Future Resilient Transport Networks – Current and Future Impacts of Precipitation on a UK Motorway Corridor by Elizabeth Joanne Hooper A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Geography, Earth and Environmental Sciences College of Life and Environmental Sciences University of Birmingham June 2013 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract This thesis investigates the impact of precipitation on the UK motorway network, with the aim of determining how speed, flow and accidents are affected. Climate change impact assessments require detailed information regarding the impact of weather in the current (baseline) climate and so this thesis seeks to address gaps in knowledge of current precipitation impacts to better inform future climate impact assessments. This thesis demonstrates that whilst precipitation does impact on traffic speeds, there is no universal significant single factor relationship. Indeed, a key threshold is identified at 0 mm hr-1 – the fastest speeds occur when there is no precipitation and speeds immediately decrease at the onset of precipitation. More detailed findings indicate the impact can be detected in both speed and maximum flow across much of the network as well as a downward reduction in the overall speed – flow relationship. In addition to speed flow, the impact of precipitation on road traffic accidents was also investigated. Fifteen percent of accidents in the UK occur in wet weather. Precipitation related accidents are shown to have a prolonged impact on the road network and can continue to cause a decrease in traffic speed and flow for up to three hours afterwards. With increased instances of heavy precipitation predicted as a result of climate change, these findings highlight the subsequent impact on journey speeds, travel times, traffic flows and the associated economic costs. Acknowledgments I would like to thank my supervisors Lee Chapman and Andrew Quinn for their continued support and helping me to see the light at the end of the tunnel when things weren’t going quite as planned. Thank you for all your input and encouragement which helped me make it through to the end. I would also like to thank David Jaroszweski for his help with including the findings of this research in the FUTURENET resilience modelling and the FUTURENET team for their encouragement and suggestions throughout the project. This work was funded by EPSRC ARCC and was part of the FUTURENET project (EP/G060762). I would like to thank the Highways Agency and the IBI Group for providing the HATRIS traffic data, the UKMO (via BADC) for providing the NIMROD precipitation radar data, and the Economic and Social Data Service for providing the STATS19 data. To my family and friends, thank you for all your help and support over the last few years. To Mike especially, thank you for encouraging me to keep going and being there to help me see it through to the end. Contents Chapter 1 – Introduction ....................................................................................................... 1 1.1 Introduction ............................................................................................................ 1 1.2 FUTURENET......................................................................................................... 2 1.3 Aim and Objectives ............................................................................................... 4 1.3.1 Aim .................................................................................................................. 4 1.3.2 Objectives ....................................................................................................... 5 Chapter 2 - Literature Review .............................................................................................. 6 2.1 Introduction ............................................................................................................ 6 2.2 Impacts of Precipitation on the Road Network .................................................... 7 2.3 Extreme Precipitation Events .............................................................................. 10 2.4 Possible Future Impacts of Precipitation on the Road Network ....................... 12 2.4.1 Flooding ........................................................................................................ 14 2.4.2 Journey Times............................................................................................... 16 2.4.3 Maintenance .................................................................................................. 18 2.4.4 Road Safety ................................................................................................... 18 2.4.5 Visibility ....................................................................................................... 19 2.4.6 Embankment Stability .................................................................................. 19 2.5 Existing Studies.................................................................................................... 20 2.6 Summary............................................................................................................... 22 Chapter 3 - Investigating the Impact of Precipitation on Vehicle Speeds on UK Motorways ........................................................................................................................... 24 3.1 Introduction .......................................................................................................... 24 3.2 Background .......................................................................................................... 24 3.3 Method .................................................................................................................. 27 3.3.1 Study Area .................................................................................................... 27 3.3.2 HATRIS Data ............................................................................................... 29 3.3.3 NIMROD Precipitation Radar ..................................................................... 33 3.3.4 GIS Analysis ................................................................................................. 34 3.4 Results and Discussion ........................................................................................ 36 3.4.1 Route Level Analysis ................................................................................... 36 3.4.2 Link Level Analysis ..................................................................................... 46 3.5 Summary............................................................................................................... 50 Chapter 4 - The Impact of Precipitation on Speed – Flow Relationships along a UK Motorway Corridor ............................................................................................................. 52 4.1 Introduction .......................................................................................................... 52 4.2 Impact on Traffic Parameters – Speed and Flow ............................................... 52 4.3 Speed – Flow Relationships and the Speed – Flow Diagram ........................... 56 4.4 Method .................................................................................................................. 58 4.5 Results and Discussion ........................................................................................ 60 4.6 Future Changes..................................................................................................... 70 4.7 Summary............................................................................................................... 77 Chapter 5 - Quantifying the Operational Impact of Traffic Accidents during Precipitation on a Motorway Corridor ............................................................................... 79 5.1 Introduction .......................................................................................................... 79 5.2 Background .......................................................................................................... 80 5.2.1 Precipitation and Road Traffic Accidents ................................................... 80 5.2.2 Climate Change and Road Traffic Accidents ............................................. 85 5.3 Speed and Flow .................................................................................................... 87 5.3.1 Method .......................................................................................................... 87 5.3.2 Results and Discussion................................................................................. 89 5.4 Recovery Times ................................................................................................. 100 5.4.1 Method .......................................................................................................