17. Road traffic

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1. Scope

1.1 Function of roads
1.2 Road traffic media
1.3 Purpose of the brief

2. Environmental impacts and protective measures

2.1 Emissions from road traffic
2.2 Traffic safety
2.3 Reducing road traffic and transfer to other transport media through regional development planning and an integrated transport concept
2.4 Administrative, regulatory and financial measures

3. Notes on the Analysis and Evaluation of Environmental Impacts

4. Interaction with other sectors

5. Summary assessment of environmental relevance

6. References


1. Scope

1.1 Function of roads

This environmental brief deals with the environmental burdens imposed by road traffic, i.e. by the transport of persons or goods on highways and other roads. The effects of road building are dealt with in a separate environmental brief (Road Building).

Roads are used not only to relocate persons and goods - in other words, purely for transport or traffic purposes - but also have residential and access functions. While roads generally perform traffic functions outside urban areas, town and village roads play an important part in the residential function. Accordingly, the term "environment" is not limited to the natural surroundings to the same extent as in undeveloped areas. Rather, the aim is to ensure that traffic can be managed in a way which is compatible with the urban situation - in other words, in a way that is also socially acceptable. This means that transport and traffic planning must also take account of traditional lifestyles specific to the region.

1.2 Road traffic media

By far the majority of the harmful effects inflicted on the environment by road traffic are caused by vehicular traffic (cars, heavy goods vehicles, buses and coaches, motorcycles). However, when considering urbanisation processes (BECKMANN [1], DIOU [2], TOLBA [3]), it is vital to note that the creation of a road environment which makes better provision for pedestrians and cyclists can help reduce environmental impact. Non-motorised traffic - as the most environment-friendly type of movement - traditionally accounts for a large proportion of total urban traffic in certain regions.

A strategy geared to the use of environment-friendly modes of transport will only have any prospect of success, however, if urban and regional development planning on the one hand, and methods of production (including sale and distribution) on the other take this into account. If either people or goods need to cover large distances, the opportunities for employing traditional means of transport will diminish.

1.3 Purpose of the brief

The aim of the brief in the first instance is to illustrate measures whereby the existing environmental impacts of motorised road traffic can be reduced by prevention or by operating them in a way favourable to the environment. In addition, the brief also provides information on environmental burdens caused by projects which induce traffic.


2. Environmental impacts and protective measures

One particular characteristic of the environmental damage caused by road traffic is that the impact is made up of a large number of minor individual factors. Sectors of the infrastructure connected with the traffic system (refineries, fuel transportation, workshops, dumps) also make a contribution. The assumption that these cause only a negligible fraction of the environmental burden will result in road users failing to change their customary behaviour in the way that is needed.

2.1 Emissions from road traffic

Although road vehicles, which mainly originate from industrialised countries, give off similar emissions when new, as required in the country of origin, they are generally maintained less well due to lack of supervision by the authorities and poor economic conditions. This means that the individual vehicle pollutes the environment more heavily for the same mileage, especially as regards the sharp rise in emissions from a poorly maintained engine (e.g. unburnt fuel, noise etc.) and leakage of water-polluting liquids (oil, fuel etc.). Poor quality fuels likewise produce higher levels of pollutants, and unleaded petrol is unobtainable in many countries.

(a) Air pollutants

Air pollutants are not only harmful to human beings, they can also present a hazard to animals, the soil, vegetation and the climate. Remote effects (i.e. remote both in time and in space) must be considered; one must also remember that combinations of air pollutants may be more harmful than the individual contaminants (synergetic effects). The principal air pollutants emitted by vehicular traffic are as follows:

