SAN FRANCISCO (AP) — With the San Francisco Bay Area economy booming, a plan to build a second tube for BART trains under San Francisco Bay is getting renewed attention.San Francisco Mayor Ed Lee said last month he planned to begin a regional conversation about another Transbay Tube, and an Alameda official said at a recent workshop he was eager to work with BART on a new tube to bring the transit service to his island city, the San Francisco Chronicle reported on Sunday.BART trains currently only have one tunnel under the bay, creating delays when a train stalls or other problems arise. A second tube would allow BART to offer 24-hour service and increase the system’s capacity, supporters tell the Chronicle.“Having a second BART tube isn’t optional,” said San Francisco Supervisor Scott Wiener, who is also a member of the regional Metropolitan Transportation Commission. “We have to do this.