Electronic toll collection and toll rates
A nice article in NYT: Technology Eases the Ride to Higher Tolls citing important work by Amy Finkelstein of MIT on Tax Salience, the less you are aware of a tax, the easier it is to raise, this applies to tolls, so electronic tolls which have less salience than manual, result in the ability to raise tolls faster. Finkelstein's paper was cited in Levinson and Odlyzko's "Too Expensive to Meter:The influence of transaction costs in transportation and communication" earlier this year.