Transport Planning and Traffic Engineering

Coleman A. O'Flaherty, Coleman A. O'Flaherty

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781136352362
• Edition: 1
• Topic: Tecnologia e ingegneria
• Subtopic: Ingegneria civile

'Transport Planning and Traffic Engineering' is a comprehensive textbook on the relevant principles and practice. It includes sections on transport policy and planning, traffic surveys and accident investigation, road design for capacity and safety, and traffic management. Clearly written and illustrated, the book is ideal reading for students of transport, transport planning, traffic engineering and road design.

PART I

Planning for transport

CHAPTER 1

Evolution of the transport task

C.A. O’Flaherty

Everybody travels whether it be to work, play, shop or do business. All raw materials must be conveyed from the land to a place of manufacture or usage, and all goods must be moved from the factory to the market place and from the staff to the consumer. Transport is the means by which these activities occur; it is the cement that binds together communities and their activities. Meeting these needs has been, and continues to be, the transport task.

Transport, because of its pervasive nature, occupies a central position in the fabric of a modern-day urbanised nation. To understand this it is useful to consider how today’s land transport system, and particularly its road system, has developed over time. In Britain, as in most countries, this has been a story of evolutionary change with new transport developments replacing the old in response to perceived societal and economic needs. How people live and work has also changed as a consequence of improvements in lifestyle and in transport capabilities. What can be said with certainty about the future is that these interactive changes will continue, and that it will be the task of the transport planner and traffic engineer to cope with them.

Because of the pervasiveness of transport, ‘solutions’ to transport problems can have major influences upon people’s lives. These influences are reflected in the constraints which society currently places on the development and evaluation of road proposals; that is, generally, they must be analytically based, economically sound, socially credible, environmentally sensitive, politically acceptable and inquiry proof. Meeting these needs has resulted in the development in relatively recent times of a new professional area, transport engineering.

Transport engineering applies technological and scientific principles to the planning, functional design, operation and management of facilities for any mode of transport in order to provide for the safe, rapid, comfortable, convenient, economical, and environmentally compatible movement of people and goods. Traffic engineering, a branch of transport engineering, deals with the planning, geometric design, and traffic operation of roads, streets, and highways, their networks, terminals, abutting land, and relationships with other modes of transport.

1.1 The road in history

The birth of the road is lost in the mists of antiquity. However, with the establishment of permanent settlements and the domestication of animals some 9000 years ago, the trails deliberately chosen by people and their animals were the forerunners of the first recognised travelways which, in turn, evolved into today’s streets, roads and highways.

Although the wheel was invented in Mesopotamia ca 5000 BC, it did not come into wide usage as a carrier of humans or goods until well into the second millennium AD. For thousands of years, therefore, the transport task was carried out by humans and pack animals walking to their destinations. On long trips people rarely walked more than 40 km in a day and, consequently, settlements tended to develop about well-used resting places 15 to 40 km apart. Typically, these were at sites which had reliable water supplies and were easily defended. These settlements, in turn, reinforced the establishment of recognised travelways between these sites. Many settlements, especially those at crossings of streams and/or travelways, or on dominant sites adjacent to waterways, eventually grew into villages and towns. Until the Industrial Revolution these settlements rarely exceeded 45 minutes’ travel by foot from the outskirts to their centres.

The first manufactured roads¹ were the stone-paved streets of Ur in the Middle East (ca 4000 BC), the corduroy log paths of Glastonbury, England (ca 3300 BC), and the brick pavings in India (ca 3000 BC).

The oldest extant wooden pathway in Europe, the 2 km Sweet Track, was built across (and parts subsequently preserved in) marshy ground near Glastonbury. Corduroy road sections have also been found in marshy ground in continental Europe. Many of these formed part of a comprehensive network of trade routes, the Amber Routes,² which developed over the period 4000 BC to 1500 BC.

The oldest extant stone road in Europe was built in Crete about 2000 BC. About 50 km long, its function was to connect the then capital Knossos in the north of the island with the southern port of Leben, thereby gaining access to the Mediterranean trade. However, notwithstanding the many examples of stone roads which have been found in various parts of the world, it is the early Romans who are now credited with being the first real roadmakers.

The Roman road system was based on 29 major roads, totalling 78 000 km in length, which radiated from Rome to the outer fringes of the Empire. The pavements were usually constructed at least 4.25 m wide to enable two chariots to pass with ease and legions to march six abreast. These roads were constructed by the military, using slave labour, to aid administration and enable the legions to march quickly to quell rebellion after an area had been occupied. They had long straight sections to minimise travel time, and often followed firmer and safer old travelways along the sides of hills. Many pavements were constructed on embankments up to 1 m, sometimes 2 m, high (for defence reasons) in locales where attacks were likely. Soil for the embankments was mostly obtained by excavating longitudinal drains on either side of the road; in soft soils foundations were strengthened by driving wooden piles. Stone pavements were laid with crossfalls to aid drainage, widened at bends to accommodate the unwieldy carts and wagons of the day, and reduced in width in difficult terrain.

