Interpretation ID: nht95-3.81

TYPE: INTERPRETATION-NHTSA

DATE: August 8, 1995

FROM: Eric D. Swanger, PE -- Engineering Manager, Specialty Manufacturing Co.

TO: John Womack -- NHTSA

ATTACHMT: ATTACHED TO 11/21/95 LETTER FROM Samuel J. Dubbin to Eric D. Swanger (A43; Std. 131)

TEXT: Dear Mr. Womack:

Research is performed at Specialty Manufacturing on a continual basis to investigate different means of improving upon the safety of school bus equipment. Recently, an inquiry has been made to Specialty concerning the usage of light-emitting diodes (LED 's) on stop arms. Apparently one state feels the usage of LED's to spell out the word "STOP" on the stop arm blade would increase the visibility of the sign in certain weather conditions.

After the engineering department of Specialty Manufacturing manufactured a prototype unit and tested the unit, several questions were raised which we feel need clarification from NHTSA in reference to FMVSS 131. The first being the basic viewing angles of LED's. While LED's have a quicker "on" and "off" time than incandescent bulbs, the overall viewing angle of an LED is extremely limited. Depending upon the placement of the LED's in the stop arm blade, the word "STOP" can vary from being noticeable to being a scattered pattern of lights. Exact placement of the LED's will depend upon the consistency of the manufacturing process. With incandescent lights, the light is very noticeable from all angles and manufacturing consistencies are not at all a concern.

The second issue is the legibility of the LED "STOP" at any given distance. Opinions of many casual onlookers asked to critique the LED sign when lit, seem to indicate that the letters are not large enough nor spaced far enough apart to be discernible at larger distances. Since the size of the letters is clearly defined by FMVSS 131, it appears that standard may have to be revised in order to ensure that "STOP" is legible at greater distances.

P2

The third issue is that of safety equipment consistency. Currently, all stop arms must have the word "STOP" displayed on the stop sign itself. The red lights are optional. The addition of another optional method of lighting may lead to confusion and s ubsequent passing violations due to visiting drivers being unfamiliar with state or county practices of school bus identification.

The development of an LED stop arm appears to our company to be quite expensive at the out set, and we are definitely concerned with the viewing angle, legibility from certain distances, and that consistences provided by FMVSS 131 could be in jeopardy.

I'm asking if you would please give us your interpretation of FMVSS 131 and the use of LED lights outlining the word "STOP." Specialty Manufacturing would be available to help in any standard research, manufacturer input, etc., as we have done in the pas t.

If I may be of any assistance, please do not hesitate to call me at 1-800-951-7867.