Turn signal colour
Until the early 1960s, most front turn signals worldwide emitted white light and most rear turn signals emitted red. Amber front turn signals were voluntarily adopted by the auto industry in the USA for most vehicles beginning in the 1963 model year, though front turn signals were still permitted to emit white light until FMVSS 108 took effect for the 1968 model year, whereupon amber became the only permissible colour for front turn signals. Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light. In North America the rear signals may be amber or red. International proponents of amber rear signals say they are more easily discernible as turn signals. U.S. studies in the early 1990s demonstrated improvements in the speed and accuracy of following drivers’ reaction to brake lamps when the turn signals were amber rather than red. American regulators and other proponents of red rear turn signals have historically asserted there is no proven benefit to amber signals. However, a 2008 U.S. study by NHTSA (the National Highway Traffic Safety Administration) suggests vehicles with amber rear signals rather than red ones are up to 28% less likely to be involved in certain kinds of collisions, and a 2009 NHTSA study determined there is a significant overall safety benefit to amber rather than red rear turn signals.
There is some evidence that turn signals with colourless clear lenses and amber bulbs may be less conspicuous in bright sunlight than those with amber lenses and colourless bulbs.