Below is a suggestion I made to the good people at Tesla. They requested I post it it to the teslamotorsclub forum because they're interested in seeing how much support there is from other people.
Elon Musk has talked a lot about safety being a priority and I'm very glad about that. But why do the Roadster and the Model S both have red turn signals at the back instead of amber?
The car already has two other sets of red lights at the back -- the red rear lights and the red brake lights. Having a third meaning for red lights at the back means that when another driver sees a red light at the back of your car, it takes their brain a split second to determine whether that's just a red rear light, or a red brake light, or a red signal that you're about to change lanes. The only visual difference between a driver tapping the brake pedal and a red turn signal is that with tapping the brake pedal both red brake lights blink together, whereas with a turn signal only one red light blinks, but discerning that difference is only possible if the other driver is able to see both the left and right light clusters at the same time. For example, a driver behind you one lane to the left in traffic may only be able to see the left cluster, not the right. When they see a red blink in the left light cluster does that mean you're slowing down, or that you're about to change lanes? The split second of extra time it takes them to realize it's a turn signal instead of a brake light could be, in some cases, the difference between an accident or not.
NHTSA reports I found on the web seem to support this intuitive reasoning. As is often the case with such studies, the effects can be small, and the causality sometimes unclear, but even if some might claim that the results are inconclusive, it's hard to understand why Tesla would not err on the side of safety.
Some quotes from "The Influence of Rear Turn Signal Characteristics (September 2008)":
The first analysis found a reduction of between 3 and 28 percent in the odds of being the struck (versus striking) vehicle in a turn-signal-relevant maneuver when the vehicle was equipped with amber versus red turn signals.it appears that amber rear turn signals are associated with a smaller odds of a being struck in a rear-end turning crash than red turn signals; likewise it also appears the LED-based turn signals are associated with a even greater reduction in odds of being struck compared with the odds found with tungsten light sources.use of amber turn signals may reduce the risk of rear end collision by about 22 percent.Some quotes from "Effectiveness of Amber Rear Turn Signals for Reducing Rear Impacts (April 2009)":Changing the color of a turn signal from red to amber appears to reduce the odds of being struck by 3 to 28 percent.
The principal finding of the report is that amber signals show a 5.3% effectiveness in reducing involvement in two-vehicle crashes where a lead vehicle is rear-struck in the act of turning left, turning right, merging into traffic, changing lanes, or entering/leaving a parking space. The advantage of amber rear turn signals is shown to be statistically significant.this study is consistent with the cited reports in finding amber turn signals significantly more effective than red turn signals.In Europe and many other countries, rear turn signals are required to be amber. Currently, manufacturers who produce vehicles for both the European and North American markets choose whether to produce all vehicles with amber rear turn signals or to equip the North American products with red rear turn signals. That is to say, the European regulations are more restrictive rather than being in conflict with FMVSS No. 108.And some other interesting comments I found on the web:The primary result is a 22-percent crash reduction for vehicles with amber turn signals (95% confidence interval 12% to 30%).
<http://mbz.org/articles/lighting/amber/>Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light
American regulators, alone in the world, have for decades dismissed the notion of restricting stylistic freedom with a requirement for amber, so automakers play with rear turn signal color as an insouciant styling gimmick in the NAFTA market: amber this year, red next year, back to amber at the next faceliftGiven that for other markets Tesla has to produce the Model S with amber rear turn signals, why not sell it with the same amber rear turn signals in the US also?If the driverís foot is on the brake pedal of a current Rabbit, Jetta, Passat, Sonata, X5, Q5, Accord coupe, Camry, or any of many other recent vehicles, his turn signal is practically invisible until youíre sucking his tailpipe. If heís getting on and off the brake while signaling, just forget about unscrambling a coherent message from his rear lights in the fractional moment available at speed in traffic.