BART offered a nearly $100 million fix Thursday for an obstacle that commuters often encounter at the beginning or end of their rides: out-of-service escalators.

Many of the system’s rolling staircases are now 40 years old, creaking along well past their 25-year expiration dates. They’ve become reservoirs for syringes, rainwater and human waste that sticks to the wheels and gears. It got so bad at Civic Center in 2012 that BART had to call in a hazardous materials team.

So the Board of Directors voted Thursday to award a $96.5 million escalator replacement contract — the largest in BART’s history. Funded by Measure RR, the $3.5 billion general obligation bond that voters approved in 2016, the project will install and replace 41 downtown escalators at Embarcadero, Montgomery, Powell and Civic Center stations.

Twenty-two of those escalators stretch from station concourses to streets, while 18 extend from concourses to platforms. BART will add one escalator at the entrance near the Orpheum Theatre.

The contract delighted Board President Bevan Dufty, who described escalator repair as a “whack-a-mole” game and said it’s become more difficult to attract and retrain workers to do it.

He recalled meeting a young escalator repairman at Civic Center Station who had spent a year on the job, and was already thinking about quitting.

“During his first month of work, a man with a hatchet chased him out of the station,” Dufty said of the repairman. “I just don’t know why people fuss at these poor escalator repair people so much.”

Board Director Rebecca Saltzman said BART fields constant complaints about its malfunctioning escalators, particularly in the downtown San Francisco stations.

“Those are the most unreliable models, and they’re also the most heavily used,” she said. Salzman noted, further, that those stations are deep underground. It’s a real hardship for people to use the stairs, especially if they’re carrying strollers or luggage, or if they’re encumbered by mobility problems.

What frustrates people the most, said BART spokeswoman Alicia Trost, is when an escalator opens after being out of service for months — only to break down again the following week.

She attributes those mishaps to constant battering, vandalism, inclement weather and other forms of abuse. When parts fail, the agency has to have the components fabricated, since most of the machines are so old that their manufacturers are no longer in business.

The escalator retrofits coincide with a separate effort to build canopies over station entrances in downtown San Francisco — curved, glassy, futuristic coverings that help fend off the elements. These new architectural features will protect escalators from breaking down during the 10-year contract.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan