Surveys of rear lighting system malfunctions on passenger cars and light trucks showed that about 4% of vehicles with single compartment rear lamps had an inoperative presence or stop/turn lamp, while less than 1% of vehicles with multiple compartment rear lamps had at least one operating presence lamp compartment working on each side, and about 2.5% had no stop/turn signal lamp compartments operating on one side. Thus, although the frequency of failure of bulbs or circuits was greater in rear lighting systems with multiple compartment than single compartment lamps, the likelihood that at least one presence or signal lamp compartment will be operating on each side of the vehicle is greater in lighting systems with multiple compartment lamps, by 2-3%.
The effects of some rear lighting system malfunctions on the ability of drivers to identify signals was evaluated in two experiments using a driving simulator. Six rear lighting systems using combined function, separate function, signal lamp redundancy, and color coding were compared in normal and malfunctioning operating conditions.
It was concluded that the use of signal lamp redundancy offers only a minor benefit in terms of driver performance. In other respects, those rear lighting systems employing separation of function provided better performance of drivers. One system using stop signal lamp redundancy and separation of function provided effective detection of stop signals. The most effective systems used color coding and functional separation of signal lamps. It was suggested that vehicles with multiple compartment signal lamps employ variable-load flashers. However, communication of braking and turning can best be accomplished by functional separation and color coding in vehicle rear signaling systems.