Flat tires and Blowouts

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    There are many factors that influence crashes of these types. For blowouts, there is speed, tire pressure, and the load on the vehicle. Blowouts to the front tire can cause roadway departure, or can cause a lane change resulting in a head-on crash. Blowouts in a rear tire can cause spinning out and loss of control. As discussed in the target population section, a target population can be estimated for tire problems, but the agency doesn’t know how many of these crashes are influenced by under-inflation. However, reducing under-inflation will be a real benefit in reducing flat tires and blowouts. The agency’s best estimates of these effects are discussed below.

    The target population is 414 fatalities and 10,275 non-fatal injuries that occur annually in light vehicles in which the cause of the crash is a flat tire/blowout. It is difficult to determine the impacts of under-inflation. Puncture is the most common reason for a blowout. However, there are also many cases where a tire is punctured, loses air, and then fails later after being driven a distance under-inflated. In these cases, a TPMS would provide information of the low tire pressure before the tire failed. We are assuming that under-inflation is involved in 20 percent of the cases that caused the crash. At the same time, we realize that the influence that under-inflation has on the chances of a blowout are influenced by the properties of the tire. Thus, we believe that better tires could take care of 50 percent of this problem and are assigning this value to the tire upgrade rulemaking. In conclusion, it is estimated that 41 fatalities (414 x .2 x .5) and 1,028 injuries are caused annually by flat tires/blowouts, where under-inflation is the cause of the flat tire/blowout. At the same time we estimate that there are 41 fatalities and 1,028 injuries in the target population for better tires brought about by the tire upgrade rulemaking.

    The agency assumes that 90 percent of drivers will fill their tires back to placard pressure when given a warning. For this situation, the agency does not believe that the steady state analysis has any impacts on the benefits. Any tire above the warning level is not very susceptible to a flat tire, and it probably doesn’t matter whether the tire is at a placard level of 30 psi or at a steady state level of say 27 psi in terms of its likelihood of failing due to a flat tire. We also apply a .99 factor to take into account the one percent of the fleet that already has a direct measurement system.

    Thus, the benefits for flat tires/blowouts for Compliance Options 1 through 3 are the same: 37 lives saved (41 x .90 x .99) and 916 injuries reduced (1,028 x .90 x .99) Non-fatal injuries are divided into the AIS levels based on the injury levels in 1995-98 NASS-CDS distribution of injuries in vehicles with flat tires causing the crash. These are:  AIS 1 = 80.1 percent, AIS 2 = 14.4 percent, AIS 3 = 3.5 percent, AIS 4 = 1.5 percent, AIS 5 = 0.5 percent.

    Total Quantifiable Safety Benefits

    Table V-24 provides the total quantifiable safety benefits by Compliance Option adding together the benefits for skidding/loss of control, stopping distance, and flat tires/blowouts.


Table V-24
Quantifiable Safety Benefit Impacts
  MAIS 1 MAIS 2 MAIS 3 MAIS 4 MAIS 5 Non-Fatal Total Fatal
Opt 1              
Skid -3,529 -393 -168 -16 -10 -4,116 -44
Stop -2,900 -442 -166 -17 -11 -3,536 -40
Flat -733 -132 -32 -14 -5 -916 -37
Total -7,162 -967 -366 -47 -26 -8,568 -121
               
Opt 2              
Skid -3,529 -393 -168 -16 -10 -4,116 -44
Stop -2,739 -418 -157 -17 -10 -3,341 -38
Flat -733 -132 -32 -14 -5 -916 -37
Total -7,001 -943 -357 -47 -25 -8,373 -119
               
Opt 3              
Skid -3,529 -393 -168 -16 -10 -4,116 -44
Stop -2,739 -418 -157 -17 -10 -3,341 -38
Flat -733 -132 -32 -14 -5 -916 -37
Total -7,001 -943 -357 -47 -25 -8,373 -119

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