The new barrier free system has been introduced from Aug 30th 2008 to the M50 in Dublin

Basically there are 3 different payment options for drivers using the M50:

Option 1. Do nothing : Your car registration number will be logged by cameras as you pass through the toll bridge/plaza. You will be liable for a €3 euro toll which you can pay online with a credit or debit card at eflow.ie or by telephone on 1890 50 10 50. Or payments can be made by cash or card at Payzone outlets (many newsagents and convenience shops)
You must pay before 8pm the day after you use the M50 otherwise penalty charges kick in.

Option 2: Register with eflow.ie for a number plate recognition account. You give them your vehicle details and either debit card or bank details. As you use the M50 your registration is logged and Eflow charge you automatically each month for all the trips you made. The toll is €2.50 for this option. No monthly admin fees or tags.

Option 3 - Use a Toll Tag
An electronic tag on the windscreen of your car is used to register your use of the M50 and toll charges of just €2 euro a trip are deducted from your toll tag account. The account is topped up automatically from your credit card or bank account.