Regional transportation planners will meet soon with Sen. Dianne Feinstein and Rep. Mark DeSaulnier of Concord to discuss the two Democrats’ call for a study into building a new bridge between the East Bay and northern Peninsula or southern San Francisco.

The idea of a “Southern Crossing” that would carry both cars and rail transit has been discussed for decades but has never gotten off the ground, in part because of the cost. But the combination of ever-increasing traffic congestion and the call to action from two political heavyweights has planners once again sharpening their pencils.

“We have done this (study) in the past, and we would be happy to do it again,” said Randy Rentschler, spokesman for the Metropolitan Transportation Commission.

What planners and local politicians don’t want is any talk of a new bridge being part of Regional Measure 3, a planned June ballot initiative to raise tolls on the area’s seven state-owned bridges by as much as $3. The new money is already designated for a laundry list of less-costly traffic projects.

Adding the cost of new bridge would mean tacking another $5 to the toll hike — and pretty much doom its chances of winning the required majority voter approval in the nine Bay Area counties.

Meanwhile, private-sector groups like the Bay Area Council, Silicon Valley Leadership Group and the urban planning think tank SPUR are working behind the scenes on a wish list of other mega-projects.

In addition to a Southern Crossing, it includes a new Transbay Tube for BART, an underground high-speed rail line for downtown San Francisco’s new Transbay Transit Center, and a hub northeast of Livermore connecting BART, high-speed rail and the ACE train.

The combined price tag of all those big ideas is estimated at more than $100 billion.

“This is the big view,” said architect Jeffrey Heller, a member of the Bay Area Council business group. “It is absolutely essential to do this (study) to know what we need to do and what would be effective.”

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross