European route E4 passes from north to south through Sweden from the border with Finland, with a total length of 1,590 kilometres (990 mi). The Finnish part lies entirely within Tornio in northern Finland, and is only 1 kilometre (0.62 mi) long. The Swedish part traverses most of Sweden except the extreme north and the west coast region, and is commonly considered the highway backbone of Sweden, since it passes in the vicinity of many of its largest cities and through the capital Stockholm. In particular, it is the mainline road used by most vehicle traffic, both cars and lorries, between the north (Norrland) and south of Sweden or beyond.

Tornio is a city and municipality in Lapland, Finland. The city forms a cross-border twin city together with Haparanda on the Swedish side. The municipality covers an area of 1,348.83 square kilometres (520.79 sq mi), of which 161.59 km2 (62.39 sq mi) is water. The population density is 17.68 inhabitants per square kilometre (45.8/sq mi), with a total population of 21,018.