Controversial bus lane cameras, labelled a "money-making racket", become operational in Belfast today.
After a two-week period of grace, drivers who flout the law risk a £90 on-the-spot fine.
Six static cameras have been installed at congestion hotspots in Belfast city centre, while a mobile unit will monitor the greater Belfast, Lisburn, Antrim and Newtownabbey areas.
Department of Regional Development (DRD) bosses have said the cameras are not intended to generate income but they have already estimated that they will issue around 15,000 fines a year - more than 40 a day. This would amount to £500,000 in fines every year.
Transport Minister Danny Kennedy said: "The advice is simple, observe the bus lane restriction and avoid the possibility of a fine."
Bus lanes have been the subject of hot debate since they were introduced in Belfast in October 2012. Legislation passed earlier this year permits the DRD to monitor vehicles using bus lanes and deal with an infringement as a civil offence.
Mr Kennedy added: "Bus lanes were introduced to help manage traffic, reduce journey times and improve our public transport infrastructure. Supporting this, I want to ensure that everyone who travels on our roads does so in a responsible and respectful way. I am confident these new measures will help achieve this."
In Belfast, cameras are situated at Castle Street, East Bridge Street, Donegall Square East, Donegall Square South, Great Victoria Street and College Street East. The new system has cost around £200,000 but the DRD expects to generate around £500,000 a year to be reinvested in the public transport network.
The £90 fixed penalty fine will be cut to £45 if paid within 14 days. There will also be an appeals process. Public hire taxis and emergency vehicles will be exempt from fines.
Hitting out at the cameras when they were announced last month, DRD committee member David McNarry said: "It's about time motorists were given a break. In fact, bus lanes cause the most congestion and should be withdrawn from service completely and an end put to all this nonsense."
The Ukip MLA added: "It's bad enough having to drive through Belfast without having to worry about cameras and fines.
"This is just a money-making racket, another tax on hard-pressed motorists. It will also be a visitor's nightmare. We are trying to attract tourists and then we'll just slap them with a fine if they stray into a bus lane."