Voters in the three counties served by Caltrain passed a measure that will add a one one-eighth cent sales tax in each county to help the financially struggling rail system.

Measure RR will provide Caltrain an estimated $100 million annually for the next 30 years to help fund operations, including expansion of service and capacity, as well as major capital projects. The measure needs to pass by two-thirds among the ballots cast in San Francisco, San Mateo and Santa Clara counties.