Road construction in Yellowknife is often a challenge due to the presence of permafrost which requires that roads generally be regraded and resurfaced every 10 to 20 years. Most roads in Yellowknife are paved and road width varies from . Winter snow removal is done on a regular schedule by the City of Yellowknife public works department. Speed limits are on most roads, in school zones, and on highways. School zones and playground zones are in effect 24 hours per day 7 days per week. The highway system in the NWT is maintained by the Government of the Northwest Territories. Highway 4 (Ingraham Trail) and Highway 3 (Yellowknife Highway) both run through Yellowknife and are all-weather roads. One well-known, almost infamous, road in Yellowknife is Ragged Ass Road, after which Tom Cochrane named an album.