Interpretation ID: nht88-2.65

TYPE: INTERPRETATION-NHTSA

DATE: 07/11/88

FROM: LOUIS F. KLUSMEYER -- SENIOR RESEARCH SCIENTIST, VEHICLE RESEARCH AND DEVELOPMENT, SOUTHWEST RESEARCH INSTITUTE

TO: TAYLOR VINSON--ATTORNEY ADVISOR NATIONAL HIGHWAY TRAFFIC SAFETY ADMINISTRATION

TITLE: NONE

ATTACHMT: ATTACHED TO LETTER DATED 08/15/88 TO LOUIS F. KLUSMEYER FROM ERIKA Z. JONES; REDBOOK A32(3), STANDARD 108

TEXT: Dear Mr. Vinson:

Southwest Research Institute (SwRI) has been asked to help determine the desirability of adding a "deceleration" or "pre-braking" warning light to the light configuration which is normally used on automobiles. As presently envisioned, this light woul d be amber in color and would be illuminated when the driver removes pressure from the accelerator pedal sufficiently to cause the automobile speed to start to decrease, due to the effect of engine compression, and would be extinguished automatically whe never the driver reapplies pressure to the accelerator pedal.

SwRI considers that a "deceleration light" of this type has the potential to reduce the incidence of automobile rear-end collisions (see Attachment 1) and that this potential is maximized if the light is located in as conspicuou a location as possible . The "best" location is considered to be immediately adjacent (or as close as possible) to the location of the "high-mounted stoplamp" since this location appears to offer the highest degree of visibility and would also serve to attract attention to th e high-mounted stoplamp area.

This location appears to have already been considered by NHTSA for this purpose, since it is mentioned as a consideration in FMVSS No. 108 on page PRE 137, and the principle is in widespread use on schoolbuses which use a manually activated flashing a mber light to warn that the red stop lights are about to be turned on and that all traffic must stop.

A review of FMVSS No. 108 (Lamps, Reflective Devices, and Associated Equipment) has failed to locate any requirement which would preclude locating an additional light adjacent to the high-mounted stoplamp; however, this type of requirement was conside red at one time (FMVSS 108, pages PRE 132-133 and PRE 135) and SwRI would like to find out if any requirement exists now, or is contemplated for the future, which would prevent the use of this location.

If I can provide further information or answer any questions which might expedite the answer to this question, please call (512) 522-3017.

Sincerely,

DECELERATION LIGHT MAXIMUM BENEFIT SITUATIONS The following three categories of driving situations are considered to be the situations in which deceleration lights would be of maximum benefit in reducing rear-end collisions.

HEAVY TRAFFIC (High speed/high traffic density with decreased vehicle separation distances)

High traffic density, with the associated decrease in visibility and increased need for enhanced reaction time, leads to a situation where reaction times become additive and eventually reach the point where a following driver is placed in a situation where his vehicle has exceeded its physical capability of stopping in time to avoid an accident. Deceleration lights offer the potential for minimizing this progressive lengthening of reaction time and thereby permitting long strings of cars to stop saf ely. Deceleration lights would also provide valuable information about adjoining lane driver intentions, particularly in lane change situations where an apparent opening in an adjoining traffic lane may be about to vanish if the driver of the vehicle at the front of the opening has decided to slow down and has taken his foot off the accelerator preparatory to stepping on the brakes.

MERGING TRAFFIC (Converging situations between vehicles entering or leaving limited access roadways)

A particularly volatile and rapidly changing situation occurs when two streams of traffic merge and the driver of the vehicle with the right-of-way is often forced to guess whether or not a merging driver is going to yield, speed up, or slow down. Th is guess is made harder by the fact that most drivers control their merging maneuver by use of the accelerator pedal only, and thus leave only the rate-of-change of their speed as a clue to their intentions. The driver with the right-of-way is almost al ways driving the faster, overtaking, vehicle and would be able to see a deceleration light which could furnish valuable clues about the other driver's intentions. A deceleration light would also furnish valuable information to drivers following the vehi cle with the righ-of-way if that driver decides to "let up on the gas" and give a merging vehicle more room to complete the merging maneuver.

DECREASED TRACTION (Braking situations where low traction may cause skids or other loss of control situations if brakes are applied too heavily)

Many drivers fail to realize the need for increased spacing between car during slippery conditions (rain, snow, ice, etc.). At the same time most drivers are taught that the proper way to slow down in slippery conditions is to let up on the accelerat or and allow the vehicle to decelerate gradually. This combination is likely to cause accidents involving following cars which do not realize that they are following a car which is slowing down until it is too late for them to make a controlled stop. A deceleration light would provide this information for following drivers and allow them to initiate their own stop, or speed reduction, in time to remain in control.