- Carbon monoxide is not harmful to bloodless animals and plants, but sustained concentrations, even if small, can have an impact on both humans and other vertebrates. Compounds formed with the haemoglobin in the blood restrict the oxygen supply to the tissues, and in this way can cause disorders of the central nervous system.
- Certain hydrocarbons, resulting from incomplete fuel combustion (such as benzol), are carcinogenic among humans.
- Nitrogen oxides are irritants to human beings, and can damage the organs of respiration. In areas of high population density, nitrogen oxides contribute to smog formation. Plants are not directly damaged by nitrogen oxides at concentrations below 200 µg/m3 air [4].
- Under ultraviolet radiation, ozone is produced from nitrogen oxides and hydrocarbons. High ozone concentrations may cause smog and afflict the respiratory tract and circulation in humans. Moreover, ozone can cause serious damage to woodland and also, if present in sufficiently high concentrations, to crops such as vegetables and tobacco plants. Ethylene can have an unfavourable effect on the growth and ageing of plants. The numerous chemical interactions involved have not yet been fully explained.
- Lead and other heavy metals, which are deposited in the bones, are poisonous to humans and can cause disorders of the central nervous system. Lead aerosols are dispersed mainly over an area up to 30 to 50 metres from the roadway, while traces can be carried as far as 100 to 200 metres, depending on wind conditions. Plants absorb lead from the air by surface contact (dust deposits), or from the soil through their roots. As well as growth damage to the plant itself, follow-on effects through absorption into the food chain should also be noted (e.g. milk produced from pastures near busy roads).
- Soot burdens are mainly due to the high proportion of diesel engines, particularly among heavy goods vehicles. Soot emissions are substantially aggravated by inadequate vehicle maintenance. The danger posed by soot arises principally from the deposition of toxic combustion residues.

Carbon dioxide, which is released by the combustion of fossil fuels, is not a directly harmful gas, but it does increase the CO2 concentration in the earth's atmosphere. The solar radiation reflected on the surface of the earth is accordingly absorbed by the air, causing the air to heat up (the "greenhouse effect"). Unlike the other air pollutants, emission of the carbon dioxide responsible for the "greenhouse effect" cannot be reduced by catalytic converters.

Though developing countries' contribution to the "greenhouse effect" is still small by comparison with the industrialised nations, a comparison by the Worldwatch Institute of the levels of motorisation of Western industrialised nations and developing countries for 1986 (Figure 1) shows the consequences of a sharp increase in motor vehicle use, even if the level of motorisation of the industrial nations were not to be reached. The overall effects on the climate (and on oil consumption) would be intolerable. This means not only that industrialised countries' traffic conditions cannot simply be imported, but also that the industrialised nations must restrict private vehicle use, if developing countries are to be allowed any scope for increasing general living standards, without jeopardising climatic conditions and the supply of oil on a global scale.

Fig. 1 - Comparison of the degree of motorisation of the USA, Western Europe, Africa and China for 1986

The following causes of air pollutant emissions are of particular importance:

- inadequately maintained and elderly vehicles with increased pollutant output (carburettors, ignition, fuel injection systems, exhaust systems)
- deficient technical inspection and supervision of both fuel production and vehicles (emission tests)
- low quality fuels (unfavourable combustion processes)

The intensity of air pollution in a given area depends on:

- the volume of traffic,
- the ratio of internal combustion to diesel engines,
- driving habits (speed and gear selection as well as acceleration and braking behaviour),
- the condition of the engines,
- the quality of the fuel used,
- climatic and topographical conditions (air renewal).

(b) Noise

Noise is defined as all sounds which are "perceived by people as disturbing or oppressive" [6]. The consequences range from disturbances of general well-being or hindrance of speech comprehension to serious intrusions (disturbance of sleep, prevention of relaxation and interference with human performance) and illnesses (hearing impairment, damage to the cardiovascular system).

In addition to noise from engines and other vehicular sources (running and wind noise), individual driver habits (sounding the horn, slamming doors) all contribute to traffic noise. Vehicle noise also depends not only on the technical condition of the vehicle but also on individual driving behaviour (speed and gear selection, acceleration and braking).

