How it might work.
Barrier-free or "open road" tolling is in use around the world, notably in Australia and Canada. It operates using scanners mounted on an overhead "gantry", which detect the presence of a transponder - usually called a "tag" - placed in the vehicle.
A tag?
Yes, a small device on the dashboard or attached to the windscreen which can carry pre-paid credit, like a mobile phone or the Luas smartcard.
Do vehicles have to go slow to have the tags read by scanners?
No, the current Eazy Pass system at the West-Link, for example, is programmed to read tags at speeds up to 120kp/h (75mph) although obviously because there is a barrier it does not operate at that speed. As vehicles join and leave the motorway, scanners will read the tag and determine the length of journey and the cost.
How many gantries?
Yet to be decided. Minister Martin Cullen, suggested a few, maybe four, which would allow motorists to pay for the amount of road they used. The method means scanners and gantries would have to be installed at every entrance and exit to the toll road. This would probably mean electronic tolls at all entrances and exits at 10 junctions, along 31km of the M50 between Sandyford and the M1.
What if a vehicle doesn't have a tag?
A single lane, with a barrier toll located off the main drag, will be provided for vehicles which do not have tags, such as foreign visitors or those who don't live close enough to use the road regularly.
What if a vehicle has no tag and simply drives through?
A photograph is taken of the licence plate, rather like a speed camera and legislation will be enacted to allow the gardaí to fine transgressors.