Improving Journey Time Reliability

The Highways Agency has been set a PSA target to reduce average vehicle delay for the 10% worst journeys on each of its routes. At a time when traffic volumes are continuing to grow, this is highly challenging and the Agency has been trialling a number of initiatives, such as Active Traffic Management, to minimise the risk of delays. To help determine how much of an effect these initiatives are having and the extent to which continuing traffic growth is counteracting the improvements, the HA has appointed a team led by Risk Solutions to investigate the problem.

The project team includes experts from ITS Leeds University, WSP Group and Parsons Brinckerhoff, and the work is being tackled in two complementary workstreams. The first workstream is developing a better understanding of the relationship between traffic growth and journey time reliability through detailed analysis of data for a sample of HA roads. This will then be used to assess the impact of traffic growth on the Agency’s performance against the PSA target. Workstream 2 is then developing a better understanding of the relationship between journey times and a number of factors, including traffic growth, through the construction of a high-level model of the relationships. This will take account of the latest research in this area.

Outputs from the project will be:

  • An assessment of factors influencing the PSA target and the Agency’s performance against this target
  • A prototype 'Network Performance Model' capable of modelling the effects of traffic growth and intervention measures on journey time reliability
  • Recommendations for how the work could be taken forward into the future.