"...the functional purpose of tail lamps is to indicate the vehicle's presence
and width. The functional purpose of brake lamps is to indicate braking."
- It would increase the visibility of vehicles in normal driving conditions
- It would give following drivers two distinct messages: Yellow = Vehicle. Red+Yellow = Slowing/Stopped Vehicle.
The study peformed measured reaction times (RT) of the two scenarios: red tail lamps vs. yellow tail lamps. Results indicated significantly faster reaction times when vehicles had yellow tail lamps.
The study made me think about how this would affect colorblind drivers. When I (red/green CB) looked at the images in the report, I could see the yellow tail lights much better than the red. For me, red tail lights often blend into the vehicle itself -- especially during day or dusk conditions.
But I was then concerned that the yellow tail lights might be too bright, and their presence would detract from the more important message the red brake lights provide: Slowing/Stopped Vehicle.
To take it another step, for a driver with true color blindness I don't know that it would matter - if the brightness of the colors was the same.
Just more to think about as the issue of color is addressed in the research community.
Reference: McIntyre, S.E. (2008). Capturing attention to brake lamps. Accident Analysis & Prevention, Vol 40(2). pp. 691-696.