The Transportation Authority of Marin commissioned the $30,000 study to get a better understanding of Marin’s travel patterns. More specifically, the agency wanted to examine the origin and destinations of commuters on Highway 101 at the Marin-Sonoma county line, Highway 37, the Richmond-San Rafael Bridge and the Golden Gate Bridge.
“It’s data we will use over time for planning,” said Dianne Steinhauser, executive director of the Transportation Authority of Marin.
The data was gathered from cellphones and GPS units that communicate with mobile networks when in use and while idle. The mobile device data is then analyzed as the units move with drivers and driving patterns are established. Only mobile signals are tracked, not the user’s identity, according to the transportation agency.
The data, which will be presented to the Transportation Authority of Marin board Thursday night, shows that 36 percent of traffic flowing into Marin from other counties during the morning peak commute — 6 to 10 a.m. — comes from the East Bay.
“We have more people coming in from the East Bay than we do from Sonoma (28 percent),” Steinhauser said.
In general, more people have begun using the Richmond-San Rafael Bridge in recent years. Some 29.4 million drivers used the span in 2016, a 1.6 increase over the prior year. That means another 500,000 people drove the span compared with 2015. Over the past five years, traffic has increased about 13 percent.
Those who come to Marin also have to go home, which has led to bottlenecks getting to the span in the evening. As a remedy, transportation officials are working to open an eastbound third lane on the bridge that should open by November.
“That increase in people on the bridge is related to the explosion in the economy that we saw in the 2012 to 2015 time period,” said John Goodwin, a spokesman for the Metropolitan Transportation Commission, the agency planning the lane expansion. “The growth rate has not been as robust recently, but the numbers are still up and we are working to accommodate those people.”
The data also shows a strong reverse morning commute — 28 percent of drivers from other counties — into Marin from San Francisco and points south over the Golden Gate Bridge.
“It’s surprising to see the amount of people coming over the Golden Gate into Marin in the morning; it’s a lot heavier than it has been,” Steinhauser said. “It used to be easy.”
Golden Gate Bridge traffic in general is on the upswing, with roughly 41.5 million people driving the span in 2016, up 2.3 percent from the prior year.
Kary Witt, who has been Golden Gate’s bridge manager for 18 years and monitors traffic, said the strong reverse commute is relatively new.
“More and more there has been a demographic change in the counter commute,” he said. “Many more south of the bridge work in the North Bay compared to 10 years ago. That impacts the evening southbound commute over the bridge ... which can be very heavy.”
The data also shows the roads in Marin are busier during the afternoon commute, from 3 to 7 p.m. About 13 percent more trips occur during the afternoon peak period, with a majority of those trips starting and ending in Marin. In addition to commute trips, shopping, school, recreational and visitor trips are in the mix.
Trips starting and ending in Marin during peak morning and evening commute times comprise about 72 percent of traffic, while 24 percent of those driving are going to or coming from Marin. Those passing through the county to other destinations make up about 4 percent of traffic.
“There was some thought that in the evening people were leaving San Francisco, passing through Marin and going to Contra Costa, but the data shows that is not really the case,” Steinhauser said.
©2017 The Marin Independent Journal (Novato, Calif.) Distributed by Tribune Content Agency, LLC.
