Roman roads fell into disrepair in medieval Europe due to a lack of resources and knowledge to maintain them, but many continued to be used. The alignments are still partially used today, such as on parts of England's Route A1. Before the 19th century, there were no organized networks of streets within cities, and only passing paths. With the invention of the harness "Harness (garrison)" and cars with pivoting front axles, which allowed making tight curves, street networks in cities were established.[15]​.

In medieval Islam, numerous roads were built in the Arab Empire. The most sophisticated were those of Baghdad, in Iraq, paved with tar in the 19th century. The tar was obtained from oil from the existing springs in the region, through distillation.[16]​.

A medida que los estados de Europa se desarrollaban y enriquecían, especialmente durante el Renacimiento, comenzaron a construirse nuevas carreteras y puentes, a menudo basados en los diseños romanos. Aunque se produjeron intentos de redescubrir los métodos romanos, hubo poca innovación útil en la construcción de carreteras antes del siglo .

En el siglo , el transporte por carretera en el Imperio asante (en el África Occidental) se mantenía a través de una red de caminos bien mantenida que conectaba la capital del imperio con los territorios bajo su jurisdicción e influencia.[17]​[18]​ Tras la importante construcción de carreteras realizada en el Reino de Dahomey, se estableció un sistema de peaje, con la función de recaudar impuestos anuales basados en las mercancías transportadas por el Camino Real,[19]​ que fue construido a finales del siglo por el rey Kpengla, extendiéndose desde Abomey hasta Ouidah pasando por Cana.[20]​.

Entre 1725 y 1737, el general George Wade construyó una carretera de 250 millas (402,3 km) que contaba con 40 puentes, para mejorar el control de Gran Bretaña sobre las Tierras Altas de Escocia, utilizando diseños de calzadas romanas con grandes piedras en la base y grava en la parte superior, con una profundidad total de dos metros. La calzada estaba tan mal alineada y era tan empinada, según Thomas Telford, «que era inadecuada para la vida civil», además de ser irregular y con mal drenaje.[21]​.

Toll roads

In England, responsibility for the condition of roads lay with each local parish since Tudor times. In 1656, the parish of Radwell (Hertfordshire) petitioned Parliament for help in maintaining its section of the Great Northern Road.[22] Parliament passed an act giving local magistrates the power to erect tolls on a section of the Great Northern Road, between Wadesmill (Hertfordshire); Caxton (Cambridgeshire) "Caxton (Cambridgeshire)"); and Stilton "Stilton (Cambridgeshire)") (Huntingdonshire), for a period of eleven years. The revenue thus raised would be used to maintain the Great Northern Highway in their jurisdictions.[22][23] The toll erected at Wadesmill became the first effective toll in England.

El primer sistema con fideicomisarios que no eran jueces se estableció mediante una ley de peajes en 1707, para un tramo de la carretera Londres-Chester entre Fornhill y Stony Stratford. El principio básico era que los fideicomisarios gestionarían los recursos de las diversas parroquias por las que pasaba la carretera, los complementarían con los peajes de los usuarios de fuera de las parroquias y destinarían la totalidad al mantenimiento de la carretera principal. Esto se convirtió en el modelo para la construcción de peajes en un número creciente de carreteras, solicitado por quienes deseaban mejorar el flujo comercial a través de su parte del condado.[22]​.

At the turn of the century, sections of major radial roads leading to London were placed under the control of individual toll road trusts. The pace of creation of new toll roads accelerated in the 1750s, with the creation of trusts to maintain the transverse routes between the Great Highways radiating from London. Roads leading to some provincial towns, especially in the west of England, were placed under individual trusts, and key roads in Wales became toll roads. In South Wales, the roads of entire counties were placed under individual trusts in the 1760s. A new surge in trust formation took place in the 1770s, with the introduction of tolls for subsidiary connecting roads, routes over new bridges, new routes in growing industrial areas and highways in Scotland. By 1750 some 150 trusts had been established; By 1772, another 400 had been established, and by 1800, there were more than 700.[24] By 1825, some 1,000 organizations controlled 18,000 miles (28,968.1 km) of roads in England and Wales.[25]

The laws of these new trusts and the renewal laws of the previous ones incorporated a growing list of powers and responsibilities. Beginning in the 1750s, laws required trusts to construct milestones indicating the route and distance in miles between major towns on the road. Users were required to follow traffic rules, such as driving on the left, and not to damage the road surface. Trusts could charge additional tolls during the summer to pay for road irrigation needed to reduce dust raised by vehicles. Parliament also passed some general toll road laws addressing trust administration and restrictions on wheel width, as narrow wheels caused considerable damage to the road.

