(NHS). Highway 28 from Highway 63 to Cold Lake is designated a NHS feeder route and Highway 58 between Rainbow Lake and Highway 88 is designated a NHS northern/remote route. Highways 1, 2, 3, 4, 16, and 43 are considered Alberta's most important interprovincial and international highways and are divided highways (expressways) or freeways for much or all of their length. Speed limits are generally divided highways/freeways and on others. Segments of Highway 1 and Highway 16 through the national parks within Alberta's Rockies that can be or . The Highway 15/28A/28/63 corridor between Edmonton and Fort McMurray is considered one of Alberta's most important intraprovincial highways. It is vital to the oilsands operation. Although only Highways 1, 2, 3, 4, 11, 15, 16, 43, 60, 63, 100, 201, and 216 are twinned (expressways) for most of their length, the vast majority of Alberta's 1 to 216 series of highways are two-laned and paved. Only four highways within the series have segments that remained gravelled. These include segments of Highways 40, 58, and 68 and a short segment near the northern terminus of Highway 63. Highways 1 and 16 are Trans-Canada Highway routes and are signed with TCH shields, not standard provincial shields. X series The roads in the X series are typically highways that are planned realignments or spurs of existing highways. The numbers applied to each highway in the X series are derived from the highway that is planned for realignment or spurred from (e.g. Highway 16X will be a realignment of Highway 16, and Highway 10X is spur from Highway 10). 500 - 986 series Alberta's 500 - 986 series of provincial highways are generally considered local or rural highways. The 500 - 986 series of provincial highways is divided into three sub-series: The 500/600 highways are west–east roads where the numbering increases northward from the Montana border to the Northwest Territories border. The 700/800 highways are south–north roads where numbering increases eastward from the British Columbia border to the Saskatchewan border. The 900 highways are newer or planned roads that have been established for future consideration as or as potential extensions or realignments of highways within the 1 - 216 series. Some of these highways are paved, while others are entirely or partially gravel. Rural speed limits range from to . 500 600 700 800 900 The roads in the 900 are typically highways that are