As thunderstorms rolled across the D.C. area Monday evening, drivers on the Capital Beltway in Silver Spring may have noticed flashes in the sky. It wasn’t necessarily the lightning. It may have been a speed enforcement camera getting its first work out in the work zone at the Northwest Branch bridge.

The warning signs, posted a bit prematurely when the bridge reconstruction project was just getting started in early June, are visible again, and the mobile camera is working. The Maryland State Highway Administration has not reduced the 55 mph speed limit. So to get a citation from the camera, drivers will have to be doing at least 67 mph through the narrowed, shifting lanes of the work zone.

While the camera is active, speeders will get warnings through Aug. 21. After that, the owners of vehicles captured on camera while going at least 12 mph over 55 will receive $40 citations. It's best to start practicing now.

The Northwest Branch bridge work zone between University Boulevard and New Hampshire Avenue becomes one of the first two sites for enforcement cameras on the Beltway.

While the lengthy rehabilitation project on the bridge has been underway since the spring, the highway administration has just started a resurfacing project on the Beltway’s inner loop (I-95 South) between the D’Arcy Road bridge and the Branch Avenue (Route 5) interchange in Prince George’s County. That project is scheduled to continue for three or four months.

Drivers in this work zone also will encounter Maryland’s mobile speed cameras, highway administration spokesman David Buck said Tuesday. The speed limit remains 55 mph. As at Northwest Branch, a three-week warning period began Monday, after which $40 citations will be issued to vehicle owners.

This work zone will be a bit different from the one in Silver Spring, where the workers usually are behind concrete barriers. In the resurfacing project, the workers are separated from motorists only by orange barrels or cones.

Any work zone is dangerous, and it’s especially dangerous for the motorists, even though they’ve got all that metal around them.

Buck said before and after studies of the highway administration work zones show that camera enforcement has been effective in slowing down many motorists. He said there’s been about a 50 percent decrease observed in vehicles driving more than 10 mph over the posted speed limit.