Furthermore, conditions are expected to worsen in the next couple of decades, said Angela Ruggiero, a SamTrans official who is working on the study. By 2040, both sides of the Bay are expected to experience an increase in the number of jobs and residents by 24 to 28 percent.

During peak traffic hours, say on a weekday at 5:30 p.m., traffic slows to as low as 4 miles per hour on Willow Road headed east, according to a map shown recently at a public meeting to discuss the issue. Heading eastbound on University Avenue, drivers clock 5 miles per hour, while eastbound Marsh Road averages 7 miles per hour. In the mornings, those average speeds in the other direction are hardly better.

Congestion on both sides of the Bay leading up to and across the bridge is a major barrier for getting around, many say, and the numbers bear it out.

Now, there is a study underway, with a price tag of $1 million bankrolled by Facebook, and an estimated completion time of 15 months, to evaluate how to ease transit between the Midpeninsula and the East Bay along the Dumbarton bridge and the right-of-way from the previous Dumbarton rail line.

Each day, about 77,000 cars pass over the Dumbarton Bridge. Commuters and locals alike know all too well how congested the roadways leading to and from the bridge can be.

At 1.63 miles in length, the Dumbarton Bridge between Menlo Park and Fremont is the shortest of the transbay bridges. To the south sits a defunct rail bridge that for decades has been studied for restoration.(File photo / The Almanac.)

The most recent activity on that idea was in 2011, when an environmental impact review on the Dumbarton rail bridge project was halted due to lack of funding, said Ms. Bartholomew. The report was never circulated. At the time, projections for ridership were low, while cost estimates for rebuilding the rail line ranged from $600 million to $800 million.

One option that has already been considered extensively is to revive the abandoned Dumbarton rail line as a commuter rail line, which could stretch from the Caltrain station in Redwood City to the BART station at Union City, according to BayRail Alliance, a rail public transit advocacy group.

Ms. Ruggiero said that the agencies participating in the study are looking into a wide range of options to address the transbay congestion, both in the near-term (by 2020) and the long-term (by 2030). According to Tasha Bartholomew, a SamTrans spokesperson, those agencies are the San Mateo County Transportation Authority, Alameda County Transportation Commission, AC Transit, the Dumbarton Bridge Regional Operations Consortium (which oversees the Dumbarton Express bus) and city agencies on both sides of the Bay.

In the short term, among the ideas for changes are making signaling adjustments on the vehicle bridge and to expand the bike and pedestrian path from East Palo Alto to Redwood City. That would be done to allow people on the Peninsula to more easily access the existing bike and pedestrian route over the Dumbarton bridge.

Long-term changes for the rail bridge could be the construction of bus rapid transit, light rail or electric trains across the corridor. Other, less conventional modes of transit are up for consideration too, including a hyperloop, ferry, gondola and monorail, she said.

Possible long-term changes for the vehicle bridge include designated bus or carpool lanes, added general use lanes, or changes in tolling policies, among other ideas, Ms. Ruggiero said.

While the current study will consider ways that the Dumbarton rail line could be "rehabilitat(ed) and repurpos(ed)," it will also evaluate other ways to deal with congestion on the Dumbarton Bridge (Highway 84) and its connecting roadways, she said.

Maybe it is, maybe it isn't. But at least $1 million and 15 months of more effort will go into exploring options.

At the time, Sue Lempert, a member of the Metropolitan Transportation Commission, said: "As soon as the Dumbarton Bridge gets jammed up (with traffic), people are going to be asking what our options are, and Dumbarton Rail is the best option out there."

In 2008, $91 million of funding that had been intended for the Dumbarton project was reallocated to BART for its project to extend its East Bay route southward to the Warm Springs Station in Fremont.

In 2007 talks picked up again, when the Green Cities Task Force was launched. A subcommittee of the task force studied the possibility of the rail extension, and said it would be an environmentally sound measure to cut greenhouse gases. By that time, though, cost estimates for the project had ballooned to about $600 million.

In 2004 a bill was passed, called Regional Measure 2 or RM-2, that raised tolls on seven Bay Area bridges by $1 to fund projects that improve traffic flow across the Bay. About $135 million had been set aside for the project.

A letter dating from 2000 written by then-Menlo Park Mayor Mary Jo Borak laid out central concerns pertaining to bringing the rail line through Menlo Park. The letter said that grade separations  structures to separate the roadway from the train tracks  for Menlo Park's rail crossings should be included in the plans. Concerns about the potential for disruptive rail noise in eastern Menlo Park also surfaced at the time.

Yet, plans for the bridge continued. A 1999 Almanac story reported that based on the task force's progress at the time, "under the most optimistic scenario, concept plans could be completed this year and trains could start running in 2003." At the time, the project was estimated to cost only $120 million.

According to one estimate, the trains could move between 5,000 and 7,000 passengers per day, with the potential to double in 10 years.

The vision was this: six commuter trains, which would run between Newark in the East Bay and Redwood City on the Peninsula, and would connect to Caltrain on one side and BART on the other. (Earlier plans imagined nine trains each way, but those numbers were later reduced.)

Later that year, the "Dumbarton Corridor Task Force," made up of public agencies and private businesses on both sides of the Bay, and cosponsored by the San Mateo County Economic Development Council, began meeting to develop plans to rehabilitate the rail bridge.

In 1995, Caltrain did a study of the rail bridge and the feasibility of a commuter rail line, but decided there would be only a small market for the line.

The original Dumbarton rail bridge opened in 1910 and served rail traffic only. It was the first transbay bridge and was situated to the south of the current vehicles-only bridge, which was opened in 1927. Back then, it was only two lanes wide. In 1982, it was replaced by a four-lane bridge.

The idea of resurrecting a rail bridge, adapted for commuters, on the site of the original one, has been raised and dropped a number of times over the past several decades.

Dumbarton corridor revisited: A twist on an old debate