Authors: Dr. Jean-Paul Rodrigue and Dr. Brian Slack

Road transportation involves moving passengers and freight with vehicles over a prepared surface.

1. The Setting of Road Transport Systems

Roads and rails are the two major modes that compose the land transport system. Roads were established first, as steam rail technology only became available by the 18th century, amid the industrial revolution. Historical considerations are important in assessing the structure of current land transportation networks. Modern roads tend to follow the network structure established by previous roads, as was the case for the contemporary European road network. The current roads of Italy, France, and Britain follow the structure established by the Roman road network centuries before. Therefore there is a strong path dependency effect of road transport networks.

The first land roads took their origins from trails, which were generally used to move from one hunting territory to another through seasonal migrations. With the emergence of the first empires, trails started to be used for commercial purposes as trade expanded, collecting taxes, and moving military forces. Some became roads, primarily by domesticating horses, mules, and camels. The use of wheeled vehicles encouraged the construction of better roads to support the additional weight since heavier vehicles quickly damage an unpaved surface. Further, persistent rainfall could damage and make unpaved roads impractical, particularly if there was a rainy season. A road transport system requires a level of labor organization, financing, and administrative control that could only be provided by a form of governmental oversight, offering some military protection over trade routes and being able to provide maintenance work. It was not uncommon that communities along road systems were required to provide free road construction and maintenance work as part of their feudal obligations.

By 3,000 BCE, the first paved roads appeared in Mesopotamia, and asphalt was used as pavement in Babylon by 625 BCE. The Persian Empire had a road system of 2,300 km in the 5th century BCE, the first functional road system in history. However, the Roman Empire established the first major road system from 300 BCE onward, mainly for economic, military, and administrative reasons. It relied on reliable road engineering methods, including the laying of foundations and the construction of bridges. This was also linked with establishing pan-continental trading routes, such as the Silk Road, linking Europe and Asia by 100 BC. However, most of these routes were marked paths along steppes and other semi-arid areas.

Following the fall of the Roman Empire in the 5th century, integrated road transportation collapsed in Europe as most roads were locally constructed and maintained. Because of the lack of maintenance of many road segments and fragmented political entities, land transport became a hazardous activity-still, empires such as the Byzantine Empire maintained road networks. From the 14th century, the Incas built an extensive road system in the Andes, which may have spanned more than 40,000 km. However, the system was only used by foot and pack animals (Llamas).

The creation of modern nation-states in the 17th century allowed national road transportation systems to be formally established. In the 18th century France, through central government efforts, built a Royal Roads system spanning 24,000 km, over which a public transport service of stagecoaches carrying passengers and mail was established. The British, mainly through private efforts, built a 32,000 km system of turnpikes where tolls had to be paid for road usage. A similar initiative was undertaken in the United States in the 19th century, and by the early 20th century, a network of 3 million km of roads, most unpaved, was in operation. 1794 marks the beginning of modern road transportation with the first mail coach service between London and Bristol, operating under a timetable.

Also of high significance were technological innovations in road engineering that permitted the construction of reliable and low-cost hard surface roads. One such achievement came from the Scottish engineer McAdam who developed a process (later known as macadam) where hard and waterproof road surfaces were made by cemented crushed stone, bound together either with water or bitumen. It provided a cheaper, durable, smooth, and non-slippery pavement, considerably improving the reliability and travel speed on roads. Many roads could now be used reliably year-round. Road development accelerated in the first half of the 20th century. By the 1920s, the first all-weather transcontinental highway, the Lincoln Highway, spanned over 5,300 km between New York and San Francisco. However, it was merely a set of connected roads with inconsistent design and maintenance. Germany was the first to build a modern highway (autobahn) in 1932, with specifications such as restricted access, overpasses, and road separation that would eventually become common characteristics of contemporary highway systems.

