East Windsor is one of 21 New Jersey municipalities that was ordered to suspend the issuance of summonses from its red light enforcement cameras Tuesday.

The state Department of Transportation made the call based on video evidence provided by cameras placed at intersections, officials said.

The decision to suspend the issuance of summonses was made because the legislation that authorizes the cameras under a pilot program requires a formula to determine the proper duration of the yellow light in a traffic signal that differs from the formula most state roads already use.

State officials said most yellow lights follow the legally required engineering and safety standards in the Manual on Uniform Traffic Control Devices, which requires a minimum duration of the yellow light to equal one-tenth of the posted speed limit on the approaching road.

For example, where the approaching road has a posted speed of 40 mph, the signal must display yellow for a minimum of four seconds. The DOT rounds up to the nearest whole second, so in instances where the approaching speed limit is 45 mph, the signal displays a yellow light for five seconds.

The formula in the legislation that determines camera program eligibility, however, requires an analysis of vehicle speeds as they approach the intersection where a red light camera installation is proposed.The formula requires a yellow signal of at least three seconds if at least 85 percent of the approaching traffic travels at speeds of 25 mph or less.

For each increase of 5 mph in vehicle speed above 30 mph, the minimum duration of the yellow light must be increased by 0.5 seconds, according to the legislation.

This requirement, officials said, is there to ensure that the traffic signal is timed properly to provide motorists with sufficient time to avoid a violation and fine by entering an intersection when the light is red.

Under the state's directive, municipalities must conduct traffic analyses and submit certifications to the DOT by Aug. 1.

If the analysis shows that the duration of a yellow light meets the minimum duration as required by the legislation, a municipality will be permitted to issue violation notices for violations that occur during the suspension period, and continue issuing violation notices.

If the analysis shows that a signal does not display a yellow light long enough to meet the formula in the legislation, that intersection will be removed from the pilot program.

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