In Finland, highways are separated into three categories: all-access "valtatie" ("main road"), limited-access "moottoriliikennetie" ("motor traffic road") and finally "moottoritie" ("motorway"); the latter two are marked with green signage, while "valtatie" signage is blue. While most of the network is all-access road, of it is motorway, and is limited-access road. The access is limited to motor vehicles faster than 50 km/h, thus excluding pedestrian, bicycle, moped or tractor traffic; furthermore, towing is not allowed. Limited-access roads are generally similar to motorways, but do not fulfill all the technical requirements, such as several lanes in one direction or separation of opposite directions. Limited-access roads are usually built because the local population density is too low to justify a motorway. Often space has been left during construction for an eventual upgrade to a motorway. Limited-access roads also function as feeder routes for motorways. The general speed limit on main roads and limited-access roads is 100 km/h (summertime) and 80 km/h (wintertime). On motorways the speed limits are 120 and 100 km/h respectively. Especially during winter the speed limits can be changed due to weather conditions.