The post-World War II era represented a period of rapid expansion of road transportation networks worldwide. The most remarkable road transport engineering achievement of this era was the setting of the American Interstate highway system. Its construction began in 1956 with the strategic purpose of providing a national road system servicing the American economy and also being able to support troop movements and act as airstrips in case of an emergency (although the latter two purposes were never used). About 56,000 km were built between the 1950s and the 1970s, marking the years of its fastest expansion. Between 1975 and 2006, only 15,000 km was added to the system, underlining growing construction costs and diminishing returns. Overall, about 70,000 km of four-lane and six-lane highways were constructed, linking all major American cities, coast to coast. A similar project occurred in Canada, with the Trans-Canada highway completed in 1962. Other developed economies quickly followed.

By the 1970s, every modern nation had constructed a national highway system, which resulted in a pan-European system, in the case of Western Europe. This trend now takes place in many developing economies as one of the first signs of economic development is an accelerated process of road construction. For instance, China is building a national highway system that expanded to 169,000 km in 2021, largely surpassing the length of the American Interstate. Another notable recent example concerns the Indian national highway system, dubbed the Golden Quadrilateral, due to its rectangular shape connecting India’s most important cities (Delhi, Kolkata, Chennai, and Mumbai). Construction of the 5,800 km highway system began in 2001 and was completed in 2013. Highway construction projects have become common in developing economies, such as in Latin America and Subsaharan Africa, underlining the rapid pace of motorization once intermediate income levels are reached.

2. The Spatial Impacts of Road Transportation

Road transportation is the mode that has expanded the most over the last 50 years, both for passengers and freight markets. This represents a dramatic change in the built environment with the massive addition of road infrastructures supporting urban mobility and connecting cities. The footprint of road transportation is extensive, but its scope remains local and regional, more so for passengers than for freight. For passengers, the growth of road usage has mainly been fueled by rising incomes with their impacts on car ownership and suburbanization. Growth in road freight transport has been fueled mainly by rising income and consumption levels and globalization. The load capacity of vehicles has improved, and vehicles have been adapted to freight market segments such as perishables, fuel, construction materials, and containers. An array of problems, such as fuel consumption, environmental externalities, traffic congestion, and safety (accidents), have also emerged.

Roads have a functional hierarchy depending on their role in the transport network. At the top of the hierarchy are freeways (highways), which are limited-access roads with no intersections. To connect intersecting highways, a large number of interchanges were built, leading to a variety of designs to mitigate traffic flow and the required footprint. The cloverleaf interchange has become one of the most common. There are also arterials, roads with traffic signals at intersections, forcing vehicles to stop. These arterials are fed by collectors and local roads, which mainly connect specific activities (residences, retail stores, industries). This network enables point-to-point services, a notable advantage road transport has over other modes.

Road transport modes have limited potential to achieve economies of scale. This is due to the size and weight constraints imposed by regulations and the technical and economic limits of engines. In most jurisdictions, trucks, and buses have specific weight and length restrictions, which are imposed for safety reasons, but also because intensive road use by heavy trucks damage road infrastructure and increases maintenance costs. While in the United States, the maximum gross vehicle weight is 36 metric tons (80,000 pounds), in Europe and China, these figures are 40 (88,000 pounds) and 49 (100,000 pounds) metric tons, respectively. In addition, there are severe limits on the traction capacities of cars, buses, and trucks because of the considerable growth in energy consumption that accompanies increases in vehicle weight. For these reasons, the carrying capacities of individual road vehicles are limited, and there is limited technological potential to improve them.

Road transportation is characterized by an acute traffic concentration along a Pareto distribution; commonly, 20% of the road network supports 60 to 80% of the traffic. This observation is expanded by the fact that societies have important differences in terms of the density, capacity, and quality of their road transport infrastructures, mainly due to their level of development. Acute geographical variations of the assets and inventory are the norm. The technological evolution of road transport vehicles has been a continuous trend since the first automobiles were built. However, the underlying motive technology is very similar, as road transportation massively relies on the internal combustion engine.