Measures to prevent noise include the following:

- regular technical inspection of vehicles,
- selection of low-noise road surfaces,
- speed restrictions in relevant areas,
- road layout and gradients optimised to help avoid unnecessary gear changes,
- reduction of through-traffic in the vicinity of town centres, residential areas, hospitals, schools and places of worship, as well as other areas sensitive to noise,
- restricted access at certain times to protected areas (e.g. heavy goods vehicles banned from inner urban areas at night),
- driver education, for lorry drivers in particular, but also for bus and coach drivers.

Many countries have no noise abatement laws. Vehicles and driving habits there will long continue to produce an unnecessary amount of noise compared with standards in the industrialised nations. Periodic vehicle inspections and bans on night driving, sounding horns etc. can only be introduced gradually, if at all. Noise measurements or passive noise protection measures such as noise-abating embankments, walls or windows are only feasible in special cases.

Nevertheless, it is essential to work towards long-term reduction of noise from road traffic through primary noise abatement measures. Secondary noise reduction, as governed by guidelines in the Federal Republic of Germany, is difficult to implement in many countries (due to cost, administrative effort etc.).

(c) Wear and oil losses

The frequently uneven and rough road surfaces cause wear on tyres and road coverings, which contain poisonous substances. Wear on brake and clutch linings may give off highly toxic substances such as nickel and asbestos. Unmade road surfaces are sources of irritant dust which increases the risk of accidents and, in the absence of rainfall, may adversely affect vegetation. Oil often leaks from the engines and pipes of poorly maintained vehicles.

One particular problem is poor drainage, which may cause pollutants in wear products and also oil leaking from pipes and engines to be discharged into the environment during periods of rainfall, thereby endangering not only the soil but also the groundwater.

By contrast with air pollutants, toxic wear products and oil are not directly harmful to humans, but can indirectly deprive them of the conditions on which life depends if the land can no longer be worked without risk to health or is no longer habitable.

Only part of the damage caused by vehicle emissions referred to under (a) to (c) can be reduced and limited, if not eliminated altogether, by regular inspection of vehicles, monitoring and improvement of fuels and concentration of traffic in particular areas. The best way to achieve a lasting reduction is to reduce the volume of road traffic, something which should be aimed for in order to protect the earth's atmosphere (see above). The following measures might be considered as incentives to this end (see also the environmental brief Transport and Traffic Planning):

- petroleum tax,
- emission-based vehicle tax,
- road tolls,
- access restrictions at certain times,
- inner city parking restrictions,
- fiscal incentives for vehicle user-groups
- separate lanes for local public transport vehicles and vehicle user-groups (e.g. joint use of bus lanes).

(d) Energy consumption

At present nearly all motor vehicles require petroleum-based fuels. In many countries, not just the transport sector but rather the entire energy sector depends on petroleum. Because the overwhelming majority of these countries need to import most, if not all, of their petroleum requirement [4], promoting vehicle traffic at the expense of other sectors would mean devoting substantial resources to fuel supplies, thereby depriving other sectors of energy supplies. This could in turn prevent the sought-after rise in living standards, despite the expansion of the transport system.

Where there is no alternative to using motor vehicles, economical vehicles with minimal fuel consumption or driven by alternative fuels should be used. While the exclusive use of plant matter as a fuel substitute is problematic because of competition with foodstuffs (as in Brazil), bio-fuels derived from waste products do offer a solution (e.g. the biogas buses used in China, see [7]). In countries where electricity can be generated cheaply by hydroelectric plants, particularly in urban areas, the possibility of using electrically driven vehicles (trams, electric buses, dual system buses) should be investigated. The use of liquid gas as a coupled product from refineries would reduce petroleum consumption and pollutant emissions.

