THE MBTA SPENDS A LOT OF MONEY maintaining its aging buses, but the transit agency does a good job of keeping its fleet on the road, thanks in large part to a large group of contingency vehicles that can be rushed into service when a bus requires repairs, according to an analysis by a consultant.

According to the study by Colorado-based CH2M, the MBTA spends $5.99 per bus maintenance mile compared to $2.13 at the Baltimore Maryland Transit Administration and $2.38 at the Chicago Transit Authority. Only New York, at $6.13, had a higher cost per mile than the MBTA out of the seven agencies compared.

Of the seven agencies, the T had the oldest bus fleet at 9.3 years, with the others hovering around 7 years old. But, according to the study, no other agency gets more miles between breakdowns than the MBTA, with an average of nearly 13,000 miles. The next closest was Baltimore, with just over 7,200 of what is termed in the industry as mean miles between failure.

Jeff Gonneville, the T’s chief operating officer, conceded the T’s strong performance on miles between breakdowns is due in large part to the T’s fleet of contingency buses. Gonneville said the T can pull a bus out of service for repairs and replace it with a vehicle from the contingency fleet, thus avoiding breakdowns.

“It masks the lack of scheduled maintenance programs,” said Transportation Secretary Stephanie Pollack.

Gonneville said the T has “about 100 buses” in its contingency fleet, which works out to about 10.4 percent of the 955 buses in its operating fleet. The consultant’s report, however, said the contingency buses represent 17.8 percent of the T’s entire fleet.

Even though the T has a strong record on miles between bus failures, its track record on other maintenance measures is not so good. The consultant’s report said the MBTA spends as much as 80 percent of its maintenance costs on “reactive” repairs compared to other transit systems spending less than half that rate because of better scheduled maintenance programs.

Gonneville said the MBTA is spending nearly twice as much per mile on unscheduled maintenance to keep the aging fleet running. “Although we are in more reactive mode, it doesn’t mean repairs aren’t being made,” Gonneville said.

The study found the MBTA, like many other areas of its operation, is overwhelmed in its maintenance facilities with far too few repair bays available in aging facilities. According to CH2M, the T averages nearly 14 buses for each repair bay, while the ideal ratio is 8.7 buses per bay.

Complicating the maintenance issues are the varied types of buses the MBTA runs on its route. Pollack pointed out there are 11 types of propulsion used, from regular gas and diesel to electric and hybrid, as well as natural gas. The study recommends accelerating online training programs for the T mechanics to keep them current on best industry standards.

The draft report, which will be finalized next month, recommends beefing up the budget for scheduled maintenance; expanding the Everett maintenance facility to accommodate heavy repairs; and strengthening warranty control to maximize manufacturer liability.

Jack Sullivan is now retired. A veteran of the Boston newspaper scene for nearly three decades. Prior to joining CommonWealth, he was editorial page editor of The Patriot Ledger in Quincy, a part of the...