Photo from FHWA.

Opponents of speed cameras often insist that they don’t want drivers to speed — what they object to is the revenue-raising function of the cameras and their invasion of privacy.  There may be a way to give these critics what they say they want, at least on some roads, while curbing excess speed more effectively.

How about wiring radars to turn the next traffic light red whenever a speeder passes? Instead of getting a ticket in the mail, a speeder would just get a red light.  With the right settings, this would slow down all speeders — including those who speed by less than 12 mph. 

Traffic safety experts I spoke with could not point me to any experience with such a system, so it will take trial and error to work out the bugs and optimize the design. 

Speeders’ behavior is more likely to change if they understand why they got the red light, but if drivers get that message too soon, they might speed up more to beat the light instead.

If a light turns green and then a speeder fairly quickly shows up, turning it red again, there might be pedestrians in the parallel crosswalk. They’ll need time to finish crossing, which would mean a 4-way red period. However, these will have to be minimal so that drivers are not overly tempted to run red lights.

And how would this work on multi-lane roads when one speeder might stop traffic for many other law-abiding drivers?  Signals always give some unnecessary red intervals — they can’t perfectly match changing traffic volumes through the day — but the red lights shouldn’t excessively interfere with vehicle movement. The first experiments should probably be on narrow roads with relatively light auto traffic.

There shouldn’t be legal obstacles. Radar-actuated traffic signals are approved by the Federal Highway Administration, and state laws that limit the placement of speed cameras do not apply to them. Some cities (including DC on parts of 16th Street) already limit speed with traffic signals by synchronizing closely-spaced lights so that drivers who exceed the limit hit a red. 

How and where might this strategy work best? And will objections to automated speed limit enforcement diminish when the radar system no longer raises revenue from drivers?