Road junctions and intersections

A road junction is the point at which one road meets another; an intersection is the point at which two or more roads cross еach other. Both junctions and intersections are the worst danger spots in a road system.

The problems of reducing danger at these points are those of cost and space. If junctions and intersections are such that all classes of traffic meet each other at the same level, there is a danger of collision. Almost complete segregation of different classes can be achieved, and the need for users of the same class to cross traffic streams can be avoided.

Пособие по английскому языку для студентов II-III курсов строительных вузов / М.: Высш. школа, 1978. – C.20

The perfect example of complete segregation of different classes of traffic and of the avoidance of crossing traffic streams is the clover-leaf junction, at which no collision can occur between vehicles.

All forms of road junction can be classified into three groups: multi-level junctions, roundabouts and flyover-junctions.

Multi-level junctions. The clover-leaf, the most typical of these, has already been mentioned. There is need for multi-level intersections where three conditions are fulfilled:

· only a small percentage of the traffic must turn to left or right

· the major volume of traffic is travelling on a fast through route

· the volume of traffic would otherwise be sufficient to justify the provision of a roundabout.

Roundabouts. Unlike multi-level intersections, roundabouts do not enable traffic to cross without dropping speed but pedestrians and cyclists cannot be segregated unless costly over- or under-passes are constructed.

Пособие по английскому языку для студентов II-III курсов строительных вузов / М.: Высш. школа, 1978. – C.21

The success of a roundabout depends greatly upon the ease with which vehicles using it can “weave” or pass from one traffic lane to another. The greater the length of the road in which the weaving can be carried out and the smaller the angle of approach of converging streams of traffic, the more easily can weaving be performed. The angle should not be greater than 30 degrees. The greater the diameter of the island, the smaller the angle of convergence.

Flyover-junctions.These have been developed chiefly at places where there are no pedestrians. These “flyovers”, which enable high speeds to be maintained, are extremely expensive, costing about ten times as much as roundabout, so it is much better to have ten roundabouts at ten dangerous junctions than a single flyover at a single junction. A combination of roundabout and flyover bridge can be of great value.

Road signs

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Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest road signs were milestones, giving distance or direction; for example, the Romans erected stone columns throughout their empire giving the distance to Rome.

In the Middle Ages, multidirectional signs at intersections became common, giving directions to cities and towns.

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The first modern road signs erected on a wide scale were designed for riders of high or “ordinary” bicycles in the late 1870s and early 1880s. With traffic volumes increasing since the 1930s, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to overcome language barriers, and enhance traffic safety. Such pictorial signs use symbols in place of words and are usually based on international protocols. Such signs were first developed in Europe, and have been adopted by most countries to varying degrees. Pre-industrial signs were stone or wood. In the late 18th and 19th centuries painted cast iron became popular. Since 1945 most signs have been made from sheet aluminium with adhesive plastic coatings, these are normally retroreflective for night-time and low-light visibility. Before the development of reflective plastics, reflectivity was provided by glass reflectors set into the lettering and symbols.

New generations of traffic signs based on electronic displays can also change their text (or, in some countries, symbols) to provide for “intelligent control” linked to automated traffic sensors.

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Traffic signs can be grouped into several types. For example, Annexe 1 of the Vienna Convention on Road Signs and Signals (1968), which on 30 June 2004 had 52 signatory countries, defines eight categories of signs:

A. Danger warning signs

B. Priority signs

C. Prohibitory or restrictive signs

D. Mandatory signs

E. Special regulation signs

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F. Information, facilities, or service signs

G. Direction, position, or indication signs

H. Additional panels

Traffic control

It is obvious that in existing urban areas much of the congestion is due to narrow streets and junctions which are incapable of taking peak-hour traffic. The solutions of this problem are costly. They include adequate roundabouts and street widening and the segregation of traffic by means of flyover roads, underpasses, bridges and pedestrian subways.

Much of the congestion in urban areas is due to traffic which has no business in the area but is only passing through.