Following their invasion of Britain in 55 BC, the Romans constructed some 5000 km of major road in 150 years. This road system radiated from their capital, London (located at the first upstream crossing of the Thames) and extended into Wales and north to beyond Hadrian’s Wall. The withdrawal of the last legion from Britain in 407 AD marked the final decline of the Roman Empire – and the breakdown for centuries of the only organised road system in Europe.

After about 100 years the Roman roads fell into decay from the wear and tear of natural and human forces. During the Dark Ages Britain was split into small kingdoms whose rulers’ needs were parochial rather than national, so they exerted little effort to preserve the through-roads. When sections became untraversable, trackways were simply created around them. New roads consisted of tracks worn according to need, with care usually being taken to avoid cultivated land and private property. These practices largely account for the winding nature of many of Britain’s present-day roads and lanes.

Throughout the Middle Ages through-roads were nothing more than miry tracks, and the rivers and the seas tended to be relied upon as the main trade arteries. This was in contrast with the situation in continental Europe, especially in France whose centralist rulers built main roads radiating from Paris as a means of holding the country together. The only significant commitment to road works in Britain was by the medieval religious authorities, who saw road repairs as meritorious work similar to that of caring for the poor and the sick. The suppression of the monasteries by Henry VIII removed these road maintainers, however, and the new owners of the ecclesiastical estates were not inclined to continue their road obligations.

1.1.1 Emergence of passenger transport

A feature of the Middle Ages was the growth of many prosperous villages into towns. Consequently, lengths of stone-paved street were constructed within some of the larger towns. The building of these roads was often associated with the need to provision towns from their rural hinterlands, i.e. good access roads were needed to withstand the high wheel pressures created by wagons and carts (and eventually, coaches with passengers).

The first non-ceremonial coach to be seen in Britain appeared in London in 1555. However, Milan led Europe in the development of urban coach travel, with 60 coaches in use in 1635.¹ Long wagon-coaches were in use in Spain as early as 1546 to provide for long-distance passenger travel.

The first British stagecoach to stop at regularly-spaced posthouses to change horses operated between Edinburgh and Leith in 1610. The development (in Austria) in the 1660s of the Berliner coach with its iron-spring suspension system led to the rapid expansion of coach-type travel so that, by 1750, four-wheeled coaches and two-wheeled chaises (introduced from France) had superseded horseback-riding as the main mode of intertown travel for Britain’s wealthy and the growing middle class. This expansion of coach travel was facilitated by major initiatives in road-making, initially in France and then in Britain.

At the turn of the eighteenth century Britain’s roads were so abominable that Parliament passed in 1706 the first of many statutes which created special bodies known as Turnpike Trusts. These Trusts, which eventually exceeded 1100 in number and administered some 36 800 km of non-urban roadway, were each empowered to construct and maintain a designated length of road and to levy tolls upon specified kinds of traffic. The development of the toll road system, particularly in the century following 1750, was important for a number of reasons: first, it resulted in the emergence of skilled road-makers, e.g. John Metcalf, Thomas Telford, John Loudon McAdam; second, it established that road-users should pay road costs; third, it determined the framework of the present-day main road network; and fourth, it made coach travel quicker, easier, more comfortable, and more attractive.

By the turn of the nineteenth century the value of road drainage and of firm roads with solid surfaces was widely accepted and many thousands of kilometres of good quality main road had been built between towns. In urban areas heavily-trafficked main streets were surfaced with stone setts. Wooden blocks were often used instead of stone setts to alleviate the noise and unhygienic pollution engendered by animal-drawn iron-tyred vehicles. Whilst these block roads were relatively easy to sweep, they were slippery when wet, smelly, and had fairly short lives. Thus it was not until steel tyres were replaced by pneumatic tyres (patented by Robert Thompson in London in 1845 and made workable by John Dunlop in 1888) and streets were surfaced with ‘artificial’ bituminous asphalt (mainly from the turn of the twentieth century) that these early environmental pollution problems were alleviated.

1.2 Railways, bicycles and motor vehicles

With the advent of the industrial revolution, there was a great wave of migration from the countryside and villages became towns and towns became cities. This was accompanied by a population explosion resulting mainly from improved living and health conditions; for instance, in 1800 the population of England and Wales was less than 10 million (ca 17 per cent lived in towns of more than 20 000 populatio...