New materials (ceramic, plastic, aluminum, composite materials), fuels (electricity, hydrogen, natural gas), and information technologies (vehicle control, diagnostic, location, navigation, and toll collection) are continuously integrated into road vehicles to improve their efficiency and reliability. However, there are signs that peak mobility, as measured in vehicle-miles traveled, can be achieved for road transportation when car use has reached an optimum diffusion level. Countervailing forces are at play, such as congestion, the aging of the population, and even information technologies (teleworking). For trucking, demand continues to grow, driven by rising incomes, global supply chains, and e-commerce.

The urban population has increased considerably over the last 50 years, and about 56% of the global population was urbanized as of 2020. It is challenging for developing economies to have rates of individual vehicle ownership similar to those of advanced economies, especially compared to the United States. The primary constraint is not the lack of income, but the physical lack of space to accommodate a high level of car ownership. This will impose new or alternative methods to transport freight and passengers over urban roads. Reducing vehicle emissions and the impacts of infrastructures on the environment are mandatory to promote a sustainable environment. Under such circumstances, micromobility, particularly cycling, is thus considered an alternative to the automobile in urban areas, widely adopted in developing economies, although more for economic reasons. However, the potential of micromobility is related to its substitution for existing public transit users. There is limited potential to substitute car trips with bicycle trips since most car trips cover longer distances that are not easily substituted by other modes, including the bicycle. Bicycle parking schemes at urban transit stations are a strategy that can be used to incite a substitution. Bicycle pools have also been created to incite urban residents to use them for short trips, including e-scooters made available for rent on sidewalks.

Even with the presence of alternatives, road transport retains significant advantages over other modes:

• The capital cost of vehicles is relatively low, making it comparatively easy for new users to gain entry. This helps ensure that the trucking industry, for example, is highly competitive, but with low-profit margins. Low capital costs ensure that innovations and new technologies can diffuse quickly through the industry since a fleet can be renewed over a decade.
• Road vehicles have a high relative speed compared with non-motorized forms of transportation and public transit, the major constraint being regulatory speed limits.
• Road transportation offers the flexibility of route choice, once a network of roads is provided. It has the unique opportunity to provide door-to-door services for passengers and freight.

These multiple advantages have made cars, buses, and trucks the modes of choice for many trip purposes, leading to their market dominance for short-distance trips. The success of cars and trucks has given rise to several serious problems. Road congestion has become a feature of most urban areas around the world. In addition, road transport is behind many major environmental externalities linked to transportation, particularly CO2 emissions. Addressing these issues is becoming a significant policy challenge. A symbiosis between types of roads and types of traffic with specialization (reserved lanes and hours) is to be expected.

An enduring challenge for road freight transportation concerns empty backhauls. Due to trade and commercial flow imbalances, about 20% of all truck flows are empty. This characteristic is complex to mitigate since it is related to the fundamental structure of freight demand. For instance, all retail-related freight flows are usually in one direction, such as from the manufacturing plant to the distribution center and from the distribution center to the store or the consumer’s home for e-commerce. There are limited opportunities for return cargo for these flows.

3. Infrastructures and Investments

Road infrastructures are moderately expensive to provide, but there is a wide divergence of costs, from a gravel road to a multi-lane urban elevated expressway. Because road vehicles can climb moderate slopes, physical obstacles are less important than other land modes. Most roads are provided as a public good by governments, while most vehicles are privately owned. Capital costs, therefore, are generally assumed by society and do not fall as heavily on one source, as is the case for other modes. Unlike many transport infrastructures where the user pays for the network through pricing mechanisms, the public sector covers 95% of road infrastructure financing, leaving the remainder covered by tolls. Road transportation thus has a unique characteristic where several costs are externalized, which is an indirect form of mobility subsidy.

The public offering of free road infrastructure conveys several advantages to the private sector but can also lead to externalities. The main advantage is clear; road users commonly do not bear the full operating costs implying that road transportation tends to be below the real market price. This can be seen as a subsidy for road freight transportation, as road maintenance is not part of the operating costs but is indirectly present with taxes and tolls. As long as there is spare road capacity, this situation works for the benefit of the users. However, when congestion arises, users have limited influence on constructing new and improved infrastructure to mitigate the problem since they do not own the infrastructure and are using it free of charge.