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There is a tendency for drivers to keep to the well-lit shopping streets. If they can be made to use less important streets and those not occupied by shops, then conditions are improved not only for the through traffic but also for the local traffic.

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Signposting is, of course, a directional control and a very effective one. In fact it is important for all signs and symbols used on the roads to be seen well in advance by drivers approaching at normal speed. Directional control cannot increase the capacity of the highway system but it can avoid local congestion.

One-way traffic is a special kind of directional control which is very effective in maintaining the traffic flow in congested areas.

A major cause of congestion in towns is the interruption to the free flow of traffic by cross traffic at junctions. But if the need for traffic streams to cross each other can be avoided then the movement of vehicles will be much easier. This easier movement of traffic can often be achieved by making traffic move in one direction only along certain streets and by prohibiting incoming vehicles from side streets from crossing the main stream. The streets may be either one-way or two-way according to local conditions of traffic or width of carriageway, and traffic at the junctions can be guided by constructing suitably-shaped islands. Besides, one-way traffic can also be introduced where the carriageway width is inadequate for two opposing lines of traffic.

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The disadvantages of a one-way traffic system are that it increases the distance travelled by some vehicles, that it makes it more difficult for strangers to find their way about. The true aim of a one-way system is to eliminate cross traffic, and under conditions of continuous flow on crossing streets the introduction of a properly designed one-way scheme can double the carrying capacity of the highways.

The two main objections to street intersections are that they are a cause of accidents and that they interrupt the flow of traffic. The best thing to do with intersections is to get rid of them. If that is not possible they may be improved and made safer but they will always remain a source of danger and delay.

Many accidents are caused because traffic streams of different types, or traffic streams travelling in different directions are using the same carriageway, and these accidents can be avoided either by reservations between traffic lanes, or by vertical (or “grade”) separation.

In many cities in America and in Europe segregation of traffic is achieved by means of flyovers or underpasses; at some junctions there are even three different levels. Each has its advantages and disadvantages according to the circumstances. Flyover structures are not always aesthetically pleasing while an underpass may be more expensive to construct. The separation of fast and slow traffic from the heavier and faster traffic is most desirable not only in the interests of freedom of traffic movement, but also of safety. This ideal is not easy to achieve.

Urban traffic control will be of benefit to the general public in the district concerned and will result in greater comfort for road users of all classes, as well as bringing economic advantages to the community as a whole.

Road safety

Road traffic safety refers to methods and measures for reducing the risk of a person using the road network being killed or seriously injured. The users of a road include pedestrians, cyclists, motorists, their passengers, and passengers of on-road public transport, mainly buses and trams. Best-practice road safety strategies focus upon the prevention of serious injury and death crashes in spite of human fallibility. Safe road design is now about providing a road environment which ensures vehicle speeds will be within the human tolerances for serious injury and death wherever conflict points exist.

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On existing urban roads where many vulnerable road users, such as pedestrians and bicyclists can be found, traffic calming can be a tool for road safety. Though not strictly a traffic calming measure, mini-traffic circles implanted in existing, normal intersections of urban streets, have been shown to reduce collisions at intersections dramatically. Shared space schemes, which rely on human instincts and interactions, such as eye contact, for their effectiveness, and are characterised by the removal of traditional traffic signals and signs, and even by the removal of the distinction between roadway and footway, are also becoming increasingly popular. Both approaches can be shown to be effective.

Major highways are designed for safer high-speed operation and generally have lower levels of injury per vehicle km than other roads.

Safety features include:

· Limited access from properties and local roads.

· Grade separated junctions

· Median dividers between opposite-direction traffic to reduce likelihood of head-on collisions

· Removing roadside obstacles.

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Prohibition of more vulnerable road users and slower vehicles.

Modern safety barriers are designed to absorb impact energy and minimize the risk to the occupants of cars, and bystanders. For example some road fixtures such as road signs and fire hydrants are designed to collapse on impact. Highway authorities have also removed trees in the vicinity of roads; while the idea of “dangerous trees” has attracted a certain amount of skepticism, unforgiving objects such as trees can cause severe damage and injury to any road users.

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