SAN FRANCISCO -- San Francisco Mayor Gavin Newsom and San Francisco Municipal Transportation Authority Director Nathaniel Ford said Tuesday that recent Muni accidents, including a streetcar crash that injured six people Monday evening, are unacceptable but insist the transit system is safe.

"It is safe to ride Muni," Newsom maintained, but he acknowledged, "It has been a very frustrating few weeks."

In Monday's accident, a Nissan Pathfinder was apparently struck from behind by a Muni F-Market streetcar at Market and Noe streets, causing the sport utility vehicle to crash into the rear of a second streetcar and become sandwiched between the two trains.

"It appears to be that the operator was distracted by a customer who approached him with some information," Ford said. He said the accident is still being investigated.

Andrew Sartorius, 21, and his boyfriend Gene Cain, 35, both of Roseville, were on that streetcar Monday and said the operator had engaged in a lively conversation with a passenger for some time prior to the crash and appeared distracted.

Sartorius, who came to San Francisco with Cain to see the musical "Wicked," said people fell out of their seats due to the impact.

Sartorius was left with a bruised elbow and Cain, who had his arm around Sartorius during the crash, suffered a wrist injury.

On July 18, a Muni light rail vehicle crashed into another train at the West Portal station, injuring 47 people. The operator of the train told investigators he blacked out right before the accident.

The National Transportation Safety Board is still probing that incident.

Both Newsom and Ford called the accidents "unacceptable."

"Our hearts go out to those individuals who have been injured in these incidents," Ford said today.

"We are not emphasizing on-time performance vs. safety," he insisted.

"We've actually seen a dramatic improvement in the safety of the system," Newsom said. He said that since last year, Muni has actually had a "double-digit decline" in traffic incidents such as collisions and derailments.

Ford said that along with improved procedures, training and more street supervisors, the Muni board last month approved a new camera system to monitor drivers in order to be able to later review a driver's actions immediately prior to an accident.

The new system will be in all Muni buses by the end of September, but Muni is still working with the manufacturer to design a system for its light-rail vehicles, Ford said.