Assessing the Impact of Planned Road Works and Street Works in London
J McNuff, Transport for London, UK; J Polak, Imperial College London, UK
The objective of this paper is to present the results of a study that has developed a new methodology to characterise the causal relationship between planned works and network performance in London.
Increasingly, Traffic Authorities are concerned with the monitoring of network performance for reporting purposes. Simultaneously, there is great pressure on both highway authorities and statutory undertakers to maintain and improve the networks for which they are responsible. As a result, essential works on behalf of either are commonplace, particularly in urban areas such as London. These works are recognised as having a detrimental affect on network performance and are a highly visible intervention of great significance to road users. Co-ordination and management of road works and street works is therefore a key component of successful network management. This is reflected by the steady introduction of sections of the Traffic Management Act 2004 in the UK ? most recently in January 2009 with the introduction of a London Permit Scheme, which places tighter controls on the timing and duration of works, and makes it a criminal offence to breach conditions of any works permit granted.
Notwithstanding the practical importance of the subject, the formal study of the impact of planned works in urban areas such as London has to date been limited. Much of the existing literature in the area has either focused on interurban contexts or has been concerned principally with investigating the properties of alternative network performance measures themselves, rather than the impact of planned works. An improved understanding of the affect of works on network performance, and more specifically a methodology for assessing the magnitude of the likely impact of planned works is desirable as it would allow:
? The potential impact of works on network performance to be objectively assessed;
? Determination of the configurations or timings of the works that are likely be least disruptive;
? Improved information provided to the users of the network about likely delays and suggested alternative routes; and
? A mechanism for identifying accountability for network performance issues related to works.
Against this background, the objective of this paper is to present the results of a study that has developed a new methodology to characterise the causal relationship between planned works and network performance in London. This methodology is based on the statistical analysis of an extensive dataset consisting of information on (i) works-specific factors such as the length of the works site, the location of the works site with respect to adjacent junctions, and the proportion of (lateral) carriageway space occupied by the works and (ii) traffic data including the flow and travel time on affected links.
The paper comprises a number of sections. In the first section, the general policy background is discussed and the growing prominence of works-related network interventions in London is highlighted. The second section presents a brief overview of the relevant academic literature, highlighting a number of critical gaps in relation to understanding of works-related impacts in urban areas and discussing some of the methodological challenges entailed, including the definition of appropriate measures of network performance. The third section summarises the study methodology concentrating both on how the effect of planned works on capacity (and hence performance) is represented in the analysis and on the statistical issues associated with the analysis of a complex time series dataset. The fourth section describes the data used in the study: Based on a systematic site selection process that considered the availability of journey time, traffic flow and works data, 16 works scenarios were identified. The fifth section presents the results of the statistical analysis of these data. The results indicate that traffic flow, works site length, and distance from the works site to adjacent junctions are significant factors influencing network performance. The final section discusses the practical implications of the results for the co-ordination and management of road works and street works.
Association for European Transport