An overnight bus between the U.S.-Mexico border and downtown San Diego is so popular that local transit officials are making it permanent and planning new marketing efforts in Tijuana and on Spanish-language radio.

Local leaders are calling the border bus a great example of how transit can adjust to unconventional situations with innovative solutions.

Dubbed the “Overnight Express,” Route 910 covers essentially the same ground as the South Bay portion of the popular Blue Line trolley from 12:30 a.m. to 5 a.m. seven days a week.

The Blue Line can’t run during those hours, despite intense demand for overnight trolley service, because the tracks it uses are occupied by freight trains then.

That has left many early-morning workers and students who live near the border without a convenient and affordable way to get to downtown and other locations in the early morning.

Trying to solve that problem, Metropolitan Transit System officials began operating Route 910 as a pilot express bus last January.

While ridership took a few months to ramp up on the new route, Route 910 — which costs the normal MTS one-way fare of $2.50 — is now used by more than 7,000 passengers a month.

Perhaps more importantly, officials say it has reduced crowding on the first few Blue Line trains north from San Ysidro each morning.

“This is an example of creating something our customers need and actually want,” said San Diego City Councilmember Vivian Moreno, who serves on the MTS board. “It’s a model for how we can grow and adapt.”

San Diego Councilmember Sean Elo-Rivera, another MTS board member, said the overnight express helps people avoid having to pay for a taxi or Uber or asking a family member to drive them in the wee hours.

“This is a tangible way to improve folks’ lives — and very hard-working folks,” Elo-Rivera said.

The MTS board voted unanimously Thursday to make Route 910 a permanent express route.

The decision will cost $800,000 per year, but it won’t create budget problems because the route is already built into budgets for fiscal 2026 and 2027. Its funding comes from SB 125 — state legislation that devotes many millions to mass transit across the state.

The decision to make Route 910 permanent was based on strong ridership numbers.

Ridership during the six-month period from July through December was 31% higher than it was in the route’s first six months. During those first six months, an average of 191 people per day used Route 910. During the second six months, that had risen to 251 people per day.

Brent Boyd, director of planning and scheduling for MTS, said he expects those numbers to keep going up as more people become aware of Route 910.

“I’d expect that the ridership keeps growing gradually,” he said. “We see no reason for it not to.”

Mark Olson, director of marketing and communications for MTS, said the route was promoted during two waves of outreach — one last January and one in the fall.

MTS is also planning to advertise Route 910 on billboards in Tijuana and on Spanish-language radio. “We think there’s a lot of growth opportunity for this route,” he said.

Route 910 has better numbers than other MTS express buses based on its number of riders relative to how much it costs to operate. Officials called that remarkable when you consider the unusual hours that Route 910 operates.

Chula Vista Mayor John McCann, another MTS board member, said the success of Route 910 shows that we live in a 24-hour, seven-day-a-week society.

Boyd said it was surprising to see that the most popular bus on Route 910 is the second-to-last one before the trolley begins operating — not the last one.

“I think it’s because the last trip is close enough to when the trolley begins that people might just wait,” he said.

Route 910 doesn’t stop at all Blue Line trolley stations. It stops at San Ysidro, Iris Avenue, Palomar Street, 24th Street, 12th and Imperial, City College and Santa Fe Depot, taking less than an hour to finish its route.

Boyd estimated that about 60% of passengers board at San Ysidro and that roughly half are headed to downtown and the other half are headed to other stops.

To make the route permanent, MTS had to analyze whether it has had any adverse impact on low-income residents or ethnic minorities. The analysis determined that it hasn’t.

The agency says the population of the area served by Route 910 is 38% low-income, compared with 24% in the overall MTS service area.

The Blue Line, which was extended from Old Town to La Jolla and University City in 2021, carries 80,000 passengers a day. MTS officials believe it’s the second-busiest light-rail line in the nation.