Memorandum - NHTSA

v-11
During the development of an NPRM for vehicles with wheelchair lifts (previously called
FMVSS No. 401), the agency proposed a procedure for measuring platform resistance in whkh a
loaded power wheelchair would be placed on a wet, 30 degree inclined lift surface until sliding
occurred. This was believed to occur at about a 0.60 coefficient of friction (COF).
Unfortunately, testing at VRTC (Docket No. NHTSA-98-45 11) revealed that this was not an
effective method because, in many cases, the wheelchair tipped over before sliding could occiir.
Subsequently, VRTC staff conducted a literature search to determine other test procedures, wl iich
might be useful in determining slip resistance and selected ANSVRESNA WC13 - 1991
Determination of Coefficient of Friction of Test Surfaces for further investigation. NHTSA
proposed the ANSYRESNA WC13-1991 coefficient of hction (COF) test procedure with the
following modifications:
Procedural Changes to ANSYRESNA WC/13:
1. The test surface area 450 X 100 mm (17.5" X 3.94") is horizontal and clean from dust, dirt ind
debris.
2. Pull the test block by a mechanical means to achieve a pull rate of 20 +/- 2 mm/s.
3. Pull the test block for a minimum of 13 seconds and use only the last 10 seconds of force d;i.ta
to calculate the average force, which is to have 2% accuracy in the 25N - 100 N range.
4. Collect force data at a frequency of >= 10 Hz.
5. The link between the test block and pulling mechanism shall have a stiffness>= 1 X lo5N/ItI.
6. Evenly spray 3 ml(O.10 02.) of distilled water per 100 cm2(15.5 in2) of test surface area.
Begin the test within 30 seconds of the water spray.