence NHTSA's Thinking on This Document?

    In developing this document, we tried to address the concerns of
all our stakeholders. Your comments will help us improve this notice.
We invite you to provide different views on options we propose, new
approaches we have not considered, new data, how this document may
affect you, or other relevant information. We welcome your views on all
aspects of this document, but request comments on specific issues
throughout this document. Your comments will be most effective if you
follow the suggestions below:
     Explain your views and reasoning as clearly as possible.
     Provide solid technical and cost data to support your
views.
     If you estimate potential costs, explain how you arrived
at the estimate.
     Tell us which parts of this document you support, as well
as those with which you disagree.
     Provide specific examples to illustrate your concerns.
     Offer specific alternatives.
     Refer your comments to specific sections of this document.
     Be sure to include the name, date, and docket number with
your comments.

B. How Do I Prepare and Submit Comments?

    Your comments must be written and in English. To ensure that your
comments are correctly filed in the Docket, please include the docket
number of this document in your comments.
    Your comments must not be more than 15 pages long. (49 CFR 553.21).
We established this limit to encourage you to write your primary
comments in a concise fashion. However, you may attach necessary
additional documents to your comments. There is no limit on the length
of the attachments.
    Please submit two copies of your comments, including the
attachments, to Docket Management at the address given above under
ADDRESSES.
    Comments may also be submitted to the docket electronically by
logging onto the Dockets Management System website at http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://dms.dot.gov. Click on ``Help & Information'' or ``Help/Info'' to obtain
instructions for filing the document electronically.

C. How Can I Be Sure That My Comments Were Received?

    If you wish Docket Management to notify you upon its receipt of
your comments, enclose a self-addressed, stamped postcard in the
envelope containing your comments. Upon receiving your comments, Docket
Management will return the postcard by mail.

D. How Do I Submit Confidential Business Information?

    If you wish to submit any information under a claim of
confidentiality, you should submit three copies of your complete
submission, including the information you claim to be confidential
business information, to the Chief Counsel, NHTSA, at the address given
above under FOR FURTHER INFORMATION CONTACT. In addition, you should
submit two copies, from which you have deleted the claimed confidential
business information, to Docket Management. When you send a comment
containing information claimed to be confidential business information,
you should include a cover letter setting forth the information
specified in our confidential business information regulation. (49 CFR
Part 512.)

[[Page 35188]]

E. Will the Agency Consider Late Comments?

    We will consider all comments that Docket Management receives
before the close of business on the comment closing date indicated
above under DATES. To the extent possible, we will also consider
comments that Docket Management receives after that date. However, late
comments will not likely be able to influence our testing program. We
encourage commenters to respond as soon as possible since the testing
described in this notice is already underway. If Docket Management
receives a comment too late for us to consider it in completing our
test program developing a proposal on dynamic rollover performance, we
will consider that comment as an informal suggestion for future
enhancements to our rollover program.

F. How Can I Read the Comments Submitted by Other People?

    You may read the comments received by Docket Management at the
address given above under ADDRESSES. The hours of the Docket are
indicated above in the same location.
    You may also see the comments on the Internet. To read the comments
on the Internet, take the following steps:
    (1) Go to the Docket Management System (DMS) Web page of the
Department of Transportation (http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://dms.dot.gov/).
    (2) On that page, click on ``search.''
    (3) On the next page (http://frwebgate.access.gpo.gov/cgi-bin/leaving.cgi?from=leavingFR.html&log=linklog&to=http://dms.dot.gov/search/), type in the
four-digit docket number shown at the beginning of this document.
Example: If the docket number were ``NHTSA-1998-1234,'' you would type
``1234.'' After typing the docket number, click on ``search.''
    (4) On the next page, which contains docket summary information for
the docket you selected, click on the desired comments. You may
download the comments. Although the comments are imaged documents,
instead of word processing documents, the ``pdf'' versions of the
documents are word searchable.
    Please note that even after the comment closing date, we will
continue to file relevant information in the Docket as it becomes
available. Further, some people may submit late comments. Accordingly,
we recommend that you periodically check the Docket for new material.

