In general, tolling involves the imposition of a per-use fee on motorists for a given highway facility. Historically, these fees have generally been flat tolls that may vary by number of axles and distance driven, but not by time of day. Their primary purpose is to generate revenue.
Information on tolling activity at the state and local levels is providing in FHWA's Toll Facilities in the United States report. It contains selected information on U.S. toll facilities that has been provided to FHWA by the States and/or various toll authorities. The report identifies toll facilities in operation, financed, or under construction as of January 1, 2015. The report is based on voluntary responses received biennially and may have inconsistencies, omissions, or errors.
Further discussion of tolling as a revenue source from the state and local perspective is provided at BATIC Institute: An AASHTO Center for Excellence. The BATIC website also provides a State-by-State Map of state-, locally-, and privately-operated toll roads in the United States.
The IPD Revenue Project Profiles provide numerous examples of pricing involving tolling.