Nothing will change San Diego’s transit system in the foreseeable future so much as the Mid-Coast Trolley line, the $2.1 billion project that will extend the light rail system from Old Town to University Town Center.
Once it’s done, regional planners at the San Diego Association of Governments and Metropolitan Transit System will have more work to do to get everything they can out of the massive investment.
The project, first approved by voters in 1988, has been a long time coming. SANDAG is now short on funds , so it will be the region’s last light-rail extension for years, unless leaders figure out how to raise more revenue  for major projects.
There is, however, at least one low-cost way to make the project even more valuable to commuters – and that’s improving all the buses that feed into the new Mid-Coast line.
SANDAG and MTS can improve the timing and frequency of the east-west bus lines from the beaches and the inland areas around Clairemont that will bring riders to the new trolley line. The rail service, in turn, can bring them to jobs centers in UTC and downtown. Done right, it can improve the transit service for the entire swath of the city north of I-8 and south of La Jolla, rather than just the area along the new rail corridor.
Doing so is especially important because the Mid-Coast Corridor doesn’t fit the mold of an ideal rail corridor, despite the many jobs and amenities it’ll connect commuters to in UTC.
That’s because an ideal candidate for rail service is any corridor that already boasts a successful bus route, said international transit planner Jarrett Walker.
“The best case for a rail project is an overcrowded bus line,” he said.
The Mid-Coast corridor is not that. The current bus route between downtown and UCSD, the 150, carried just 2,700 weekday riders as of 2015 . That’s roughly a quarter the ridership of the 7 bus, which runs from La Mesa through North Park and into downtown, along University Avenue, a route that isn’t pegged for a light rail upgrade.
An MTS spokesperson, however, emphasized that ridership on the 150 has increased 47 percent in the last five years, suggesting a growing demand for transit service in the area. The combined ridership on the routes around UTC – the 201, 202 and 204 – is high, but there is little ridership between the university and downtown on the 150.
It’s not surprising that a highway bus route, like the 150, doesn’t get much ridership. Nobody likes to live, work or play directly next to a freeway. People prefer living and working a few minutes away by car, with easy access to the freeway. This means that there is little development within walking distance of a freeway bus stop. Moreover, just walking alongside the freeway right-of-way to reach the bus station is uncomfortable.
That brings up another obstacle facing the Mid-Coast extension: Most of the Bay Park and Linda Vista communities it runs through between downtown and UTC are not densely developed, offering little in the way of natural riders or additional destinations. The city is trying to increase development  there, but it hasn’t been easy .
But the line has opportunities to exploit, too.
For instance, bus lines on Grand Avenue and Garnet Avenue could both become strong connecting routes for the Mid-Coast. Residents there could suddenly have a viable commute to UTC or downtown on transit, if SANDAG and MTS make appropriate improvements to the bus routes.
The current bus route on Grand, the 30, is already the fifth busiest bus route in the region, with 6,800 weekday riders (the Garnet route, the 27, has only 1,000 weekday riders). Currently, it makes stops along Grand before turning south on I-5 and heading downtown as an express route; it also turns north when Grand hits Mission Boulevard and travels through La Jolla eventually to UCSD.
But the 30’s segment on I-5 is inefficient, making the entire route cost roughly $3.88 per passenger trip, above what you’d expect from one of the city’s busiest lines.
In effect, the 30 has a strong east-west segment on Grand, where it acts much like the 7 or the other high-performance urban buses, and then a weak north-south segment on the I-5, where it acts like the 150 and the other low-ridership freeway buses.
The 27 and 30 could then become major feeders, running between the trolley’s future Balboa Avenue station (at the intersection with today’s 27 route) and the beach. The trolley will run in the same right-of-way as the Coaster and Amtrak. Since it’s near the I-5, but not right in its median as with some light-rail lines (such as L.A.’s Green Line), waiting for the train would not involve as much highway noise as waiting for a bus in the freeway.
MTS would need to change the route of the 30 to feed the Balboa Avenue station. MTS did not respond to queries, but Bruce Appleyard , a professor of city planning at San Diego State, believes changes are likely.
“The trend is toward having a seamless transit system,” meaning a system in in which buses and the trolley complement each other, with easy transfers, he said.
Likewise, Appleyard suggested making transfers between the bus and trolley easier by timing them. The trolley’s Blue Line, which is what the Mid-Coast will be part of, comes every seven-and-a-half minutes, and the 30 bus comes every 15 minutes. If the 30 were cut to only connect the Balboa Avenue station through Pacific Beach and into La Jolla, it would be easier to time its arrivals with Blue Line trolleys.
Timed connections, though, are difficult. Walker, for instance, warns against attempting to time connections on buses that only run every 15 minutes. Traffic delays are just too disruptive.
Dealing with that issue, though, could be solved by providing queue jump lanes  to the buses, so they can skip backups at key intersections, Appleyard said. That’s less intrusive to cars than providing fully dedicated bus lanes, but could still increase reliability.
The main purpose of the Mid-Coast extension is not serving Pacific Beach, it’s providing faster service between downtown and the UTC and UCSD area. But Pacific Beach is an extra source of potential ridership, and improving the bus lines there could make transit usage substantially more convenient to a big chunk of the city where lots of young people live.
There is still cause for skepticism of the Mid-Coast trolley extension. The projected cost is still too high for the projected ridership, at $2.1 billion for 35,000 weekday riders. But the Mid-Coast region has a subtle strength in the layout of Pacific Beach’s street grid, which could lend itself to higher bus ridership.
The Mid-Coast trolley could be a chance to unlock that promise.