Urban and rural networks
- Designing for road function
- Designing to keep injury severity low
- Road classification
- Self explaining roads
Urban and rural networks
Although the same general functional management principles need to be applied for both urban and rural road networks, the detailed functions that need to be served differ, and the mix of traffic differs. Thus the way in which each function is translated into design also differs.
Factors that need to be taken into account in urban areas include
- High density both of traffic and of other functions being served by the road
- Integration of traffic into residential space
- Catering for the needs of a wide range of road users using different modes
Accidents in residential areas are characterised by larger proportions of accidents involving children and the elderly and accident locations scattered widely rather than concentrated at black spots . The majority of the accidents are likely to occur on roads that serve a distributive function within these areas, and the road layout plays an important part in the intensity of accident risk, with absolute number of accidents being higher in older layouts
Area-wide measures are therefore necessary for the design and implementation of countermeasures. Measures must not only address accident reduction, but should also take into account in resident's satisfaction with the area within which they are living. Early involvement of the community in the decision making process is important if this is to be achieved.
Planning principles for new residential areas should, where possible, include
- Differentiation of streets according to their function
- Distribution of traffic into a residential area from a ring road rather than central distribution
- Cul-de-sac streets or short lengths divided by speed reducing measures
- Housing which accesses onto the access streets rather than the distributor streets
Although such layouts cannot be applied in full to the modification of existing street patterns, the same principles are equally applicable.
Urban Safety Management in UK
Principles adopted for effective urban safety management in UK include
- Consider all kinds of road user especially the most vulnerable
- Consider the functions and use of different kinds of road
- Formulate a safety strategy for the area as a whole
- Integrate existing accident reduction efforts into the safety strategy
- Relate safety objectives to other objectives for the urban area
- Encourage all professional groups to help achieve safety objectives
- Guard against adverse effects of other programmes upon safety
- Use the scarce expertise of road safety professionals effectively
- Translate strategy and objectives into local area safety schemes
- Monitor progress towards safety objectives
Four steps in defining functions and objectives are
- Identify current road hierarchy
- Appraise extent and characteristics of accidents and public perception of safety on all parts of the network
- Assess traffic flow and performance on each route in relation to the functions expected from its role in the hierarchy
- Set safety objectives for each part of the road network
Source: IHT (1990b), Department for Transport (2003)
The wide range of social and environmental objectives leading to improvement of urban areas means that integrated traffic safety management is important . In addition to playing a leading role where traffic safety is the primary stimulus for a scheme, traffic safety experts need also to seek opportunities to improve safety where other objectives provide the main basis for change. The emergence of good integrated schemes is usually heavily dependent on significant national or regional involvement, or on strong local political will.
Urban safety management programmes are expensive and involve engineering works over a large area. Good co-ordination and management and extensive involvement of local representatives are therefore essential to successful implementation .
The European Commission DUMAS project
The DUMAS project was established with partners from 9 European countries to encourage the wider use of urban safety management principles. The DUMAS Design Framework defines potential interactions in order to make urban designers, planners and engineers more aware of the effect of their strategies on others. A joint vision for the urban area and strong political leadership are required. Examples are provided of the management structures that might be developed and the consultation processes likely to be necessary. The key principles of managing traffic to achieve a safer distribution, and managing speed to achieve a safer circulation emphasise the need for a clear functional hierarchy linked to a speed management strategy for the whole urban area.
Source: European Commission, 2001; Department for Transport, 2003
A network of higher quality interurban roads is required in every country to ensure the safe and efficient transit of people and goods. Part of this network is usually provided by motorway standard roads, supplemented by other divided, restricted access roads (called express roads in some countries). The standard of this latter group varies between and within countries. High interurban flows are also carried on 2 lane roads in some countries, although these are more suited to local rural roads.
Average fatal accident rates per vehicle km can be up to six times higher on 2 lane rural roads than on motorways, and decrease as traffic flows increase . The density of severe (fatal and serious injury) accidents per km is typically greatest for divided carriageways below motorway standard, but less than twice that on motorways or 2 lane roads.
Eighty per cent of all fatal accidents on major interurban roads occur due to single vehicles leaving the road, impacts at junctions, head-on impacts with opposing vehicles or impacts involving vulnerable road users .
The proportion within each of the four groups varies between countries depending on the characteristics of their road network and the traffic flow levels. The proportion also varies between road types, and at different flow levels .
The European Union has published guidelines for the design and management of the Trans European Network, and is currently consulting on an infrastructure Directive. Several European research projects  have developed advice on design standards for interurban rural roads.