In the passenger transport sector, every effort should be made to meet transport demand with trams or buses which, with the appropriate number of passengers, have a lower specific energy consumption than private cars. For short journeys, optimum conditions should be created for pedestrians and cyclists. Town planners should furthermore aim to include or create structures enabling people to reach their destinations on foot or by bicycle. People should not be forced to travel long distances by doing away with mixed areas in favour of widely separated areas devoted exclusively to e.g. housing, working, recreation, administration etc.

2.2 Traffic safety

Because of its importance, traffic safety is not usually subsumed under the heading of the "environment", being regarded as a sector in its own right. Nevertheless, traffic safety, which covers more than the prevention of accidents, is an important aspect of the quality of life, and therefore needs to be discussed here.

A vital means of reducing the risk of accidents for all groups of transport users is the imposition of vehicle speed restrictions, which differ according to locality (highways outside urban areas, main traffic routes in town and city centres, access routes etc.), and according to the state of development and condition of the road.

In addition, the accident risk can be reduced by intensive road safety training, technical inspection of the vehicles, tougher safety regulations (such as the mandatory wearing of seatbelts, driving tests administered by properly qualified persons or the banning of drink-driving). Furthermore, efforts should be made to improve the working conditions of professional drivers, particularly lorry drivers. Appropriate measures include not only requiring certain standards of comfort in the "workplace" (e.g. heat-shielding vehicle roofs), but also properly supervised driver working hours so as to prevent accidents due to fatigue.

Accidents involving hazardous goods transports can put not only human beings and animals at risk, but can also cause local environmental damage on a considerable scale. The same applies to the escape of hazardous substances during regular journeys. In particular, there is a risk of contamination of watercourses and groundwater.

Serious damage and severe curtailment of the service life of road surfaces is caused by overloading (an axle loading increased by 30 % trebles the stress on the sub-base); this may increase the risk of accidents. To repair the damage (usually with a complete new bituminously bonded roadway surface) is not only expensive but also uses up valuable natural resources.

2.3 Reducing road traffic and transfer to other transport media through regional development planning and an integrated transport concept

A transport master plan is needed, coordinated with the regional development plan, concentrating primarily on making transport more environment-friendly and less costly to the national economy as a whole. This can be done by observing the following principles (see also environmental brief Transport and Traffic Planning):

I) Decentralisation of residential, industrial and supply facilities, with the aim of reducing transport distances;

II) In urban passenger transport, increasing the attractiveness of "environment-friendly combinations" (foot, bicycle, cart, bus, tram and light rail);

III) In urban goods transport, deliveries by vehicles which are compatible with urban conditions (small goods vehicles with low noise and pollutant emissions), loaded to the correct capacity. In long-distance goods transport, controlled transfer to rail and ship wherever possible. This calls for effective logistical infrastructural measures to optimise the interfacing of short-distance and long-distance transport and the system interchange points between different transport media (e.g. goods traffic centres);

IV) For simply structured transport tasks, as in the case of raw materials projects, special transport systems such as pipelines, light railways, or cableways might be not only more environmentally acceptable but also more economical than lorries, railways or ships.

In highly populated areas, the adverse effects of road transport are directly felt. The rapidly growing cities are already chronically overburdened. As in the industrialised nations, looking realistically at the general conditions, it is impossible to create the infrastructure to cope with the potential demand for private car transport, as this would destroy vital urban functions. Therefore the planning must be geared to needs, favouring categories of traffic which rely on the use of motor vehicles (e.g. urban commercial traffic).

2.4 Administrative, regulatory and financial measures

Administrative, regulatory, and financial measures are also important means of stemming the growth of road traffic and reducing the associated environmental burdens. Some of these have been mentioned in Section 2.1 (petroleum taxes, road tolls, parking restrictions). A more detailed description is given in the environmental brief Traffic and Transport Planning.


