SAN DIEGO -- The number of robberies, assaults and thefts on the San Diego Trolley system rose slightly last year, Metropolitan Transit System officials announced Wednesday.

The MTS reported 173 serious crimes on the 53-mile system last year, an increase of less than one percent.

"While the 2007 rate increased slightly last year, MTS is still 23 percent lower than the incident rate in 2002," said MTS Chief Executive Officer Paul Jablonski.

For the year, there were .47 thefts, robberies and assaults per 100,000 riders, an increase of less than one percent from the .44 incidents per 100,000 passengers in 2006, according to MTS.

Forty-percent of the thefts and assaults were committed against trolley security staff or property, not passengers, according to MTS.

There was also one homicide in an MTS parking lot, one burglary, no rapes and no arsons during the year, officials said.

Jablonski said the trolley is "one of the safest systems in the country."

"Our riders are safe, but they should also always be aware of their surroundings and take precautions," he said. "And they should know that MTS will continue to implement programs and coordinate with the communities we serve to make our system even safer."

The San Diego Trolley carried nearly 37 million passengers in 2007.