The quality of early toll roads varied.[26] While their construction involved some improvement to each road, the technologies used to address geological features, drainage, and the effects of climate were in their early stages. Road construction improved slowly, initially through the individual efforts of some engineers such as John Metcalf&action=edit&redlink=1 "John Metcalf (engineer) (not yet drafted)") in Yorkshire in the 1760s. British toll road builders[27]​ began to understand the importance of selecting clean stones for paving and excluding plant material and clay to achieve smoother roads. durable.[21][28]​.

Highways built in the United States used to be built by private companies under a government franchise. They tended to parallel or replace existing routes with a certain volume of trade, with the hope that the improved road would divert enough traffic to make the investment made profitable. Plank-paved roads were particularly attractive, as they greatly reduced rolling resistance and mitigated the problem of waterlogging. Better grading to soften the slope of the most difficult sections allowed draft animals to carry heavier loads.

Metcalf

The first professional road builder to emerge during the Industrial Revolution was John Metcalf&action=edit&redlink=1 "John Metcalf (engineer) (not yet drafted)"), who built approximately 180 miles (289.7 km) of toll roads, mainly in the north of England, beginning in 1765, when Parliament passed an act authorizing the creation of toll trusts to build toll-financed roads in the area of Knaresborough. Metcalf was awarded a contract to build a three-mile (5 km) stretch of road between Minskip and Ferrensby, as part of a new road that would connect Harrogate and Boroughbridge. He explored the rural area alone and calculated the most practical route.

He believed that a good road should have good foundations, good drainage, and a smooth convex surface to allow rainwater to drain quickly into the side ditches. He understood the importance of good drainage, knowing that rainfall was the cause of most road problems. He found a way to build a road through a bog using fajinas, tied bundles of calluna (a type of heather) and gorse branches as foundations. This cemented his reputation as a road builder, as other engineers believed it was impossible. He mastered his craft with his own method of calculating costs and materials, which other engineers did not understand.

Trésaguet

Pierre-Marie-Jérôme Trésaguet") is widely credited with establishing the first scientific method for road construction in France. In 1775, he wrote a memorandum on his method, which became general practice in his country. It consisted of a layer of large rocks covered by a smaller layer of gravel. The bottom layer improved on Roman practice, as it was based on the idea that the purpose of this layer (the subbase) is to transfer the weight of the road and from traffic to the ground, while protecting it from deformation by distributing the weight evenly. Therefore, the subbase did not have to be a self-supporting structure. The upper running surface provided a smooth surface for the vehicles, while protecting the large stones of the subbase.

Trésaguet understood the importance of drainage through the construction of deep lateral ditches, but he also insisted that his roads be accessible from the sides, which prevented the provision of the aforementioned ditches. Well-maintained surfaces and drains protect the integrity of the subbase, and Trésaguet introduced a continuous maintenance system, whereby each road worker was assigned a section of road to keep in optimal condition.[29]​.

Telford

The surveyor and engineer Thomas Telford made substantial advances in the engineering of new roads and the construction of bridges. Its construction method consisted of excavating a large trench, on which a solid rock foundation sat. He designed his roads with a downward slope from the center (crown slope or camber), which allowed drainage of the road surface layers, an important improvement over Trésaguet's work. The surface consisted of crushed stone. He improved road construction methods by optimizing stone selection based on thickness, taking traffic, alignment and slopes into account. During his final years, Telford was responsible for the reconstruction of sections of the London to Holyhead road, a task completed by his assistant of ten years, John MacNeill.

