Drivers in bike-friendly cities may be doing double takes as bicycle-specific traffic signals pop up alongside the traditional round red, yellow and green signals controlling intersections.

At least 16 U.S. cities, including Austin, Denver, Minneapolis, San Francisco, Seattle and Washington, have installed the lights, which feature a bicycle-shaped signal, according to an October study commissioned by the Oregon Department of Transportation and the Federal Highway Administration. The signals are common in Germany, Sweden and Australia, according to the study.

The reason for the new signals? Bicyclists can be at risk when entering an intersection on a yellow light that allows enough time for cars to clear the intersection, but not for bikes, the study found. Even traditional green lights may not allow enough time for a bicyclist starting from a stopped position to make it across. Bicycle signals can also help prevent collisions when a motorist is turning right and a cyclist is going straight, by allowing the cyclist a few seconds’ head start.

Some bicycle signals stand alone, while others are incorporated into regular traffic signals. Some are timed, while others are activated when a bicyclist approaches the intersection, the study found.

Gary Obery, Oregon Department of Transportation senior traffic engineer, said bicyclists have to obey the signals like any vehicle would a regular traffic light. He also said there is not a current national standard for these signals since their use is still growing.

"At some point they will appear in our national standards, but that process involves trying things out and seeing what works best," he said. At least two states have passed laws setting out rules and regulations for them. California was the first, in the early 2000s. Last year Oregon lawmakers approved Senate Bill 130, adding bicycle-only signals to the state's list of traffic control devices.

The signals are being used in cities that are trying to make streets more bicycle friendly and in intersections that are more complex, Obery said.

Chicago officials announced the city's first bicycle-specific traffic signal in August. Atlanta got its first bike signal in October. In November, Oregon's capital city, Salem, joined four other Oregon communities with bicycle traffic signals.

"It's a great progressive move that Salem is putting their first light in," said Brad Bahr, an avid cyclist who works at South Salem Cycleworks. "They are beneficial for motorists and cyclists," he said, adding that they also help cars to be aware of the bicycle traffic.

Salem resident Joel Cleland, 39, rides his bike two miles to and from work each day. His route takes him past the new signal.

"It's a lot quicker and easier to make my way through that intersection now," Cleland said. "I've never waited more than 20 seconds for the new light to turn green."

The bicycle signal cost $1,000 to install in Salem, according to assistant city traffic manager Tony Martin.