Dear Dr. Gridlock:

Montgomery County’s new refrigerator-size portable speed cameras have caused a predictable reaction. Now, if entering a surveilled 30-mph zone, some drivers slow down to 20 mph. When they drop speed abruptly, you can imagine the consequences.

— Michael Rae, Potomac

Montgomery has been using speed cameras for more than five years, dating back to when the enforcement technique was a pilot project for Maryland. The county’s program started with mobile cameras mounted in vans and added cameras fixed to poles. Now it also has 20 portable units, the things that look like green refrigerators.

County police think they may be more effective at chilling speeders than the pole-mounted cameras. Drivers learn those locations, slow for them and speed up, the theory goes. Move the cameras around within a certain corridor that is having problems with speeders and drivers may have no alternative but to consistently obey the law.

A report to the County Council’s Public Safety Committee in September noted that there’s no recent data on the effectiveness of the camera program. There was a 2009 report by the county’s Office of Legislative Oversight showing that 87 percent of drivers complied with speed limits within the camera enforcement areas. Crashes in those areas declined by 28 percent over the first year of the cameras’ use.

The placement of the mobile cameras may catch drivers by surprise, but the speed limit shouldn’t. County police say that at every location where there’s a camera, there’s a speed-limit sign in the same vicinity.

HOV enforcement

Dear Dr. Gridlock:

The lack of enforcement of HOV-2 regulations on Interstate 270 is creating a very dangerous situation. During the period when HOV is in effect, drivers cut in and out of the lanes to circumvent traffic and possible police enforcement.

They often illegally cross in and out where there are single or double solid white lines. I recognize that red-light and speed cameras are easier to enforce, but if the county and the state want to make roads safer, they need to focus on HOV enforcement.

— Don Weinstein, Rockville

The HOV lanes on I-270 and Route 50 in Maryland and on I-66 outside the Capital Beltway in Virginia are impossible to enforce. It’s too easy for drivers to slither in and out and too difficult for police to stop them.

Enforcement creates a hazard for police and for motorists. Cheaters look to pull out of the HOV lanes quickly. But even drivers who aren’t violating the rules slow down dangerously and get distracted when they see police cruisers.

This is one of the reasons I’m looking forward to the opening of Virginia’s 495 Express Lanes, set for Nov. 17. These lanes, free for carpoolers with at least three people aboard and the required E-ZPass Flex, were designed with better enforcement in mind.

The Flex is a specially designed transponder that can be switched to signal that the driver is claiming the carpool exemption. Virginia State Police can read that signal while their cruisers sit in areas cut out for them on the sides of the lanes.

The police have a contract with the lane operator, Transurban, to provide this enforcement. Transurban stands to lose money every time a driver cheats, ensuring a vigilance inspired by the profit motive.

We talked in last week’s column about those white bollards that will divide the express lanes from the regular lanes. While the bollards do have some give, they’re going to be vastly more effective than white lines at blocking drivers from weaving in and out of lanes.

This is a style of roadway management that Maryland should be looking at for possible use on I-270.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or e-mail