His engineering work in the 1820s on the Holyhead road (precedent of the A5 motorway), reduced the travel time of the "Stagecoach (coach)") from 45 hours to just 27 hours, and the best speeds of the mail carriages increased from 5-6 mph (8-10 km/h) to 9-10 mph (14-16 km/h). Between London and Shrewsbury, most of his road work consisted of improvements. Beyond Shrewsbury, and especially after Llangollen, the work often involved building a toll road from scratch. Notable features of this section of the route include the Waterloo Bridge across the River Conwy at Betws-y-Coed, the ascent from there to Capel Curig, and then the descent from the Nant Ffrancon Pass towards Bangor ("Bangor (Wales)"). Between Capel Curig and Bethesda "Bethesda (Gwynedd)"), in the Ogwen Valley, Telford deviated from the original road, built by the Romans during their occupation of this area.[30]​.

McAdam

It would be another Scottish engineer, John Loudon McAdam, who designed the first modern roads. He developed an inexpensive paving material based on an aggregate of crushed stone and earth (known as macadam). His method of road construction was simpler than Telford's, and also more effective in protecting the tracks: he discovered that massive foundations of successive layers of rock were unnecessary, and claimed that the natural soil alone would support the road and traffic, provided it was covered by a crust that protected the underlying soil from water and wear.[31]

Unlike Telford and other road builders, McAdam laid out his roads as level as he could. Its 30-foot (9.1 m) wide road only required a 3-inch (7.6 cm) lift from the edges to the center. The banking and elevation of the road above the water table allowed rainwater to drain into the ditches on both sides.[33]​.

The size of the stones was fundamental to McAdam's theory of road construction. At the lower road thickness of 200 millimeters (7.9 in), the size of the stones was limited to less than 75 millimeters (3 in). The top layer of 50 millimeters (2 in) thick stones was limited to a size of 20 millimeters (0.8 in), and the stones were checked by supervisors with scales. A worker could quickly check the minimum allowable size of the stone for himself, seeing if it would fit in his mouth. The importance of the 20 mm size of the road course was that these stones had to be much smaller than the 100 mm wide iron wheels of the carriages that circulated on the road.

McAdam believed that the "proper method" of breaking stones, for convenience and speed, was for people to sit and use small hammers, breaking the stones so that none weighed more than six ounces. He wrote that the quality of the road would depend on the care with which the stones were spread over the surface over a considerable space, shovel by shovel.[34]​.

He also indicated that no substance that would absorb water should be incorporated, as it could affect the path in case of frost, nor should anything be placed on the clean stone to consolidate it. The action of road traffic caused the broken stone to combine with its own angles, forming a solid, level surface that would resist weather and traffic.[35] From his experience in road construction, McAdam had learned that a layer of broken cornerstones would act as a solid mass and would not require the large layer of stone previously used to build roads. By keeping stones smaller than the width of the wheel on the surface, a good rolling surface for traffic could be created. The small surface stones also provided little stress on the road, provided they were kept reasonably dry.[36]​ In practice, their roads proved to be twice as strong as those at Telford.[37]​.

Although McAdam had been adamantly opposed to filling the gaps between his small cut stones with smaller material, in practice road builders began to introduce filler materials, such as smaller stones, sand or clay, and it was noted that these roads were stronger as a result. "Macadam" roads were widely built in the United States and Australia in the 1820s and in Europe in the 1830s and 1840s.[38] These roads were suitable for use by horses and carriages or stagecoaches, but were very dusty and prone to erosion in heavy rain.

El Good Roads Movement fue un movimiento que se desarrolló en los Estados Unidos entre finales de la década de 1870 y la de 1920. Los defensores de la mejora de las carreteras, liderados por los ciclistas asociados a la Liga Americana, transformaron la agitación local en un movimiento político nacional. Fuera de las ciudades, las carreteras eran de tierra o de grava, con barro en invierno y polvo en verano. Los primeros organizadores tomaron como ejemplo el caso de Europa, donde la construcción y el mantenimiento de carreteras contaban con el apoyo de numerosos gobiernos nacionales y locales. En sus inicios, el objetivo principal del movimiento era promover la construcción de carreteras en las zonas agrícolas situadas entre las ciudades, y ayudar a las poblaciones rurales a obtener los beneficios sociales y económicos que se disfrutaban en las ciudades, donde los residentes se beneficiaban de ferrocarriles, tranvías y calles pavimentadas. Incluso más que los vehículos tradicionales, las bicicletas, recién inventadas, podían beneficiarse de las buenas carreteras rurales.

