Signal Timing Is a Matter of Synchronicity

Dear Traffic Talk:

The traffic lights at Royal Hills Drive and Royal Oak Road in Encino had sensors that brought north- and southbound Sepulveda Boulevard traffic to a stop just long enough for side-street motorists to cross.

Motorists on Sepulveda also knew they would only wait a few moments.

Then, we watched in horror as a left-turn signal was installed for northbound Sepulveda traffic. The timing at the light was also changed drastically.

Susanna Modjallal

Encino

Dear Susanna:

The left-turn arrow was added for safety reasons, said Brian Gallagher, an engineer with the Los Angeles Department of Transportation traffic lights division.

The traffic lights timing changes are actually a synchronization project on Sepulveda stretching from Ventura Boulevard to Moraga Drive--geared at improving the flow of traffic on the heavily used thoroughfare.

Before the project, a single motorist exiting a controlled side street forced 20 to 40 cars on Sepulveda to stop.

Synchronization has reduced the southbound travel times in the morning by about eight minutes, said Gallagher. The northbound travel times in the evening have been reduced by 3 1/2 minutes.

The agency considers Sepulveda a major arterial route. Making it more efficient helps large numbers of commuters from the San Fernando Valley arrive to work and school on time. It also prevents drivers from using the surrounding neighborhood streets for shortcuts.

The long green times for traffic on Sepulveda--which services 3,000 vehicles an hour during peak times for the peak direction--result in long waiting times for motorists on the side streets. But three-minute waits have recently been cut by 50% at several residential streets, Gallagher said.

And once side-street drivers get on Sepulveda, they, too, benefit from the long green lights.

The signals are not synchronized during the off-peak hours and the wait on the minor streets should be less than 15 seconds when there are no cars on Sepulveda.

Meanwhile, Gallagher said the left-turn signal at Royal Hills was added after a study revealed that visibility was limited for motorists traveling in opposite directions because of a curve. Motorists would drive into the seemingly clear intersection and encounter one another at the last second.

The alternative to the left-turn arrow, Gallagher said, is to prohibit northbound left turns altogether.

Dear Traffic Talk:

Why not use double-yellow lines on the Ventura Freeway approaching exits to prevent last-moment changes from those in the fast lanes?

Von Whitsett

West Hills

Dear Von:

Markings used on roads and freeways have very particular functions. Double-yellow lines, for instance, indicate maximum restrictions.

According to Caltrans and California Vehicle Code rules, yellow lines are to separate traffic on divided roads.

The only exception for traffic traveling in the same direction is on freeways where the double-yellow lines are used to separate carpool lanes from the regular lanes.

Using them on freeway exits would create confusion and create a safety hazard, said Pat Reid, a Caltrans spokeswoman.

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