Interpretation ID: 18475-2.drn

Dear <Confidential>

This responds to your letter requesting an interpretation of how S5.1 of Standard No. 214, Side impact protection applies to your company's planned passenger car with a new side door system feature. As explained below, the Thoracic Trauma Index (TTI(d)) for the car must not exceed the 90 g requirement applicable to passenger cars with two side doors.

Your new side door system feature can generally be described as follows:

The side door system is that of a conventional 2-door vehicle with certain variations. The front portion of the side door system is identical in structure to that of the side door on a conventional 2-door vehicle. Access to the rear seat is possible using the front portion of the side door system alone. The side door system also includes a narrow rear access door panel. This panel cannot be opened independently of the front portion of the side door system. There is no structure between the front portion of the side door system and the rear access door panel.

I note that this type of side door system could be used on one or both sides of a vehicle. For ease of discussion, we will address the situation where it would be used on both sides. However, our interpretation would not differ if the system is used on one side of a vehicle.

Standard No. 214's dynamic performance requirements are set forth in paragraph S5. The performance requirements for passenger cars differ for 2-door cars and 4-door cars. More specifically, under S5.1, the Thoracic Trauma Index (TTI(d)) may not exceed 85 g for passenger cars with four side doors, and 90 g for passenger cars with two side doors.

The issue raised by your letter is whether passenger cars equipped with your new side door system would be considered 2-door cars or 4-door cars for purposes of S5.1. Put another way, the issue is whether the front portion of the side door system and the rear access panel would be counted as separate doors in determining whether the vehicle is a 2-door car or 4-door car.

We note that this issue is not directly addressed by the language of Standard No. 214. Among other things, the standard does not include a definition of "door." It is therefore especially appropriate, in interpreting the standard, to look to the purposes behind the different performance requirements for 2-door cars and 4-door cars.

In the preamble to the final rule establishing the different performance requirements for 2-door cars and 4-doors (see 55 FR 45722; October 30, 1990), the agency provided the following explanation:

Another important issue, however, is technological feasibility. In particular, based on its review of the record, NHTSA is concerned about the ability of manufacturers to achieve TTI(d) lower than 90 g for all of their two-door cars, and lower than 85 g for all of their four-door cars.

NHTSA believes that it is generally more difficult for manufacturers to achieve lower TTI(d) for two-door cars than for four-door cars. The reason for this is that the side structure and geometry of two-door cars is different from four-door cars. For example, since the door on a two-door model is typically wider than on a four-door model, it is more difficult to design as strong a structure for the door on the two-door model. Taking into account the confidential data submitted by the manufacturers and other available data, the agency has six sets of data on two-door and four-door versions of the same model. These data indicate that the driver dummy injury measurements in a two-door car are about 14 percent higher than in a four-door car. NHTSA also observes that of 22 two-door cars for which the agency has data, only one had driver TTI(d) less than 80, only two had less than 85 g, and only five had less than 90 g.

(55 FR 45746-45757.)

The primary rationale for the slightly higher TTI(d) limit for 2-door cars was thus the difference in side structure and geometry of 2-door cars and 4-door cars, including but not limited to the wider doors typically used for 2-door cars.

The side structure and geometry of the car design at issue is comparable to that of a typical 2-door car rather than a 4-door car. As discussed above, the front portion of the side door system is identical in structure to that of a conventional 2-door vehicle, and access to the rear seat, using the front portion of the side door system alone, is possible. The front portion of the side door system, by itself, thus has the width of the wider doors typically used for 2-door cars. Moreover, there is no structural component between the front portion of the side door system and the rear access door panel.

Given that it is unclear from the language of Standard No. 214 whether the rear access door panel should (considering its small size) cause the vehicles in question to be regarded as 4-door cars, and given the new side door system has the same characteristics that led the agency to establish a slightly higher TTI(d) limit for 2-door cars, the agency concludes that the vehicles should be considered 2-door cars for purposes of determining S5.1's applicable TTI(d) limits.

I note that because this interpretation is based in large part on the policy determinations behind establishing different TTI(d) limits for 2-door and 4-door cars, it should not be viewed as precedent for how we would interpret the term "door" in other contexts.

NHTSA grants your letter's request for confidential treatment of certain information and will keep the identity of your company confidential. The information in publicly available copies of the letter will be redacted.

I hope this information is helpful. If you have any further questions, please contact Dorothy Nakama of my staff at this address or at (202) 366-2992.

Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:214
d.10/1/98