Scott James/The Bay Citizen

A bicyclist in traffic. The next big plan for bike lanes in San Francisco could mean eliminating traffic lanes, parking or both on busy stretches of Fell and Oak streets, the city's main east-west routes for drivers.

San Francisco drivers know that to travel east or west through much of the city, Fell and Oak Streets offer a rare path of progress: up to four lanes wide, one-way, fast-moving and laced with synchronized traffic signals, otherwise known as “light karma.”

The good times, however, could soon be over.

The San Francisco Municipal Transit Agency is in the early stages of a plan that could squeeze cars on these popular routes to make room for bike lanes — by eliminating travel lanes or by removing street parking spaces.

The project is emerging as the biggest showdown to date between automobile drivers and those who advocate greener travel options. And there are indications that the city is leaning toward favoring cyclists before fully assessing public opinion — a scenario that has derailed past bike lane projects.

Fell and Oak Streets link the bedroom neighborhoods on the city’s west side with downtown and Highway 101. The two streets collectively carry 67,000 vehicles daily.

“They are like freeways,” said Alan Miloslavich, manager of Falletti Foods, a local market. “It’s like a 20-block on-ramp.”

This video shows Oak Street during rush hour:

The project would add bikeways — wider than standard bike lanes with a buffer zone separating cyclists and moving traffic — between Baker and Scott Streets, connecting the Lower Haight’s popular Wiggle bike route with the Panhandle park.

Advocates say bikeways are safer for cycling, which has grown in popularity in recent years; some 7 percent of city trips are now by bike, according to the San Francisco Bicycle Coalition. The city’s Transit First policy, updated in 2007, calls for safer cycling conditions.

But there are fears that removing a travel lane will increase automobile congestion. Removing street parking is also problematic, because open spots are already rare. Morgan Fitzgibbons, leader of the Wigg Party, a cycling advocacy group, said he sympathized with the parking challenges — he has seen his girlfriend nearly in tears after spending 45 minutes searching for a spot — but he said cars had a negative impact on the environment and the bikeway should take precedent.