SACRAMENTO, Calif. — Transportation officials in Northern California are exploring what it would take to build a new rail connection between San Francisco, Sacramento and other Northern California communities.

The more than 3-mile-long Transbay Tube carries Bay Area Rapid Transit (BART) passengers between San Francisco and Oakland. BART officials have proposed building another rail connector between the two cities.

That connector could tie-in other city-to-city rail services in the region, double BART's capacity, ease traffic congestion, reduce delays and allow passengers to ride a single train to their destinations, according to BART.

“The Second Transbay Rail Crossing opens an opportunity for BART and for its transit partners to consider the possibility of sharing a Transbay Rail Crossing,” according to the BART website.

The transbay corridor connects San Francisco by bridges, ferries, and BART to the rest of Northern California. That megaregion as officials call it consists of 21 counties between Monterey, San Francisco, Sacramento and the Northern San Joaquin Valley.

There are several city-to-city rail services that operate in Northern California including Caltrain, Capitol Corridor, and Altamont Corridor Express (ACE). BART officials say these systems do not directly serve key destinations and do not connect well to other transit systems.

The Capitol Corridor rail service operated by Amtrak has lines that run between Auburn and San Jose. That service does not have a direct train line into San Francisco. Passengers wanting to reach the city must transfer to a bus or another form of transportation to reach the city.

“With a vibrant economy and a rapidly growing population in the Bay Area, the Transbay Tube is already feeling the constraints balancing high demand with its currently limited capacity,” according to the BART website.

BART officials presented their ideas for a new Transbay rail crossing in November at a joint meeting with BART leaders and the Capitol Corridor Joint Powers Authority. BART and its partners are looking into what rail investments may be needed in the future to improve connectivity in the region.