Electronic toll collection

Electronic toll collection (ETC), an adaptation of aircraft "identification friend or foe" technology, aims to eliminate the delay on toll roads. It determines whether the cars passing are enrolled in the program, alerts enforcers for those that are not, and debits electronically the accounts of registered cars without their stopping, or even opening a window.

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:

• significant non-participation, entailing lines in manual lanes and disorderly traffic patterns as the electronic- and manual- collection cars "sort themselves out" into their respective lanes
• problems with pursuing toll evaders
• need, in at least some current systems, to confine vehicles in lanes, while interacting with the collection devices, and the dangers of high-speed collisions with the confinement structures
• vehicle hazards to toll employees present in some electronic-collection areas
• in some areas at some times, lines even to pass through the electronic-collection lanes

Even if line lengths are the same in electronic lanes as in manual ones, electronic tolls save registered cars time: eliminating the stop at a window or toll machine, between successive cars passing the collection machine, means a fixed-length stretch of their journey past it is travelled at a higher average speed, and in a lower time. This is at least a psychological improvement, even if the length of the lines in automated lanes is sufficient to make the no-stop-to-pay savings insignificant compared to time still lost due waiting in line to pass the toll gate.

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.