Two-lane highways constitute the vast majority of roadways by length, particularly in rural areas. This is true here in the USA and in most other countries around the world. It is these highways that first brought motor vehicles to remote towns and villages over the past century and played a critical role in the growth and economies of rural communities. The dominance of two-lane highways in the current roadway networks in developed countries is driven by economics and the low level of vehicular traffic common in rural areas.

Two-lane highways serve various highway functions, from local roads serving very low volumes of local traffic to principal arteries connecting towns and small cities, and everything in between. Consequently, these highways vary in their standards, from unpaved highways in very remote areas to high-type pavement and wider cross sections for intercity routes and major arteries.

Two-lane highways, as we know them today, were mainly introduced with the introduction of the automobile. With the increase in motor vehicle traffic and the use of larger vehicles including buses and trucks, the majority of two-lane highways outside remote and frontier rural areas were paved to sustain traffic loads.