Traffic signals that are demand responsive to automobiles, through electromagnetic sensor loops embedded in the street, are great tools for moving traffic. They control the signal to give green time where it’s most needed, determine whether a motorist is waiting in the turn lane for the left arrow or sitting at a side street waiting to get out onto a busy highway.

But they’re not so great for bicyclists.

The lighter weight and relatively smaller scale of the metal in bicycle tire rims and frames sometimes present problems for cyclists trying to maneuver through city streets. The electromagnetic loops generated by the embedded wires have to be set at a level that will detect an automobile idling above it, but not so sensitive that it will also detect a large vehicle waiting in an adjacent lane. Getting false readings of where the traffic is located disrupts the signal phasing and traffic flow.

As many American cities, including Denver, move toward making the streets more bicycle-friendly, traffic engineers are tweaking the system so that cyclists can trigger green lights.

And in the Seattle suburbs of Redmond and Kirkland, they’re coming up with new pavement markings to help cyclists.

The new pavement marking shows a bicycle symbol with white blocks behind and ahead of it. Engineers place it on the asphalt in the optimum location for a bicycle to be detected. In the examples in those two cities, the markings have been painted just beyond the intersection stop bar.

The best place for a bicycle to be detected is near the embedded wire rather than in the middle of the loop.

Kirkland traffic engineers have placed the new markings at seven intersections. In Redmond, they are on 150th Avenue NE, along with shared-lane markings called sharrows showing bicyclists where they are to ride. The shared lane means cyclists can ride in mixed traffic with autos rather than marking a separate bicycle lane near the shoulder.

If cyclists stop on the markings, traffic engineers say they electromagnetic loop will detect it and give them their place in the signal cycle.