There are often restrictions to what one-way streets are good candidates for allowing two-way cycling traffic. In Belgium road authorities can in principle allow any one-way streets in 50 kilometres per hour (31 mph) zones to be two-way for cyclists if the available lane is at least 3 metres (9.8 ft) wide (area free from parking) and no specific local circumstances prevent it.[51] Denmark, a country with high cycling levels, does not use one-way systems to improve traffic flow.[52] Some commentators argue that the initial goal should be to dismantle large one-way street systems as a traffic calming/traffic reduction measure, followed by the provision of two-way cyclist access on any one-way streets that remain.[53]