DART-Tag is a microwave transponder tag about the same size as a tax disc. It is interrogated by an antenna each time the vehicle approaches. If the driver's account is in credit, the barrier opens automatically when the driver approaches. A green light means the account is healthy, amber means it is running low, red means the barrier will not open. When the required amount has been thrown in, the barrier will open.
Electromagnetic sensors determine the size and weight of the coins.
The ACM keeps records of each vehicle passing through the toll booth and these are fed to a central computer. There are 14 lanes on the North Plaza and 13 lanes on the South Plaza. DART-Tag users can use any lane. One lane in each direction is reserved solely for DART-Tags. Lots of other useful information about the crossing.