In some urban settings, automated gates are in use in electronic-toll lanes, with 5 mph (8 kph) legal limits on speed (and 2 to 3 times that as practical limits even with practice and extreme concentration); in other settings, 20 mph (35 kph) legal limits are not uncommon. However, in other areas such as Houston, Texas, cars do go through electronic lanes at full speed. Enforcement is accomplished by a camera which takes a picture of the car and sends a fine to cars that pass through without paying a toll.
Factors impeding full-speed electronic collection include:
Despite these limitations, however, it is important to recognize that throughput increases if delay at the toll gate is reduced (i.e. if the tollbooth can serve more vehicles per hour). The greater the throughput of any toll lane, the fewer lanes required, so expensive construction can be deferred. Specifically, the toll-collecting authorities have incentives to resist pressure to limit the fraction of electronic lanes in order to limit the length of manual-lane lines. In the short term, the greater the fraction of automated lanes, the lower the cost of operation (once the capital costs of automating are amortized). In the long term, the greater the relative advantage that registering and turning ones vehicle into an electronic-toll one provides, the faster cars will be converted from manual-toll use to electronic-toll use, and therefore the fewer manual-toll cars will drag down average speed and thus capacity.
These factors herald more, and more effective, use of electronic tolls.