3. Notes on the Analysis and Evaluation of Environmental Impacts

Physically measurable limits and standards are available for only certain of the emissions listed under 2.1 and these vary widely even within the industrialised countries. This is because the direct links between traffic emissions, existing overall burdens and the effect of these burdens on people and the environment cannot be precisely described, and may also vary for different risk groups (children, pregnant women etc.). This being so, it is not possible to "calculate" the volume of traffic which will, for example, reach or exceed certain pollutant limits. Fixed limits, as exist in most industrialised nations, are the result of politically negotiated compromises, and are liable to change over time.

It does not therefore seem sensible, within the scope of this brief, to quote the limits which currently apply in, for example, Germany, and which even there are to be regarded as temporary. Moreover, effective monitoring of adherence to limits is highly labour-intensive, and the mere fact of a limit being exceeded does not give any indication as to how emissions may be reduced. Therefore only the titles of those decrees in Germany which impose limits for noise and pollutant emissions are quoted:
- The sixteenth ordinance for the implementation of the Federal Emission Control Act (traffic noise protection decree)
- Memorandum relating to air impurity on roads (MLuS-82) [8]
- Official Journal of the European Communities No. L 36, ECE R 49 (pollutant limit values, [9])

An example of the general trend in determining limits in the industrialised nations is shown in Figure 2, using the example of diesel traffic. Extreme reductions are being demanded, especially in the USA, for soot particles and nitrogen oxides [10].

Fig. 2 - Limits in USA and Europe (from [10])

Therefore, early (qualitative) analysis of all traffic-related projects in order to determine their potential effects is more important than specifying quantitative limits. The investigation may comprise the following stages:

1. An estimate of the potential volume of traffic and its effects to be generated by the project in the widest sense (including an estimate of expected emissions),

2. An investigation into possible ways of reducing traffic and its effects through appropriate technical, economic, legal and political measures, and an assessment of their costs (e.g. construction of by-passes),

3. A reduction in the environmental impact of unavoidable motorised road traffic through appropriate route designs, additional traffic regulations, use of appropriate vehicles (e.g. minibuses during off-peak periods), regular maintenance and inspection of vehicles and through education of transport users to produce conscious avoidance of unnecessary emissions.

4. The assurance of proper methods of disposal of waste oils, lubricants, tyres and scrap, as a condition of supply of vehicles.


4. Interaction with other sectors

This sector directly interacts with road building which, through the routing and grading of highways, is decisive for certain important aspects of the environmental burden imposed by traffic (intersection of unspoilt and developed areas, traffic speed and thus exhaust emissions and accident risks, dangers to groundwater and soil etc.). Conversely, the nature and intensity of the traffic determines the later need for maintenance, development and new construction. Therefore to reduce the environmental impact of traffic, it is essential to achieve harmonisation between the two sectors. Restricting road traffic simply by reducing road capacity (often unintentionally through lack of maintenance), without at the same time improving alternative means of transport, will only lead to higher specific emissions and higher costs to national economies through greater wear and tear on vehicles and roads alike, and lower transport capacity.

The interactions within individual transport systems and with other sectors, dealt with in the environmental brief Transport and Traffic Planning, as applicable to road traffic (see also the summary in Table 1), are briefly as follows:

The road traffic sector is a part of the overall transport system. Environment-oriented transport planning will accordingly seek to find alternative transport concepts (such as combined transport and non-motorised transport). Road traffic overlaps in certain important ways with the tasks of national, regional, and urban planning, because appropriate planning measures on the one hand may reduce the need for road traffic and on the other may minimise its effects from the outset.

As a system which is largely based on petroleum, road traffic accounts for a major part of a country's overall energy consumption; therefore this sector interacts with the energy planning sector.

This sector continually interacts with the promotion of industrial and commercial development, agricultural and forestry projects and extraction of all other natural resources in terms of the potential environmental impact.


5. Summary assessment of environmental relevance

Road traffic is a necessary part of the development and opening up of urban and rural areas. Increased road traffic, which is generally inevitable as infrastructure grows, has far-reaching environmental effects which can only be minimised through extensive efforts in the way of planning, administration (including informing and educating the public) and engineering.

