These lanes are designated for eligible vehicles to use for free, while others can use by paying a variable toll. As demand changes, the toll fluctuates to keep the optimal number of cars flowing at an acceptable speed. Toll cost is posted so motorists can decide whether to use the lane. Electronic toll collection (transponders) eliminates the need for toll plazas, allowing traffic to maintain highway speeds. Vehicles over two axles are prohibited from using both HOV and HOT lanes.   View Express Lane Sign Tutorial 

These lanes are similar to HOT lanes, with the main difference being that, in HOT lanes, vehicles that meet prescribed occupancy requirements are granted free access, while in ETLs all vehicles pay according to the toll schedule.