Más adelante, se vio que las carreteras de macadán no resistían el paso de vehículos cada vez más rápidos y pesados. Los métodos para estabilizar carreteras con brea se remontan al menos a 1834, cuando John Henry Cassell, al frente de la compañía "Cassell's Patent Lava Stone Works" del barrio londinenese de Millwall, patentó el "Pitch Macadam".[39]​ Este método consistía en extender alquitrán sobre una subbase granular, colocar encima una capa típica de macadán y, finalmente, sellarlo con una mezcla de alquitrán y arena. El macadán con lechada de alquitrán se utilizaba mucho antes de 1900 e implicaba escarificar la superficie de un pavimento de macadán existente, extender el alquitrán y volver a compactarlo. Aunque el uso del alquitrán en la construcción de carreteras ya se conocía en el siglo , se utilizaba poco y no se introdujo a gran escala hasta la llegada del automóvil a principios del siglo .

El tarmacadam o macadán asfáltico moderno fue patentado por el ingeniero civil británico Edgar Purnell Hooley"), quien observó que el alquitrán vertido sobre una calzada de macadán retenía el polvo y creaba una superficie lisa.[40]​ En 1901, obtuvo una patente para el procedimiento de asfaltado.[41]​ La patente de Hooley de 1901 implicaba la mezcla mecánica de alquitrán y áridos antes de su colocación y la posterior compactación de la mezcla con una apisonadora de vapor. El alquitrán se modificaba añadiendo pequeñas cantidades de cemento Portland, resina y/o brea.[42]​.

Controlled access highways

The first version of modern highways was developed during the first half of the century. The Long Island Motor Parkway in Long Island, New York "New York (state)"), opened in 1908 as a private initiative, was the world's first limited access highway. It included numerous modern features, such as banked curves, safety barriers, and asphalt concrete pavement.[45] Traffic could turn left between the main roadway and off-ramps, crossing oncoming traffic, so it was not a controlled-access highway (or a "expressway" proper, as later defined by the United States federal government's "Manual on Uniform Traffic Control Devices").

Modern controlled-access highways emerged in the early 1920s in response to rapidly increasing automobile use, growing demand for faster transportation between cities, and improvements in paving processes, techniques, and materials. These original high-speed roads, known as expressways, have been modernized and are still in use.

Italy was the first country in the world to build controlled access highways reserved for fast traffic, and only for motor vehicles.[43]​[44]​ The Autostrada A8 ("Lake Highway"), the first highway built in the world, connected Milan with Lake Como and Lake Maggiore, and was later integrated into the A8 and A9 motorways. It was designed by Piero Puricelli and opened in 1924.[44] This highway, originally called *autostrada"), contained only one lane in each direction and lacked interchanges. The Bronx River Parkway was the first highway in North America to use a strip in the median to separate opposing lanes. It was built through a park, and the streets that crossed it were crossed by bridges.[46][47]​ The Southern State Parkway opened in 1927, while the Long Island Motor Parkway closed in 1937 and was replaced by the Northern State Parkway (opened in 1931) and the adjacent Grand Central Parkway (opened in 1936). In Germany, construction of the Bonn-Cologne Autobahn began in 1929 and was opened in 1932 by Konrad. Adenauer, then mayor of Cologne "Cologne (Germany)").[48]​.

In Canada, the first pioneer highway with semi-controlled access was The Middle Road between Hamilton "Hamilton (Ontario)") and Toronto, which featured a median divider between opposing traffic flows, as well as the country's first cloverleaf interchange. This highway became the Queen Elizabeth Way, which had a cloverleaf and a trumpet interchange when it opened in 1937 and, until the Second World War, had the longest illuminated stretch of highway ever built.[49] A decade later, the first section of Ontario's Highway 401, based on earlier designs, opened. Since then, it has become the busiest highway in North America.

The term freeway was first used in February 1930 by Edward M. Bassett,[50]​[51][52]​ who argued that roads should be classified into three basic types: highways, avenues, and roads.[52]​ In Bassett's system, based on zoning and property rights, the owners of adjoining properties had the right to continue receiving sunlight, dominion over the vertical flight of their plots and access to the road; but not from avenues or highways. These last two typologies were distinguished in that the main purpose of an avenue is the movement of people, while the main purpose of a highway is the transportation of goods. access.[52]​.

