Express buses were too early or too late more than 30 percent of the time, according to an audit released Thursday by New York City Comptroller Scott Stringer.

That means riders waited longer -- an average of 10 minutes when they weren't on time -- to catch a MTA express bus to commute to their jobs or return home after work, for example.

"The wheels on the express bus may go round and round, but they're delaying riders all over town," Stringer said at a news conference outside City Hall as stuck-in-traffic express buses crept along Broadway.

The audit, which surveyed 12 routes at the first or last stops between October and December 2013, was started under Stringer's predecessor, John Liu.

Express buses mainly serve transit-starved stretches of the outer boroughs without subway lines -- including many near the Long Island-Queens border. A regular fare, $6.50, is more than twice the cost of local buses and subways.

About 75,000 commuters ride express buses every day, said John Raskin, executive director of the Riders Alliance, an advocacy group. "When your express bus is late, you're late to work, you're late to school," he said.

The departure delays are worst during the afternoon rush hour. The worst performing lines were the Staten Island-serving X1 and X17, which were off schedule about 35.9 percent of the time, according to the Stringer audit.

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Express bus schedules can be difficult to manage, given traffic and other factors.

The Metropolitan Transportation Authority, which runs the city's 65 express bus lines, said keeping to the schedule isn't the best metric for measuring performance, but rather how "evenness of service," or how long a passenger is kept waiting.

Using capital letters for emphasis, MTA spokesman Kevin Ortiz said in an email: "Our goal with ALL of our buses is to achieve faster travel times, more evenly spaced arrivals, and overall better service for our customers."