Double-decker buses, now the province of tourists and tech workers in the Bay Area, will soon be coming to the workaday world of East Bay transit riders. AC Transit plans to roll out a modern double-decker bus Monday to begin a three-week test on a variety of routes.

The idea is to see whether the two-story transit vehicles work as well, or better, at hauling heavy loads of passengers than the extra-long articulated buses that resemble an oversized accordion on wheels. The two-level bus seats 80 people, compared with 57 on tour-bus-like commuter coaches, 52 on articulated buses and 36 on standard 40-foot buses.

AC Transit has seen an increase in ridership the past two years, especially on its transbay routes, and sometimes has to make passengers wait for the next bus.

“We have been operating Transbay service for more than 50 years, and we want to look at what is the best vehicle that best fits us now,” AC Transit General Manager David Armijo said in a statement. “We’ve tried a lot of different kinds of coaches. But, until now, we haven’t tried this one.”

The 42-foot-long double-deck bus, with a height of 131/2 feet, will make its maiden voyage Monday morning on the U-line, traveling between Fremont and Stanford University across the Dumbarton Bridge.

The bus will also operate on the FS, L, NX, NX1 and NX2 transbay routes and spend several days on the busy 51B line between the Rockridge BART Station and the Berkeley Marina. Rides on the double-decker bus during the test period will be free. Schedules are available at www.actransit.org/double-decker-bus-pilot-schedule/

“We want as many people as possible to board it, ride it and, most importantly, give us their feedback,” said Clarence Johnson, an AC Transit spokesman.

AC will also look at how two-level buses affect the amount of time spent at stops, how easy it is for passengers to navigate the stairs, and how the bus handles in traffic and pulling in and out of stops. But customer acceptance will play a big role.

“Even if all went well, and we got horrendous feedback,” Johnson said, “we wouldn’t put them into service.”

The transit agency, which operates buses in the western portions of Alameda and Contra Costa counties, has been training a group of drivers and taking the bus out for road tests. Passengers will be asked to heed some extra rules while riding: remain seated on the upper level and don’t use the stairs while the bus is in motion.

After the three-week test, AC staffers will tally results of customer surveys, gather the opinions of drivers and mechanics, and make a recommendation to the transit district’s directors.

“There’s no time frame yet,” Johnson said. “But we’re not talking years, we’re talking months or maybe even weeks. We really want to get a high-capacity vehicle in place as soon as possible.”

But soon is not necessarily fast. Should AC Transit decide to go with the twin-level buses, the agency would have to solicit bids then award a contract — a process that takes months. Then it would take 12 to18 months for the buses to be built and delivered. The earliest double-deckers would join the AC Transit fleet would be 2017.

AC Transit would be the first Bay Area public transportation operator to run double-decker buses, Johnson said. And while they’re a fixture in London, and common in other European countries, they’re still relatively rare in the U.S. Transit agencies in Seattle, Davis and Las Vegas regularly run double-decker buses similar to the model being tested.

Michael Cabanatuan is a San Francisco Chronicle staff writer. E-mail: mcabanatuan@sfchronicle.com Twitter: @ctuan