The mere possibility that a SF County Transportation Authority study could result in a 'border' charge (congestion toll) to drive into SF from San Mateo County has the latter floating their own competing toll for motorists entering San Mateo County.
Dec 14, 2010 San Jose Mercury News
San Mateo County officials have a bone to pick with their bigger neighbor (in population, not area) to the north, San Francisco: don't charge us to drive there. Unlike drivers from East and North Bay counties, no bridge tolls separate the counties.
Dec 3, 2010 The San Mateo Daily Journal
Three possibilities for tolling San Francisco's downtown have been advanced by the Board of Supervisors; two involve tolling the 'Southern Gateway', the only entrance to the peninsula city that is untolled. However, Prop 26 could doom the plan.
Nov 15, 2010 San Francisco Chronicle