The College Green Bus Corridor in Dublin, which bans cars from the area, was introduced at 7am this morning.
Motorists were warned to expect delays in Dublin this evening as the ban came back into operation from 4pm to 7pm.
The new bus corridor will operate from Monday to Friday between 7am and 10am and 4pm and 7pm.
During these times only buses, taxis and cyclists will be allowed through College Green.
Private and commercial vehicles have been advised to use alternative routes.
Dublin City Council said the corridor aims to improve the flow of public transport through one of the city's major bottlenecks.
The U2 concert in Croke Park added considerably to traffic volumes tonight.
The Coach Tourism and Transport Council has welcomed the introduction of a bus gate.
CTTC Chief Executive CTTC Gerry Mullins said: 'The new system around College Green will be like the smoking ban: strange at first, but soon we'll wonder how we ever managed before it.
'The new system gives a further advantage to buses over cars, and this will encourage even more people to choose public transport.'
The CTTC represents over 60 private coach and bus operators in Ireland.
Elsewhere, a traffic management plan was put in place as the IKEA store beside the M50 in Ballymun opened this morning.