Historically many roads were simply recognizable routes without any formal construction or maintenance.

The Organisation for Economic Co-operation and Development (OECD) defines a road as "a line of communication (travelled way) using a stabilized base other than rails or air strips open to public traffic, primarily for the use of road motor vehicles running on their own wheels," which includes "bridges, tunnels, supporting structures, junctions, crossings, interchanges, and toll roads, but not cycle paths."

The Eurostat, ITF and UNECE Glossary for Transport Statistics Illustrated defines a road as a "Line of communication (travelled way) open to public traffic, primarily for the use of road motor vehicles, using a stabilized base other than rails or air strips. Included are paved roads and other roads with a stabilized base, e.g. gravel roads. Roads also cover streets, bridges, tunnels, supporting structures, junctions, crossings and interchanges. Toll roads are also included. Excluded are dedicated cycle lanes."

The 1968 Vienna Convention on Road Traffic defines a road as the entire surface of any way or street open to public traffic.

In urban areas roads may diverge through a city or village and be named as streets, serving a dual function as urban space easement and route. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel.

United Kingdom

In the United Kingdom The Highway Code details rules for "road users", but there is some ambiguity between the terms highway and road. For the purposes of the English law, Highways Act 1980, which covers England and Wales but not Scotland or Northern Ireland, road is "any length of highway or of any other road to which the public has access, and includes bridges over which a road passes." This includes footpaths, bridleways and cycle tracks, and also road and driveways on private land and many car parks. Vehicle Excise Duty, a road use tax, is payable on some vehicles used on the public road.

The definition of a road depends on the definition of a highway; there is no formal definition for a highway in the relevant Act. A 1984 ruling said "the land over which a public right of way exists is known as a highway; and although most highways have been made up into roads, and most easements of way exist over footpaths, the presence or absence of a made road has nothing to do with the distinction. Another legal view is that while a highway historically included footpaths, bridleways, driftways, etc., it can now be used to mean those ways that allow the movement of motor-vehicles, and the term rights of way can be used to cover the wider usage.

United States

In the United States, laws distinguish between public roads, which are open to public use, and private roads, which are privately controlled.

The assertion that the first pathways were the trails made by animals has not been universally accepted; in many cases animals do not follow constant paths. Others believe that some roads originated from following animal trails. The Icknield Way is given as an example of this type of road origination, where man and animal both selected the same natural line. By about 10,000 BC, rough roads/pathways were used by human travelers.

• The world's oldest known paved road was constructed in Egypt some time between 2600 and 2200 BC.
• Stone- paved streets are found in the city of Ur in the Middle East dating back to 4000 BC
• Corduroy roads (log roads) are found dating to 4000 BC in Glastonbury, England.
• The Sweet Track, a timber track causeway in England, is one of the oldest engineered roads discovered and the oldest timber trackway discovered in Northern Europe. Built in winter 3807 BC or spring 3806 BC, tree-ring dating (Dendrochronology) enabled very precise dating. It was claimed to be the oldest road in the world until the 2009 discovery of a 6,000-year-old trackway in Plumstead, London.
• Brick-paved streets were used in India as early as 3000 BC.
• In 500 BC, Darius I the Great started an extensive road system for the Achaemenid Empire (Persia), including the Royal Road, which was one of the finest highways of its time, connecting Sardis (the westernmost major city of the empire) to Susa. The road remained in use after Roman times. The easternmost destinations of these road systems were in Bactria and India.
• In ancient times, transport by river was far easier and faster than transport by road, especially considering the cost of road construction and the difference in carrying capacity between carts and river barges. A hybrid of road transport and ship transport beginning in about 1740 is the horse-drawn boat in which the horse follows a cleared path along the river bank.
• From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, in support of its military campaigns. At its peak the Roman Empire was connected by 29 major roads moving out from Rome and covering 78,000 kilometers or 52,964 Roman miles of paved roads.
• In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those in Baghdad, which were paved with tar. Tar was derived from petroleum, accessed from oil fields in the region, through the chemical process of destructive distillation.
• The Highways Act 1555 in Britain transferred responsibility for maintaining roads from government to local parishes. This resulted in a poor and variable state of roads. To remedy this, the first of the "Turnpike trusts" was established around 1706, to build good roads and collect tolls from passing vehicles. Eventually there were approximately 1,100 trusts in Britain and some 36,800 km (22,870 miles) of engineered roads. The Rebecca Riots in Carmarthenshire and Rhayader from 1839 to 1844 contributed to a Royal Commission that led to the demise of the system in 1844, which coincided with the development of the UK railway system.