Roman roads fell into disrepair in medieval Europe due to a lack of resources and knowledge to maintain them, but many continued to be used. The alignments are still partially used today, such as on parts of England's Route A1. Before the 19th century, there were no organized networks of streets within cities, and only passing paths. With the invention of the harness "Harness (garrison)" and cars with pivoting front axles, which allowed making tight curves, street networks in cities were established.[15]​.

In medieval Islam, numerous roads were built in the Arab Empire. The most sophisticated were those of Baghdad, in Iraq, paved with tar in the 19th century. The tar was obtained from oil from the existing springs in the region, through distillation.[16]​.

A medida que los estados de Europa se desarrollaban y enriquecían, especialmente durante el Renacimiento, comenzaron a construirse nuevas carreteras y puentes, a menudo basados en los diseños romanos. Aunque se produjeron intentos de redescubrir los métodos romanos, hubo poca innovación útil en la construcción de carreteras antes del siglo .

En el siglo , el transporte por carretera en el Imperio asante (en el África Occidental) se mantenía a través de una red de caminos bien mantenida que conectaba la capital del imperio con los territorios bajo su jurisdicción e influencia.[17]​[18]​ Tras la importante construcción de carreteras realizada en el Reino de Dahomey, se estableció un sistema de peaje, con la función de recaudar impuestos anuales basados en las mercancías transportadas por el Camino Real,[19]​ que fue construido a finales del siglo por el rey Kpengla, extendiéndose desde Abomey hasta Ouidah pasando por Cana.[20]​.

Entre 1725 y 1737, el general George Wade construyó una carretera de 250 millas (402,3 km) que contaba con 40 puentes, para mejorar el control de Gran Bretaña sobre las Tierras Altas de Escocia, utilizando diseños de calzadas romanas con grandes piedras en la base y grava en la parte superior, con una profundidad total de dos metros. La calzada estaba tan mal alineada y era tan empinada, según Thomas Telford, «que era inadecuada para la vida civil», además de ser irregular y con mal drenaje.[21]​.

Toll roads

In England, responsibility for the condition of roads lay with each local parish since Tudor times. In 1656, the parish of Radwell (Hertfordshire) petitioned Parliament for help in maintaining its section of the Great Northern Road.[22] Parliament passed an act giving local magistrates the power to erect tolls on a section of the Great Northern Road, between Wadesmill (Hertfordshire); Caxton (Cambridgeshire) "Caxton (Cambridgeshire)"); and Stilton "Stilton (Cambridgeshire)") (Huntingdonshire), for a period of eleven years. The revenue thus raised would be used to maintain the Great Northern Highway in their jurisdictions.[22][23] The toll erected at Wadesmill became the first effective toll in England.

El primer sistema con fideicomisarios que no eran jueces se estableció mediante una ley de peajes en 1707, para un tramo de la carretera Londres-Chester entre Fornhill y Stony Stratford. El principio básico era que los fideicomisarios gestionarían los recursos de las diversas parroquias por las que pasaba la carretera, los complementarían con los peajes de los usuarios de fuera de las parroquias y destinarían la totalidad al mantenimiento de la carretera principal. Esto se convirtió en el modelo para la construcción de peajes en un número creciente de carreteras, solicitado por quienes deseaban mejorar el flujo comercial a través de su parte del condado.[22]​.

At the turn of the century, sections of major radial roads leading to London were placed under the control of individual toll road trusts. The pace of creation of new toll roads accelerated in the 1750s, with the creation of trusts to maintain the transverse routes between the Great Highways radiating from London. Roads leading to some provincial towns, especially in the west of England, were placed under individual trusts, and key roads in Wales became toll roads. In South Wales, the roads of entire counties were placed under individual trusts in the 1760s. A new surge in trust formation took place in the 1770s, with the introduction of tolls for subsidiary connecting roads, routes over new bridges, new routes in growing industrial areas and highways in Scotland. By 1750 some 150 trusts had been established; By 1772, another 400 had been established, and by 1800, there were more than 700.[24] By 1825, some 1,000 organizations controlled 18,000 miles (28,968.1 km) of roads in England and Wales.[25]

The laws of these new trusts and the renewal laws of the previous ones incorporated a growing list of powers and responsibilities. Beginning in the 1750s, laws required trusts to construct milestones indicating the route and distance in miles between major towns on the road. Users were required to follow traffic rules, such as driving on the left, and not to damage the road surface. Trusts could charge additional tolls during the summer to pay for road irrigation needed to reduce dust raised by vehicles. Parliament also passed some general toll road laws addressing trust administration and restrictions on wheel width, as narrow wheels caused considerable damage to the road.

