A Bay Area business group is calling on Caltrans to open a third eastbound lane on the Richmond-San Rafael Bridge in the afternoon to alleviate traffic in Marin.

A top official of the business-sponsored Bay Area Council — a public policy advocacy organization — who lives in Marin said the project needs to happen sooner rather than later.

“This project is an example of the Bay Area not being able to do something that it really should be able to get done,” said Sleepy Hollow resident John Grubb, chief operating officer at the council. “Transportation infrastructure is important to us and it’s important to the economy.”

Last week Assemblyman Marc Levine introduced a bill — Assembly Bill 9 — in an attempt to push Caltrans to open a third eastbound lane by the end of next month. Levine, D-San Rafael, believes that will help relieve the afternoon commute, which has created bumper-to-bumper traffic in Marin. Some of that backup has spilled onto northbound and southbound Highway 101.

Levine, Grubb and other supporters contend opening the third lane — which now is a shoulder — is a simple fix: just paint in a new lane until a more permanent solution is identified.

The bridge initially had three lanes when it opened in 1956, but when drought hit in 1977 a lane was closed so a pipeline could be laid across the span to bring water to Marin. When the pipeline was removed in 1978, the lane was converted to a shoulder, given light traffic.

“We see the traffic clogging up northbound and even southbound during the commute,” Grubb said. “Caltrans should be working for the drivers to make improvements.”

Caltrans officials said Friday the bill is being reviewed.

“It’s being looked at by headquarters,” said Caltrans spokesman Bob Haus, who said the current agency plan has the lane reopening in October 2017. “We have been working to see what might be done.”

Caltrans has noted simply painting in a new lane is not as easy as it sounds. The shoulder that would be used for a lane reduces in width from 10 feet on the bridge to just over 5 feet on land in Richmond, which would create a bottleneck for cars.

Caltrans also says the existing shoulder is used as a bike path as it comes off the bridge. That use would not be possible if the shoulder is widened for vehicle use, though supporters of a third lane like Grubb said bikers rarely use the path.

Data provided by the Metropolitan Transportation Commission shows traffic on the Richmond-San Rafael Bridge has increased about 13 percent over the past five years, likely spurred by the economic recovery and more jobs. Last month, 1,296,202 vehicles paid to cross the span, the highest monthly tally on the bridge seen in the past five years.

In 2011, 12.2 million vehicles crossed the bridge, then 12.4 million in 2012, 13.2 million in 2013 and 13.8 million last year, according to data that accounts for toll payers driving west into Marin. This year through July, close to 8.4 million people have paid to cross the span. Through the first seven months of last year 7.9 million crossed.

Levine’s legislation calls for the lane to open “no later than Sept. 30.” The fate of the bill should be known soon. It will have to be approved by Sept. 11 or be put off until next year.

“This bill is important,” Grubb said.