UDOT's electronic system replaces a sticker program that required drivers to pay a monthly $50 fee. Under the new system, drivers can purchase a transmitter for $8.75 and then pay per use of the express lanes. The department has said the system is designed to free up regular travel lanes during peak hours and keep traffic in the express lanes moving at a minimum speed of 55 mph.

"This truly brings traffic into the 21st century," said state Sen. Howard Stephenson, R-Draper. "People are more free to get to their destination when they need to."

For single drivers, the cost of using the lanes varies from 25 cents to $1 depending on the time of day. Sensors are installed on both sides of the highway, and drivers are tolled whenever they pass through one of four zones.

The system will also help police enforce carpool laws that are frequently violated by solo drivers. A light mounted behind each of the 36 sensors on I-15 flashes green when the charge goes through and red when it does not, indicating whether a solo driver has paid the required toll.

More than 6,000 Utah motorists have already registered for transmitters.