As northbound drivers zip along Northeast Loop 820 and enter a work zone in the massive North Tarrant Express project near North East Mall, the speed limit abruptly drops to 50 mph.
Sitting in a barricaded area near the freeway, an electronic sign posts the speeds of passing drivers -- and urges those who are over the limit to "slow down."
With major freeway projects under way across Tarrant County, electronic radar signs -- some temporary, some permanent -- are being used when police aren't around to write tickets.
Signs are also found on city streets where it's easy to speed or to warn drivers of sharp turns.
Several studies concentrating on the signs' effectiveness in work zones have shown that they can help reduce speeds -- but often for a limited time.
Along that section of Northeast Loop 820 last week, most drivers didn't appear to be paying any attention.
During one five-minute span, only one car, which was clocked going 48 mph, was traveling at or below the 50-mph limit.
While the electronic signs may slow down some drivers, plenty still ignore them, Hurst Assistant Police Chief Steve Niekamp said.
"It looks like accidents have gone up a little bit for us in that area," Niekamp said. "In a lot of them, they haven't hit another car. They've just run into the barricades where the lanes change."
Lara Kohl, a spokeswoman for Bluebonnet Contractors, which is building the North Tarrant Express, said three radar signs have been up for about six months in the project's 13.5-mile corridor.
Bluebonnet worked with the Texas Department of Transportation to lower the speed limit to 50 mph and believes that the signs have helped make it safer for the workers and the 170,000 drivers who pass through the construction area each day.
"We do think the radar speed signs have helped make drivers more aware of their speed," Kohl said.
Both the North Tarrant Express and the nearby DFW Connector have other public awareness campaigns in place, using billboards and bumper stickers to urge commuters to drive the speed limit and stay off their phones.
Sign location a key
A 2006 interim report for the Transportation Research Board found that mobile speed display trailers can reduce speeds anywhere from 2 to 9 mph depending on whether the road is rural or urban.
One of the authors of that report, Jerry Ullman, a research engineer at Texas A&M University's Transportation Institute, said the trailers work if used properly.
"You'll find that where they're used, you'll generally see a 2- to 5-mph average in reduction of speed," Ullman said.
"If they're used right, they can get even more. Some studies have shown up to 9-mph reduction in speeds.
"But there is some concern about a novelty effect. Once you get used to them, you may not see the same results."
Ullman said the signs are more effective if they're paired with traffic enforcement by patrol cars and if their location is varied.
Using the permanent message signs along freeways to warn drivers of upcoming work zones can also help.
"It helps if it's apparent they're entering a work zone that's under different conditions than what they're currently driving on, like a really significant lane shift," Ullman said.
"If you just put them up in the middle of a work zone, it's probably not going to be as effective."
Popular on city streets
Many cities have installed permanent signs, often to warn drivers of tricky-to-navigate streets or dangerous curves.
Southlake has five permanent signs and one mobile, and a police spokeswoman said they are an "effective tool" in getting drivers to slow down.
A permanent sign went up this year on Shady Grove Road in North Richland Hills, warning drivers of a 90-degree turn.
Last summer in Fort Worth, two permanent display signs were placed along a dangerous S-curve on Forest Park Boulevard where some residents have complained that excessive speeds have led to crashes.
The neighborhood associations for Mistletoe Heights and Berkeley Place have urged the city to put the thoroughfare on a "road diet": reducing Forest Park to two traffic lanes -- one northbound and one southbound -- with a turn lane in the middle.
While the city studies the issue, Fort Worth spokesman Bill Begley said, the electronic signs are viewed as a temporary solution.
A traffic study conducted in February -- before the signs were installed -- showed that 85 percent of Forest Park drivers were traveling between 38 and 40.5 mph where the limit is 35 mph.
After the signs were installed, a survey in late August found that the average speed of 85 percent of the drivers dropped to 36 to 37.5 mph.
But Jason Brown, a resident of the Berkeley Place neighborhood who has pushed for the road diet, believes that the impact of the electronic signs won't last.
"I think they're more of a Band-Aid," Brown said. "They're speeding because of the design of the street."
Brown, who crosses Forest Park to take his kids to Tillery Park, said drivers also ignore flashing crosswalk signs designed to protect pedestrians.
"I think the place where those electronic speed signs have the biggest impact is for people who don't drive those streets every day," Brown said.
Susan Pressley, a Mistletoe Heights resident, has a Flickr page of photos showing accidents along Forest Park.
She said the most recent accident, on Halloween night when a child was struck while trick-or-treating, shows that the electronic signs aren't enough to address the speeding problem.
Still, she hopes that the signs stick around.
"We could use all the help we can get to make this street safer," Pressley said.
Bill Hanna, 817-390-7698