As of the January 20, 2005, the measurement of speed limits on the Republic of Ireland (ROI) roads changed from miles per hour (mph) to kilometers per hour (km/h). There has also been significant changes to speed limits on certain roads in the ROI along with some new vehicle speed limits.

Motorists are urged to remember the change of driving laws when crossing the border. New signs in the ROI display the new speed limits in kilometers per hour. However, motorists should also be aware that on some roads permitted speeds are now different to those in Northern Ireland.