Lobbying public entities to receive public road infrastructure investments can be a very long process, subject to constant delays and changes. Road users thus become trapped in a situation they can do little to change since it is provided free of charge. This can be labeled as the “free roads curse“. An entity owning and operating its own network, such as a rail company in North America, has the advantage of directly implementing improvements with its capital if congestion arises on a segment of its network. It is thus better placed to cope with congestion and respond with strategic investments less subject to political capture.

Governments can expropriate the necessary land for road rights of way since a private enterprise may have difficulties expropriating without government support. Another important aspect of roads is their economies of scale and their indivisibility, underlining that the construction and maintenance of roads are cheaper when the system is extensive but to a limit. Paradoxically, all road transport modes have limited abilities to achieve scale economies. This is due to the size constraints imposed by governments, the technical and economic limits of the power sources, and what infrastructures can bear weight-wise. In most jurisdictions, trucks and buses have specific weight and length restrictions. Thus, there are system-wide benefits to expanding road networks but vehicle-wise limits. In addition, there are severe limits on the traction capacities of road vehicles because of the considerable increases in energy consumption accompanying increases in the weight of the transported unit. For these reasons, the carrying capacities of individual road vehicles are limited. Even if roads are costly infrastructures to build and maintain, they are also sources of revenue:

• Costs. They include the costs to secure rights of way, including expropriation costs, which can be prone to delays. Development costs (planning), construction, maintenance, and administration costs are significant. The construction costs of a simple two-lane road can reach 2 to 3 million dollars per kilometer in a low-density area, which can easily double for higher-density areas. There are opportunity costs to road construction in the form of losses in land taxes and external costs related to accidents and pollution.
• Revenue. Road transportation is associated with multiple sources of public revenue, including registration, gas taxes, sales taxes for the purchases of vehicles, tolls, parking, and insurance fees. Indirectly, road transportation creates demand for the manufacturing of vehicles, repair and maintenance services, and energy provision and distribution. Another form of indirect income concerns traffic violations (e.g. speeding) that use the rationale of public safety to hide revenue-generation practices by local governments.

In many cases, governments have been challenged as custodians of road infrastructure. Delaying road maintenance or improvements is tempting because of the high costs involved. Budgetary constraints are also inciting increasing taxes and tolls, selling assets, and reducing expenses. Consequently, a growing number of roads have been privatized, and companies specializing in road management have emerged across the world. For existing roads, privatization is only possible on specific trunks that have important and stable traffic. For new roads, levying tolls is a strategy to recover investments and attract private investors. Private enterprises usually have a vested interest in seeing that the road segments they manage are maintained and improved since the quality of the road will be directly linked to revenue generation. Most toll roads are highways linking large cities or bridges and tunnels where there is a convergence of traffic. Despite privatization attempts, most roads are not economically profitable but must be socially present as they are essential to service populations. It can thus be expected that roads will remain dominantly publicly funded in the future and a recurring construction and maintenance challenge.

---

Related Topics

• 5.1 – Transportation Modes, Modal Competition and Modal Shift
• 8.3 – Urban Mobility
• 8.4 – Urban Transport Challenges

Bibliography

• International Transportation Forum (2021), Road Safety Annual Report 2021, OECD Publications, Paris.
• Lay, M.G. (1992) Ways of the World: A History of the World’s Roads and of the Vehicles that Used Them. New Brunswick, New Jersey: Rutgers University Press.
• Lay, M., J. Metcalf and K. Sharp (2020) Paving Our Ways: A History of the World’s Roads and Pavements, New York: CRC Press.
• Lewis, T. (2013) Divided Highways: Building the Interstate Highways, Transforming American Life. Ithaca, NY: Cornell University Press.
• Meijer, J.R., Huijbregts, M.A.J., Schotten, C.G.J. and Schipper, A.M. (2018) “Global patterns of current and future road infrastructure”. Environmental Research Letters, 13-064006. Data is available at www.globio.info
• World Health Organization (2018) Global status report on road safety 2018. Geneva: World Health Organization; 2018. Licence: CC BYNC-SA 3.0 IGO.