Kinds of roads and highways (in America)

There are about 3,900,000 miles (6,200,000 kilometers) of surfaced and unsurfaced streets, roads, and highways in the United States. Canada has about 550,000 miles (885,000 kilometers) of surfaced and unsurfaced roads.

Local and secondary roads make up about 80 per cent of the roads in the United States. Local roads carry traffic within a local area. Secondary roads link small communities and connect local roads to main highways leading to more distant places. Most local and secondary roads are built and maintained by local governments.

Primary highways. The most important roads generally are those that carry the greatest number of automobiles, trucks, and buses. These main roads, called primary highways, connect the larger communities. Most are constructed and cared for by state governments.

The federal government helps the states pay the cost of building and improving primary and secondary roads and streets. The routes are selected by states.

Some highways with four or more traffic lanes are divided in the center with a strip of land, called a median strip. This separates lanes of traffic going in opposite directions and helps prevent collisions.

Another important factor in safety and smooth traffic flow is the principle of controlled access. On fully controlled access highways a vehicle can enter or leave a main highway only at certain locations called interchanges. These interchanges are usually located at main crossroads. Grade separations are often used to separate crossing streams of traffic. In a grade separation one of the intersecting highways crosses over the other on a bridge. The two are connected by sloping, curved roadways called ramps.

With controlled access, no driveways from homes or commercial establishments connect directly with the main highway. Minor roads and streets run over or under the road without connecting to it. Minor roads may also dead-end at the highway or connect with a service road that runs parallel to the highway.

Freeways are main highways with full access control and grade-separated interchanges. Those with four or more lanes are divided by a median strip. Freeways in congested parts of big cities are often elevated (built above surface streets) or depressed (built below surface streets). The term freeway refers only to the free flow of traffic. Motorists may have to pay a toll to travel on these roads.

Expressways are similar to freeways but sometimes have only partial access control. Parkways are roads resembling freeways. But they are built in parklike surroundings with attractive landscaping and scenery. Most parkways are limited to passenger cars.

Bypasses are built to take motorists around cities. Motorists traveling some distance often do not want to drive through small towns or centers of large cities that lie on their routes. Those traveling from one part of a city to another also usually prefer to avoid downtown traffic. The bypass helps these motorists avoid city traffic, and reduces traffic congestion for those who want to drive into town.

Bypasses today are usually built as freeways, sometimes with service roads on one or both sides to serve local traffic.

Intersections are crossings of one road by another. Most intersections are at the same level, so that vehicles going east or west have to take turns crossing with vehicles going north and south. Sometimes roads intersect at odd angles and it is especially difficult to make a safe crossing. At such places the engineer may put islands in the paved area to keep traffic in the proper paths. When two freeways intersect, more complex interchanges are sometimes needed.