The quality of early toll roads varied.[26] While their construction involved some improvement to each road, the technologies used to address geological features, drainage, and the effects of climate were in their early stages. Road construction improved slowly, initially through the individual efforts of some engineers such as John Metcalf&action=edit&redlink=1 "John Metcalf (engineer) (not yet drafted)") in Yorkshire in the 1760s. British toll road builders[27]​ began to understand the importance of selecting clean stones for paving and excluding plant material and clay to achieve smoother roads. durable.[21][28]​.

Highways built in the United States used to be built by private companies under a government franchise. They tended to parallel or replace existing routes with a certain volume of trade, with the hope that the improved road would divert enough traffic to make the investment made profitable. Plank-paved roads were particularly attractive, as they greatly reduced rolling resistance and mitigated the problem of waterlogging. Better grading to soften the slope of the most difficult sections allowed draft animals to carry heavier loads.

Metcalf

The first professional road builder to emerge during the Industrial Revolution was John Metcalf&action=edit&redlink=1 "John Metcalf (engineer) (not yet drafted)"), who built approximately 180 miles (289.7 km) of toll roads, mainly in the north of England, beginning in 1765, when Parliament passed an act authorizing the creation of toll trusts to build toll-financed roads in the area of Knaresborough. Metcalf was awarded a contract to build a three-mile (5 km) stretch of road between Minskip and Ferrensby, as part of a new road that would connect Harrogate and Boroughbridge. He explored the rural area alone and calculated the most practical route.

He believed that a good road should have good foundations, good drainage, and a smooth convex surface to allow rainwater to drain quickly into the side ditches. He understood the importance of good drainage, knowing that rainfall was the cause of most road problems. He found a way to build a road through a bog using fajinas, tied bundles of calluna (a type of heather) and gorse branches as foundations. This cemented his reputation as a road builder, as other engineers believed it was impossible. He mastered his craft with his own method of calculating costs and materials, which other engineers did not understand.

Trésaguet

Pierre-Marie-Jérôme Trésaguet") is widely credited with establishing the first scientific method for road construction in France. In 1775, he wrote a memorandum on his method, which became general practice in his country. It consisted of a layer of large rocks covered by a smaller layer of gravel. The bottom layer improved on Roman practice, as it was based on the idea that the purpose of this layer (the subbase) is to transfer the weight of the road and from traffic to the ground, while protecting it from deformation by distributing the weight evenly. Therefore, the subbase did not have to be a self-supporting structure. The upper running surface provided a smooth surface for the vehicles, while protecting the large stones of the subbase.

Trésaguet understood the importance of drainage through the construction of deep lateral ditches, but he also insisted that his roads be accessible from the sides, which prevented the provision of the aforementioned ditches. Well-maintained surfaces and drains protect the integrity of the subbase, and Trésaguet introduced a continuous maintenance system, whereby each road worker was assigned a section of road to keep in optimal condition.[29]​.

Telford

The surveyor and engineer Thomas Telford made substantial advances in the engineering of new roads and the construction of bridges. Its construction method consisted of excavating a large trench, on which a solid rock foundation sat. He designed his roads with a downward slope from the center (crown slope or camber), which allowed drainage of the road surface layers, an important improvement over Trésaguet's work. The surface consisted of crushed stone. He improved road construction methods by optimizing stone selection based on thickness, taking traffic, alignment and slopes into account. During his final years, Telford was responsible for the reconstruction of sections of the London to Holyhead road, a task completed by his assistant of ten years, John MacNeill.