Road design is part of highway engineering. Structural road design is designing a road for its environment in order to extend its longevity and reduce maintenance. The Shell pavement design method is used in many countries for the design of new asphalt roadsides.

Adverse camber

where a road slopes towards the outside of a bend, increasing the likelihood that vehicles travelling at speed will skid or topple. Usually only a temporary situation during road maintenance.

Alignment

the route of the road, defined as a series of horizontal tangents and curves.

All-weather road

Unpaved road that is constructed of a material that does not create mud during rainfall.

Banked turn

Bicycle boulevard

A street that allows local vehicle traffic, but is prioritized for bicycles and other non-motorized travel

Belisha Beacon

an orange globe, lit at night, used to highlight a pedestrian crossing

 

A beach road (Newcastle NSW Australia)

Bollard

Rigid posts that can be arranged in a line to close a road or path to vehicles above a certain width

Byway

Highway over which the public have a right to travel for vehicular and other kinds of traffic, but is used mainly as a footpath or bridleway

Bypass

Road that avoids or "bypasses" a built-up area, town, or village

Bottleneck

Section of a road with a carrying capacity substantially below that of other sections of the same road

Botts' dots

Non-reflective raised pavement marker used on roads

Camber (or crown)

the slope of the road surface downwards away from the centre of the road, so that surface water can flow freely to the edge of the carriageway, or on bends angling of the surface to lean traffic 'into the bend' reducing the chance of a skid.

Cant

Another name for cross slope or camber

Carriageway

Part of the road intended for the movement of road motor vehicles; the parts of the road which form a shoulder for the lower or upper layers of the road surface are not part of the roadway, nor are those parts of the road intended for the circulation of road vehicles which are not self-propelled or for the parking of vehicles.

Cat's eye

reflective raised pavement marker used on roads

Chicane

Sequence of tight serpentine curves (usually an S-shape curve or a bus stop)

Chipseal

Road surface composed of a thin layer of crushed stone 'chips' and asphalt emulsion. It seals the surface and protects it from weather, but provides no structural strength. It is cheaper than asphalt concrete or concrete. In the United States it is usually only used on low volume rural roads

Corniche

Road on the side of a cliff or mountain, with the ground rising on one side and falling away on the other

Cross slope

The slope of the pavement, expressed as units of rise per unit of run, or as a percentage

Curb (kerb)

A raised edge at the side of the roadway.

Curb extension

(also kerb extension, bulb-out, nib, elephant ear, curb bulge and blister) Traffic calming measure, intended to slow the speed of traffic and increase driver awareness, particularly in built-up and residential neighborhoods.

Cycle lane

Part of a carriageway designated for cycles and distinguished from the rest of the carriageway by longitudinal road markings. Mopeds may also be allowed to use a cycle lane.

Cycle track

Independent road or part of a road designated for cycles and sign-posted as such. A cycle track is separated from other roads or other parts of the same road by structural means. Mopeds may also be allowed to use the cycle track.

Cycling infrastructure

cycling-friendly infrastructure integrated into the roadway or in its own right of way

Drainage gradient

Farm-to-market road

a state road or county road that connects rural or agricultural areas to market towns.

Fork

(literally "fork in the road") Type of intersection where a road splits

Grade

Longitudinal