In Bowling Green, people can no longer tell how late it is based on the traffic lights.

Transportation studies have shown that the flashing red and yellow lights that occur late at night and early in the morning can actually contribute to accidents, prompting Bowling Green to change the way its lights operate.

According to a report on the Federal Highway Administration Web site, removing the “flash mode” from traffic lights caused a 78 percent estimated reduction in right-angle collisions and a 32 percent estimated reduction in overall collisions.

“Eighteen of 28 [traffic lights in Bowling Green] previously were in flash mode,” said Lori Tretter, assistant municipal administrator. So now Bowling Green has changed the signals back to regular operation at night.

From midnight to 6 a.m., however, when there’s not a lot of traffic, instead of making vehicles wait for the light to change, the system has changed to a “free mode.”

Beneath the traffic lights, a sensor (also called loop detector) alerts the signal a car is there, Tretter said.

“The free mode will stay green on the major approach,” said Brian O’Connell, the city engineer. “As a vehicle came up on the minor approach the signal would be tripped and the light would change.”

There was not one specific reason why Bowling Green switched from flash mode, O’Connell said. There was a review of the number of accidents in communities with and without the flash mode, and the latter proved to have less. Statistically, this is the safer operation for traffic signals.

The FHWA report also stated that some studies have shown that without the flash mode a “positive control is provided rather than leaving the driver to decide when it is safe to proceed into the intersection.”

But in Bowling Green, a year or two operating without flash mode would have to pass before enough data is gathered to prove if it is the safer method, O’Connell said.

The process of changing Bowling Green’s lights just started a few weeks ago. Changing a few at a time, a week later nearly all the lights were in free mode.

Those five or six intersections that still aren’t in the correct mode are only waiting for loop detectors to be installed.

While the goal is to get all the signals onto free mode, O’Connell said an installation schedule currently isn’t in place yet for those signals still operating on flash mode.