SALT LAKE CITY -- Utah traffic engineers say the number of collisions involving motorists ignoring traffic commands almost doubled in 2007.

Drivers caused more than 2,000 accidents by running red lights or stop signs, or by ignoring yield signs.

Salt Lake City Police Sgt. Joe Cyr said it takes him just five minutes of observation at an intersection to see a motorist running a red light.

Now, state engineers are installing more signs warning drivers of approaching traffic lights and rethinking how long traffic lights should stay yellow before turning red -- which in Utah is about four seconds.

The timing of a yellow light can be adjusted within three to six seconds depending on traffic speed and other factors including the incline of a road.

It's a crucial issue that can affect driver behavior, although it's not always clear whether a longer or shorter yellow light leads to more or fewer drivers running a red light.

One Utah transplant, Dani Reesor, 22, said yellow stoplights seem longer in Utah than where she came from in California. Reesor said she finds herself going through more yellow lights as a result -- and also because Utah doesn't have photo-enforced stoplights.

But engineers say yellow lights that stay on for shorter durations can leave more motorists in intersections after the lights turn red.

Orem transportation engineer Paul Goodrich said he thinks the Utah Legislature should reverse a decision in 2002 that prohibited the state or municipalities from monitoring intersections with cameras to nab violators.

Goodrich said a standing joke in Utah is that "green means go, red means stop and yellow means you better hurry."

"The camera enforcement for red lights is a relatively good way to educate people that yellow does not mean hurry up. It means to slow down and stop if you have the ability to do that," he said.

Across the country, motorists who run red lights cause about 218,000 collisions every year, said Mark Taylor, signal systems engineer for the Utah Department of Transportation.

The accidents most often involve drivers under 30 without passengers who are in a hurry to get somewhere, he said.

Taylor is a technical adviser on a national advisory committee looking at making the length of yellow lights more uniform among all states and cities. He said the committee is close to recommending a federal standard.

The duration of yellow lights in Utah will stay the same unless national research or federal regulators suggest a change, he said.

"We are really exact on how we go about setting the yellow time," Taylor said of UDOT, which owns 1,100 of the 1,600 traffic lights in Utah. "We do that for consistency and for the safety of the motorist."