Easy to say, hard to do.

Voters set Muni’s on-time goal at 85 percent, but the struggling transit agency has never met that performance level.

Muni’s poor performance had long plagued former Mayor Gavin Newsom when he was in office.

During the Board of Supervisors' third question-time session with the mayor Tuesday, Mayor Ed Lee called on Muni to improve this year.

“For the duration of 2011 I would like MTA to tackle issues than can be broadly grouped into three areas,” Lee said.

Among them: “Demonstrating real measurable improvements … specifically getting Muni’s on-time performance up to the voter mandated 85 percent.”

San Francisco voters passed Proposition E in November 1999, setting the on-time goal and requiring a report every two years on whether Muni is living up to its expected performance standards.