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Urban Road User Charging Online Knowledge Base
What The Research Gaps?Whilst road user charging is founded upon the notion of reducing congestion, there is no accepted definition of what a “reasonable” level of congestion is and how congestion should best be measured. Optimal congestion does not mean the total removal of congestion from the network as this would imply always supplying costly excess capacity. As we have noted earlier, TfL’s preferred measure of congestion is in terms of excess travel time over free flow conditions. One drawback of this measure is that reductions in excess delay can be a combination of reductions in actual delay experienced and increases in travel time under free flow conditions. Further research could usefully examine whether more robust measures of congestion are justified.
It is often assumed that the changes in the traffic can be deduced by comparing the before and after scenario or by monitoring the changes year on year. In either case, it is impossible to disentangle the effects of measures that are not part of the congestion charging scheme from exogenous factors. Ideally, we would like to compare what happened with and without the scheme in a real world setting but this is impossible in reality, Thus an interesting unexplored question is the development of a robust baseline which can then be used as a proxy for the “without charging situation”.
The traffic impacts examined across three different countries suggest that traffic impacts of road user charging are relatively similar. However local situation-specific factors will differ and this is an important area for further research.
No information on this theme is currently available from the case studies
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