G. Plain Language

    Executive Order 12866 requires each agency to write all rules in
plain language. Application of the principles of plain language
includes consideration of the following questions:
     Have we organized the material to suit the public's needs?
     Are the requirements in the rule clearly stated?
     Does the rule contain technical language or jargon that is
not clear?
     Would a different format (grouping and order of sections,
use of headings, paragraphing) make the rule easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by adding tables, lists, or
diagrams?
     What else could we do to make the rule easier to
understand?
    If you have any responses to these questions, please include them
in your comments on this document.

    Issued on June 27, 2001.
Stephen R. Kratzke,
Associate Administrator for Safety Performance Standards.

Table 1.--Summary of Anticipated Advantages and Disadvantages for
Possible Dynamic Rollover Tests

    Note: The extent to which many of these anticipated attributes
are realized will not be known until the completion of the resesarch
project.

1. Path Following Driving Maneuver Tests

A. CU Double Lane Change
    Anticipated advantages: Familiar to the public, represents a real
maneuver, considers roll momentum, use of speed as criteria implicitly
rewards good handling, demonstrates action of ESC.
    Anticipated disadvantages: Poor repeatability due to large driver
influence, use of wheel lift as main criterion invites trade-offs in
tire traction, may operate at a worst case suspension frequency for
some vehicles but not others.
B. VDA/ISO/Moose Test
    Anticipated advantages: Like CU but with less room for driver
variability through tight cone placement, represents a real maneuver,
use of speed as criteria implicitly rewards good handling, demonstrates
action of ESC.
    Anticipated disadvantages: Driver influence is reported to be still
on the order of 4 mph, tight lane widths may test driver ability as
much a vehicle handling, more like 2 back to back single lane changes--
may not include roll momentum, may operate at a worst case suspension
frequency for some vehicles but not others (course adjustments for
wheelbase mentioned).
C. Open Loop Pseudo-Double Lane Change (Concept for Automating the CU
to the Extent Possible Using a Automated Steering Controller)
    Anticipated advantages: Eliminates repeatability issues due to
driver influences, attempts to represent a real maneuver, considers
roll momentum, may use roll feedback to find worst case steering timing
for each vehicle, use of speed as criteria implicitly rewards good
handling? demonstrates action of ESC.
    Anticipated disadvantages: Exists only as a concept--may prove to
be entirely impractical, use of wheel lift as main criterion invites
trade-offs in tire traction, failure to replicate a realistic path
would devalue face validity and speed criterion, may be difficult to
develop with available resources.
D. Ford Path Corrected Limit Lane Change
    Anticipated advantages: Objective and repeatable, can it
``perfect'' the double lane change? considers roll momentum,
demonstrates action of ESC.
    Anticipated disadvantages: Suggested criteria requires handling
definition and still may reward poor tire traction as it currently
operates, rollover resistance is rated on different paths for different
vehicles.

2. Open Loop ( Defined Steering) Fishhook Maneuver Tests (With Several
Steering Timing Ideas To Be Evaluated)

    Anticipated advantages: Performed by automated steering controller
for maximum objectivity and repeatability, considers roll momentum and
seeks worst case for every vehicle, demonstrates action of ESC.
    Anticipated disadvantages: Lacks face validity of lane change
maneuvers, actual paths may differ widely between vehicles, needs
separate handling criteria because poor tire traction is otherwise
rewarded.

3. Dynamic Tests Other Than Driving Maneuvers--Not Planned for
Evaluation

A. Centrifuge
    Advantages: A ``perfection'' of the well known tilt table,
expandable to test performance at road perturbations, accounts for
suspension and tire deflections (unlike SSF), can represent tripped
rollover (like SSF), accurate, repeatable and relatively cheap
measurements.
    Disadvantages: Suspension optimization for centrifuge test score
can degrade handling (unlike SSF), not be perceived as ``dynamic
enough'' for TREAD requirements, does not demonstrate action of ESC.

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B. Mathematic Simulation
    Advantages: Objective and repeatable, solves pavement friction
issues, any maneuver is possible.
    Disadvantages: Cost of vehicle characterization even greater than
for maneuver tests, ESC algorithms proprietary and possibly not known
to vehicle mfgr., no universally accepted mathematic model.

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[FR Doc. 01-16659 Filed 7-2-01; 8:45 am]
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