To limit adverse environmental impact effectively, road traffic must be included within an integrated transport plan which adequately takes account of the interactions with other sectors of transport planning, urban planning, and national development planning. When making an overall evaluation of projects, it needs to be borne in mind that the environmental consequences of motorised road traffic are not all bad; in many cases it may also provide a basis for improving living conditions (e.g. through improving supplies of food and medical care) or may be a necessary part of this process (construction of industrial establishments or housing). As with all planning decisions, both the positive and negative effects of road traffic projects need to be weighed up carefully on a case-to-case basis.

In regions where major environmental problems already exist, there is an urgent need for remedial measures to reduce environmental burdens and improve safety. Administrative measures to reduce traffic, raising the training level of mechanics, technicians etc. and proper methods of disposal of pollutants (such as waste oil) will help to achieve this objective. Experience has shown that disposal tasks are best assigned to small commercial enterprises. By contrast, state bodies appear to be more suitable for conducting technical inspections.

In regions where the burdens are currently less severe, the prime task is to conserve the environment. This is essentially a matter of working to prevent undesirable developments through environment-oriented regional development planning and transport and traffic planning.


6. References

[1] BECKMANN: Urban transport planning in development countries

Aspects Schriftenreihe: Forschung, Entwicklung, Planung, Berlin 1987

[2] DIOU: Transports urbains et pays en développement, Transp. Environ. Circ., Vol. 46, 1981.

[3] TOLBA: The World Environment 1972-1982 in: Habitat News, Vol. 1, Nairobi, 1982.

[4] BUNDESAMT FÜR UMWELTSCHUTZ DER SCHWEIZ (Swiss federal environmental protection office): Geschwindigkeitsreduktion und Schadstoffausstoß, Schriftenreihe Umweltschutz, Nr. 22, Bern, 1984.

[5] SEIFRIED: Gute Argumente: Verkehr, Beck'sche Reihe, Munich, 1990.

[6] Was Sie schon immer über Umweltschutz wissen wollten: Ed.: Bundesministerium des Innern (German Federal Ministry of the Interior), Stuttgart, Berlin, Cologne, Mainz, 1980.

[7] Sechzehnte Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes (Verkehrslärmschutzverordnung - 16.BImSchV), Bonn, 1990.

[8] Merkblatt über Luftverunreinigungen an Straßen (MLuS-82): Hrsg.: Forschungsges. für Straßen- und Verkehrswesen, Cologne, 1982.

[9] Official Journal of the European Communities No. L 36, ECE R 49, Brussels.

[10] GEBEL/FLORE/BECKER: Eisenbahn und Umwelt in: Der Nahverkehr, Heft 3/1992, Düsseldorf, 1992.

Further reading:

Der Elsener: Handbuch für Straßen- und Verkehrswesen, Teil M - Straßenbau in Entwicklungsländern, Teil E, 34, Umweltgerechte Straßenplanung, Darmstadt, 1986.

Richtlinien für den Lärmschutz an Straßen (RLS 90): Ed.: Forschungsgesellschaft für Straßen- und Verkehrswesen, Cologne, 1990.

Richtlinien für die Anlage von Straßen (RAS): Teil: Wirtschaftlichkeitsuntersuchungen (RAS-W), Ed.: Forschungsgesellschaft für Straßen- und Verkehrswesen, Cologne, 1986.

SANDLEBEN: Entwicklung eines Bewertungssystems für die Berücksichtigung von Umweltkriterien im Straßenbau, Ed.: Forschungsges. für Straßen- und Verkehrswesen, Schriftenreihe Straßenbau und Straßenverkehrstechnik, Heft 398, Cologne, 1983.

Umweltgerechte Straßenplanung: Seminar des Bundesministers für Verkehr, Ed.: Forschungsges. für Straßen- und Verkehrswesen, Schriftenreihe Straßenbau und Straßenverkehrstechnik, Heft. 352, Cologne, 1981.

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