Stephen Ison

Road Traffic Congestion and Crash Severity: Econometric Analysis Using Ordered Response Models

There is an ongoing debate among transport planners and safety policy makers as to whether there is any association between the level of traffic congestion and road safety. One can expect that the increased level of traffic congestion aids road safety and this is because average traffic speed is relatively low in a congested condition relative to an uncongested condition, which may result in less severe crashes. The relationship between congestion and safety may not be so straightforward, however, as there are a number of other factors such as traffic flow, driver characteristics, road geometry, and vehicle design affecting crash severity. Previous studies have employed count data models (either Poisson or negative binomials and their extensions) while developing a relationship between the frequency of traffic crashes and traffic flow or density (as a proxy for traffic congestion). The use of aggregated crash counts at a road segment level or at an area level with the proxy for congestion may obscure the actual relationship. The objective of this study is to explore the relationship between the severity of road crashes and the level of traffic congestion using disaggregated crash records and a measure of traffic congestion while controlling for other contributory factors. Ordered response models such as ordered logit models, heterogeneous choice models, and generalized ordered logit (partially constrained) models suitable for both ordinal dependent variables and disaggregate crash data are used. Data on crashes, traffic characteristics (e.g., congestion, flow, and speed), and road geometry (e.g., curvature and gradient) were collected from the M25 London orbital motorway between 2003 and 2006. Our results suggest that the level of traffic congestion does not affect the severity of road crashes on the M25 motorway. The impact of traffic flow on the severity of crashes, however, shows an interesting result. All other factors included in the models also provide results consistent with existing studies.

Impact of traffic congestion on road accidents: a spatial analysis of the M25 motorway in England

Traffic congestion and road accidents are two external costs of transport and the reduction of their impacts is often one of the primary objectives for transport policy makers. The relationship between traffic congestion and road accidents however is not apparent and less studied. It is speculated that there may be an inverse relationship between traffic congestion and road accidents, and as such this poses a potential dilemma for transport policy makers. This study aims to explore the impact of traffic congestion on the frequency of road accidents using a spatial analysis approach, while controlling for other relevant factors that may affect road accidents. The M25 London orbital motorway, divided into 70 segments, was chosen to conduct this study and relevant data on road accidents, traffic and road characteristics were collected. A robust technique has been developed to map M25 accidents onto its segments. Since existing studies have often used a proxy to measure the level of congestion, this study has employed a precise congestion measurement. A series of Poisson based non-spatial (such as Poisson-lognormal and Poisson-gamma) and spatial (Poisson-lognormal with conditional autoregressive priors) models have been used to account for the effects of both heterogeneity and spatial correlation. The results suggest that traffic congestion has little or no impact on the frequency of road accidents on the M25 motorway. All other relevant factors have provided results consistent with existing studies.

Airports' perspectives on the growth of low-cost airlines and the remodeling of the airport-airline relationship.

Abstract This paper explores the way in which airports have responded to the apparent opportunities afforded them by the growth of low-cost airlines. The adoption of a so-called low-cost model by airlines has made many airports fundamentally reconsider who their customers are. The low-cost model impels airlines to negotiate contracts which significantly reduce aeronautical charges by the airport, consequently seeking to make up this short fall by commercial revenues from the increased passenger numbers. This is not however without consequences for the airports, their passengers and the relationship between the airport and its existing airline operators. The recent growth of low-cost airlines has naturally attracted the attention of airport managers as a source of volume to alleviate commercial pressures; however, due to low-cost airlines’ unwillingness to pay high airport fees there is the difficulty of translating any increased volume of passengers into increased revenue. This paper reviews the behaviour of a number of different airports in Europe and identifies important issues for airport management to consider when negotiating with low-cost airlines.

Implementing road user charging: the lessons learnt from Hong Kong, Cambridge and Central London.

Road user charging has long been advocated as a means of dealing with congestion in urban areas. Numerous schemes have been proposed but have advanced little beyond the drawing board. This paper draws on the experiences of two such road user charging schemes, namely Electronic Road Pricing in Hong Kong, China, and Congestion Metering in the city of Cambridge, UK, and it seeks to make comparisons with the way implementation of congestion charging in Central London, UK, has been undertaken. What lessons can be learnt from the three examples that would aid authorities considering such a course of action? Certain issues have contributed to the two schemes not being implemented, such as the level of congestion not being severe enough, the clarity of objectives, invasion of road user’s privacy, and timing and presentation. The paper seeks to compare and contrast the issues resulting in the schemes not being implemented with those of the successfully implemented scheme. The conclusion is that it is not possible to attribute the successful implementation of congestion charging to one issue alone. The role of a policy champion, public support given the severity of congestion, a single implementing agency, an understanding of the scheme’s objectives, and timing and clear presentation have all been important factors.