His engineering work in the 1820s on the Holyhead road (precedent of the A5 motorway), reduced the travel time of the "Stagecoach (coach)") from 45 hours to just 27 hours, and the best speeds of the mail carriages increased from 5-6 mph (8-10 km/h) to 9-10 mph (14-16 km/h). Between London and Shrewsbury, most of his road work consisted of improvements. Beyond Shrewsbury, and especially after Llangollen, the work often involved building a toll road from scratch. Notable features of this section of the route include the Waterloo Bridge across the River Conwy at Betws-y-Coed, the ascent from there to Capel Curig, and then the descent from the Nant Ffrancon Pass towards Bangor ("Bangor (Wales)"). Between Capel Curig and Bethesda "Bethesda (Gwynedd)"), in the Ogwen Valley, Telford deviated from the original road, built by the Romans during their occupation of this area.[30]​.

McAdam

It would be another Scottish engineer, John Loudon McAdam, who designed the first modern roads. He developed an inexpensive paving material based on an aggregate of crushed stone and earth (known as macadam). His method of road construction was simpler than Telford's, and also more effective in protecting the tracks: he discovered that massive foundations of successive layers of rock were unnecessary, and claimed that the natural soil alone would support the road and traffic, provided it was covered by a crust that protected the underlying soil from water and wear.[31]

Unlike Telford and other road builders, McAdam laid out his roads as level as he could. Its 30-foot (9.1 m) wide road only required a 3-inch (7.6 cm) lift from the edges to the center. The banking and elevation of the road above the water table allowed rainwater to drain into the ditches on both sides.[33]​.

The size of the stones was fundamental to McAdam's theory of road construction. At the lower road thickness of 200 millimeters (7.9 in), the size of the stones was limited to less than 75 millimeters (3 in). The top layer of 50 millimeters (2 in) thick stones was limited to a size of 20 millimeters (0.8 in), and the stones were checked by supervisors with scales. A worker could quickly check the minimum allowable size of the stone for himself, seeing if it would fit in his mouth. The importance of the 20 mm size of the road course was that these stones had to be much smaller than the 100 mm wide iron wheels of the carriages that circulated on the road.

McAdam believed that the "proper method" of breaking stones, for convenience and speed, was for people to sit and use small hammers, breaking the stones so that none weighed more than six ounces. He wrote that the quality of the road would depend on the care with which the stones were spread over the surface over a considerable space, shovel by shovel.[34]​.

He also indicated that no substance that would absorb water should be incorporated, as it could affect the path in case of frost, nor should anything be placed on the clean stone to consolidate it. The action of road traffic caused the broken stone to combine with its own angles, forming a solid, level surface that would resist weather and traffic.[35] From his experience in road construction, McAdam had learned that a layer of broken cornerstones would act as a solid mass and would not require the large layer of stone previously used to build roads. By keeping stones smaller than the width of the wheel on the surface, a good rolling surface for traffic could be created. The small surface stones also provided little stress on the road, provided they were kept reasonably dry.[36]​ In practice, their roads proved to be twice as strong as those at Telford.[37]​.

Although McAdam had been adamantly opposed to filling the gaps between his small cut stones with smaller material, in practice road builders began to introduce filler materials, such as smaller stones, sand or clay, and it was noted that these roads were stronger as a result. "Macadam" roads were widely built in the United States and Australia in the 1820s and in Europe in the 1830s and 1840s.[38] These roads were suitable for use by horses and carriages or stagecoaches, but were very dusty and prone to erosion in heavy rain.

El Good Roads Movement fue un movimiento que se desarrolló en los Estados Unidos entre finales de la década de 1870 y la de 1920. Los defensores de la mejora de las carreteras, liderados por los ciclistas asociados a la Liga Americana, transformaron la agitación local en un movimiento político nacional. Fuera de las ciudades, las carreteras eran de tierra o de grava, con barro en invierno y polvo en verano. Los primeros organizadores tomaron como ejemplo el caso de Europa, donde la construcción y el mantenimiento de carreteras contaban con el apoyo de numerosos gobiernos nacionales y locales. En sus inicios, el objetivo principal del movimiento era promover la construcción de carreteras en las zonas agrícolas situadas entre las ciudades, y ayudar a las poblaciones rurales a obtener los beneficios sociales y económicos que se disfrutaban en las ciudades, donde los residentes se beneficiaban de ferrocarriles, tranvías y calles pavimentadas. Incluso más que los vehículos tradicionales, las bicicletas, recién inventadas, podían beneficiarse de las buenas carreteras rurales.

