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Background Information on Traffic Congestion
Media Briefing: Traffic Congestion
1. How does the HA measure congestion?
We have a number of ways of gathering information about conditions on the network. We have a widespread network of automatic traffic count sites to measure traffic volumes. We receive speed data from loops in motorway carriageways - where these are present - and we also receive journey time data through long-term contracts with two major driver information service providers (Trafficmaster and ITIS).
2. What is the HA's definition of congestion?
The traditional congestion indicator used to measure progress is defined as average time lost per vehicle kilometre. This is measured as the difference in travel times along roads between 'free-flow conditions' and the actual average travel times across the day. This definition was chosen because it could be both measured (at a network-wide level of aggregation) and forecast into the future, and because it was thought to represent the impacts of congestion that mattered most to business.
Although this measure continues to be useful for many purposes, especially investment prioritisation, it cannot be easily translated to motorists' experience of driving, and does not measure reliability of journeys. We are working with DfT to develop additional indicators to address these concerns, and new congestion targets will be published by July 2005.
Journey time data collected by the Agency can be presented in map form, and provides a high-level indication of where congestion may be a problem. Detailed link-by-link data underpinning the maps are circulated to our Area teams to assist with scheme identification.
Using the traditional measure of congestion, the busiest motorways have been the western side of the M25, and M6 junctions 10-6 into Birmingham. The opening of the M6 Toll has relieved the latter significantly, such that congestion is now not as great as on the M25.
More information about the relative performance of routes will become available next year. The White Paper Future of Transport announced that congestion ratings would be published for key routes reflecting their performance against new indicators, as part of the commitment to publish new targets by July 2005.
3. Is it possible that the whole of the motorway system could ever lock solid?
This has never happened, and improvements in travel information, and strategic management through the Traffic Control Centre, make it less likely to happen in the future.
To help motorists plan their journeys the HA has recently introduced a Traffic Forecaster page on its website (www.highways.gov.uk/trafficinfo). It enables motorists to select a travel date and time in the future and to see likely average speeds based on the experience of similar days in the past year.
Past research suggests that about 25% of all congestion is caused by unpredictable events (e.g. accidents and the weather), and up to 15% by roadworks. The remainder is the result of regular "weight of traffic" - commuting in the peak - and often referred to as recurrent congestion. Based on that research perhaps 40% of congestion is capable of being influenced by a combination of better roadwork and incident management. These are the areas on which the HA will be concentrating in the coming years, in addition to a targeted programme of improvements designed to relieve some of the worst locations for recurrent congestion.
Innovative traffic management, the deployment of traffic officers, influencing travel behaviour, targeted capital investment and improved travel information can all have a significant impact on congestion levels.