Predicting accident frequency at their severity levels and its application in site ranking using a two-stage mixed multivariate model

Accident prediction models (APMs) have been extensively used in site ranking with the objective of identifying accident hotspots. Previously this has been achieved by using a univariate count data or a multivariate count data model (e.g. multivariate Poisson-lognormal) for modelling the number of accidents at different severity levels simultaneously. This paper proposes an alternative method to estimate accident frequency at different severity levels, namely the two-stage mixed multivariate model which combines both accident frequency and severity models. The accident, traffic and road characteristics data from the M25 motorway and surrounding major roads in England have been collected to demonstrate the use of the two-stage model. A Bayesian spatial model and a mixed logit model have been employed at each stage for accident frequency and severity analysis respectively, and the results combined to produce estimation of the number of accidents at different severity levels. Based on the results from the two-stage model, the accident hotspots on the M25 and surround have been identified. The ranking result using the two-stage model has also been compared with other ranking methods, such as the naïve ranking method, multivariate Poisson-lognormal and fixed proportion method. Compared to the traditional frequency based analysis, the two-stage model has the advantage in that it utilises more detailed individual accident level data and is able to predict low frequency accidents (such as fatal accidents). Therefore, the two-stage mixed multivariate model is a promising tool in predicting accident frequency according to their severity levels and site ranking.

The Implementation and Effectiveness of Transport Demand Management Measures : An International Perspective

Contents: Introduction: TDM measures and their implementation, Stephen Ison and Tom Rye Purchase, circulation and fuel taxation, Stephen Potter Road user charging, Kenneth Button and Henry Vega The role of intelligent transport systems (ITS) in implementing road pricing for congestion management, David Gillen The land use and local economic impacts of congestion charging, David Banister Tradable driving rights in urban areas: their potential for tackling congestion and traffic-related pollution, Charles Raux The politics and economics of parking on campus, Donald Shoup A view of parking policy in an Australian city, William Young Park and ride, Stuart Meek Public transport subsidisation, John Preston The substitution of communications for travel?, Glenn Lyons, Sendy Farag and Hebba Haddad Travel plans, Marcus Enoch and Lian Zhang Index.

A Fiasco of Volcanic Proportions? Eyjafjallajokull and the Closure of European Airspace

Abstract The unprecedented and recurrent closure of much of UK and northern European airspace from 14 April 2010, following the eruption of Iceland’s Eyjafjallajökull volcano, caused the cancellation of 108,000 flights, disrupted the travel plans of 10.5 million passengers, and cost the airline industry in excess of

Bridging the skills gap: a regionally driven strategy for resolving the construction labour market crisis

1.7 billion in lost revenue. The airspace closures highlighted the inherent riskiness of aviation and destabilised dominant cultural discourses of the ‘superiority’ and capability of aviation technology. It also brought issues of risk acceptability and our socio‐economic reliance on air travel into sharp relief. This paper explores how the political and media framing of the response to the airspace closures as a human ‘policy fiasco’ served to obfuscate the inherent dangers of aviation and ‘get Europe flying’ again. Thus, this paper contends that this particular fiasco was ‘necessary’ in that it served to highlight the fragility of air travel and the vulnerabilities of the mobile citizen.

The construction labour market skills crisis: the perspective of small-medium-sized firms

Econometric forecasts indicate that the UK construction industry faces a severe skills deficit in the foreseeable future. This paper details the results of a major labour market research projects, which canvassed the opinions of over 50 industry stakeholders within the East Midlands region of the UK. Focus groups were used to elicit the collective opinions of key clients, consultants, contractors, industry bodies and employers of all sizes. The key themes and requirements discussed by the participants are used to develop a conjoined strategy for bridging the industrys skills gap at a regional level. It is argued that this package of mutually supportive measures could provide a transferable strategy for addressing skills deficiencies in other regions, particularly given the espoused government aspiration to devolve labour market planning activities to provincial forums and regional development agencies.

A spatio-temporal analysis of the impact of congestion on traffic safety on major roads in the UK

Reports abound of the detrimental effect of the construction skills crisis on the performance and future development of the UK construction industry. The industrys continued growth in output, coupled with its unpopularity as a career choice, has led to extreme pressure on its labour market capacity. There remains, however, a paucity of empirical research into the nature of its highly complex labour market. In particular, very little attention has been paid to the impacts being felt by the smaller firms who account for the vast majority of the industrys economic output and employment. This paper reports on research that has explored the perspectives of smaller employers with respect to the skills crisis. Using an inductive methodology, this research canvassed the opinions of representatives of small‐ and medium‐sized (SME) firms in order to establish the impact of skills shortages on the operational efficiency of the industry. The paper reveals the complex interplay of factors which have combined to shape the industrys skills crisis in recent years and uncovers the practical implications for firms attempting to operate in increasingly tight labour market conditions.