Más adelante, se vio que las carreteras de macadán no resistían el paso de vehículos cada vez más rápidos y pesados. Los métodos para estabilizar carreteras con brea se remontan al menos a 1834, cuando John Henry Cassell, al frente de la compañía "Cassell's Patent Lava Stone Works" del barrio londinenese de Millwall, patentó el "Pitch Macadam".[39]​ Este método consistía en extender alquitrán sobre una subbase granular, colocar encima una capa típica de macadán y, finalmente, sellarlo con una mezcla de alquitrán y arena. El macadán con lechada de alquitrán se utilizaba mucho antes de 1900 e implicaba escarificar la superficie de un pavimento de macadán existente, extender el alquitrán y volver a compactarlo. Aunque el uso del alquitrán en la construcción de carreteras ya se conocía en el siglo , se utilizaba poco y no se introdujo a gran escala hasta la llegada del automóvil a principios del siglo .

El tarmacadam o macadán asfáltico moderno fue patentado por el ingeniero civil británico Edgar Purnell Hooley"), quien observó que el alquitrán vertido sobre una calzada de macadán retenía el polvo y creaba una superficie lisa.[40]​ En 1901, obtuvo una patente para el procedimiento de asfaltado.[41]​ La patente de Hooley de 1901 implicaba la mezcla mecánica de alquitrán y áridos antes de su colocación y la posterior compactación de la mezcla con una apisonadora de vapor. El alquitrán se modificaba añadiendo pequeñas cantidades de cemento Portland, resina y/o brea.[42]​.

Controlled access highways

The first version of modern highways was developed during the first half of the century. The Long Island Motor Parkway in Long Island, New York "New York (state)"), opened in 1908 as a private initiative, was the world's first limited access highway. It included numerous modern features, such as banked curves, safety barriers, and asphalt concrete pavement.[45] Traffic could turn left between the main roadway and off-ramps, crossing oncoming traffic, so it was not a controlled-access highway (or a "expressway" proper, as later defined by the United States federal government's "Manual on Uniform Traffic Control Devices").

Modern controlled-access highways emerged in the early 1920s in response to rapidly increasing automobile use, growing demand for faster transportation between cities, and improvements in paving processes, techniques, and materials. These original high-speed roads, known as expressways, have been modernized and are still in use.

Italy was the first country in the world to build controlled access highways reserved for fast traffic, and only for motor vehicles.[43]​[44]​ The Autostrada A8 ("Lake Highway"), the first highway built in the world, connected Milan with Lake Como and Lake Maggiore, and was later integrated into the A8 and A9 motorways. It was designed by Piero Puricelli and opened in 1924.[44] This highway, originally called *autostrada"), contained only one lane in each direction and lacked interchanges. The Bronx River Parkway was the first highway in North America to use a strip in the median to separate opposing lanes. It was built through a park, and the streets that crossed it were crossed by bridges.[46][47]​ The Southern State Parkway opened in 1927, while the Long Island Motor Parkway closed in 1937 and was replaced by the Northern State Parkway (opened in 1931) and the adjacent Grand Central Parkway (opened in 1936). In Germany, construction of the Bonn-Cologne Autobahn began in 1929 and was opened in 1932 by Konrad. Adenauer, then mayor of Cologne "Cologne (Germany)").[48]​.

In Canada, the first pioneer highway with semi-controlled access was The Middle Road between Hamilton "Hamilton (Ontario)") and Toronto, which featured a median divider between opposing traffic flows, as well as the country's first cloverleaf interchange. This highway became the Queen Elizabeth Way, which had a cloverleaf and a trumpet interchange when it opened in 1937 and, until the Second World War, had the longest illuminated stretch of highway ever built.[49] A decade later, the first section of Ontario's Highway 401, based on earlier designs, opened. Since then, it has become the busiest highway in North America.

The term freeway was first used in February 1930 by Edward M. Bassett,[50]​[51][52]​ who argued that roads should be classified into three basic types: highways, avenues, and roads.[52]​ In Bassett's system, based on zoning and property rights, the owners of adjoining properties had the right to continue receiving sunlight, dominion over the vertical flight of their plots and access to the road; but not from avenues or highways. These last two typologies were distinguished in that the main purpose of an avenue is the movement of people, while the main purpose of a highway is the transportation of goods. access.[52]​.