Interpretation ID: nht93-3.29

DATE: April 29, 1993

FROM: Bob Jones -- Director of Engineering, Independent Mobility Systems, Inc. (IMS)

TO: Mary Versailles -- Federal Transit Administration, U.S. Department of Transportation, NHTSA

COPYEE: C. Flanigan; G. Anesi; R. Dumas

TITLE: Re: Compliance to FMVSS 220 with a Raised Roof Minivan

ATTACHMT: Attached to letter dated 6-18-93 from John Womack (Signature by Ken Weinstein) to Bob Jones (A41; Std. 220)

TEXT: Although School Bus Rollover Protection does not apply to minivans, many states and/or municipalities are including this requirement in their bids for vehicles which are equipped to serve the handicapped.

We have tested and met the requirement with the OEM roof; however we are now faced with a new challenge as we are being asked to make available a raised roof model. We know how to build the roof, how to reinforce it with a cage, but what we don't know is how to do a FMVSS Bus Rollover Test.

I am enclosing a drawing of our prototype roof, including its steel cage support system and a photo copy of an installed roof. As you can see from the drawing, the raised roof starts at the 'A' Pillar with a plus 2.0 inches, builds up to 4.0 inches then 9.0 inches and finally at the 'D' Pillar it is plus 12.563 inches.

I have included excerpt pages from the FMVSS 220 Laboratory Test Procedure which, I believe, demonstrates our need for an interpretation as to how we should meet the legislation with this raised roof configuration.

Because we are less than 10,000 pounds GVW, our force plate will be 5 inches longer and 5 inches wider than the van roof. We must keep the force plate transverse axis level and make contact with the roof at not less than two points. The longitudinal axis of the force application plate may deviate from the level or horizontal position; however, deflection readings are to be taken as close to the four corners of the force application plate as possible and then extrapolated to provide corner readings.

When we evenly distribute the vertical force, we are going to get an unusual load path. The compression is going to be in the 41 inches to the rear of the 'B' Pillar. We would almost need a complete collapse of the roof before the load cylinders located at the front outboard positions on the plate register.

After reviewing the enclosed material, we would be most appreciative if you would offer us your interpretation of how we can satisfy this standard in a meaningful way.

I will be out of the country from May 4 to May 25. In my absence, you can address any questions or correspondence to Mr. Rocky Dumas at our New Mexico headquarters.

I thank you for your consideration and look forward to discussing the subject with you upon my return.