The City of Burbank uses two types of left turn signals, "protected" and "protected/permissive," at City intersections. Drivers often question the operation of the protected/permissive left turn signals and sometimes express confusion about their operation. The best type of left turn signal operation depends upon the amount of turning traffic, driver visibility, traffic speeds, and accident patterns.
Protected Left Turn Signals
Drivers are accustomed to seeing left turn signals that operate with a green arrow which is followed by an amber arrow, then by a red arrow. Drivers are allowed to complete left turns on the green arrow free of any other conflicting traffic; then the amber arrow warns turning drivers that the left turn signal is ending. The red arrow shows that left turns are not permitted. This type of left turn signal is called a "protected" left turn signal, because the left turn movement is always protected by the turn signal.
Protected/Permissive Left Turn Signals
Over a decade ago, the City of Los Angeles began using "protected/permissive" traffic signal operations for left turns. A five-section left turn signal is used to show the usual green arrow for a fully protected movement, which is then followed by the amber warning arrow. After the amber arrow has terminated, a solid green ball signal is shown, with no red arrow. The solid green ball allows the through traffic movement to proceed unopposed, and left turns can be made when there are adequate gaps in opposing traffic to complete left turns safely. This is the "permissive" part of the left turn operation.
The "protected/permissive" type of left turn phasing is designed to help minimize delays by eliminating the red arrow and allowing vehicles to turn on the green ball after opposing traffic has cleared. Elimination of the red arrow improves efficiency of the intersection because motorists do not have to wait to turn left when there is no opposing traffic. This operation is best suited for non-peak traffic when traffic volumes are low, and the "protected/permissive" left turn signal still provides a green left turn arrow during high traffic hours.
Advantages of Protected/Permissive Left Turn Signals
The advantages of this operation when compared to fully protected phasing only are:
- Reduced delays because left turn drivers may have an opportunity to make their left turns during the green interval.
- Use of a shorter signal cycle length in coordinated systems through a reduction in the time of the fully protected green interval for the left turn movement.
- Reduced chance of disturbing traffic in adjacent lane as left turn queues are less likely to exceed the length of the left turn lane.
For more information regarding left turn signals, call the Traffic Division at (818) 238-3915.