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  • Journal article
    Li H, Graham DJ, 2016,

    The Heterogeneous Treatment Effects of Speed Cameras on Road Safety

    , Accident Analysis & Prevention, Vol: 97, Pages: 153-161, ISSN: 0001-4575

    This paper analyses how the effects of fixed speed cameras on road casualties vary across sites with different characteristics and evaluates the criteria for selecting camera sites. A total of 771 camera sites and 4787 potential control sites are observed for a period of 9 years across England. Site characteristics such as road class, crash history and site length are combined into a single index, referred to as a propensity score. We first estimate the average effect at each camera site using propensity score matching. The effects are then estimated as a function of propensity scores using local polynomial regression. The results show that the reduction in personal injury collisions ranges from 10% to 40% whilst the average effect is 25.9%, indicating that the effects of speed cameras are not uniform across camera sites and are dependent on site characteristics, as measured by propensity scores. We further evaluate the criteria for selecting camera sites in the UK by comparing the effects at camera sites meeting and not meeting the criteria. The results show that camera sites which meet the criteria perform better in reducing casualties, implying the current site selection criteria are rational.
  • Journal article
    Cohen JM, Barron AS, Anderson RJ, Graham DJet al., 2016,

    Impacts of Unattended Train Operations (UTO) on Productivity and Efficiency in Metropolitan Railways

    , Transportation Research Record-Series, Vol: 2534, Pages: 75-83, ISSN: 0361-1981

    Urban metro subway systems (metros) around the world are choosing increasing levels of automation for new and existing lines: the global length of metro lines capable of unattended train operation (UTO) is predicted to triple in the next 10 years. Despite significant investment in this technology, empirical evidence for the financial and service quality impacts of UTO in metros remains scarce. This study used questionnaires and semistructured interviews with the Community of Metros and Nova Group benchmarking groups to assemble emerging evidence of how automation affected costs, staffing, service capacity, and reliability. The results from an analysis of data from 23 lines suggested that UTO could reduce staff numbers by 30% to 70%, with the amount of wage cost reduction depending on whether staff on UTO lines were paid more. On the basis of the experience of seven metros, the capital costs of lines capable of UTO were higher, but the internal rate of return had been estimated by two metros at 10% to 15%. Automated lines were capable of operating at the highest service frequencies of up to 42 trains per hour, and the limited available data suggested that automated lines were more reliable. The findings indicated that UTO was a means to a more flexible and reliable operating model that could increase metro productivity and efficiency. The study identified important work needed to understand the impacts of UTO and identify where statistical analyses would add value once sufficiently large data sets became available.
  • Journal article
    Canavan S, Graham D, Melo P, Anderson R, Barron A, Cohen Jet al., 2016,

    The Impacts of Moving Block Signalling on Technical Efficiency: An Application of Propensity Score Matching on Urban Metro Rail Systems

    , Transportation Research Record, Vol: 2534, Pages: 68-74, ISSN: 0361-1981

    This study tested the effect of introducing moving-block signaling on the technical efficiency of urban metro rail systems. The study used a panel data set of 27 urban metro systems across 20 countries for 2004 to 2012. When moving-block signaling was considered as a treatment, the effect of the associated benefits on output efficiency levels was able to be measured. Stochastic frontier analysis was employed to estimate technical efficiencies for each metro, and then propensity score matching was applied to evaluate the effect of the type of signaling on technical efficiency. The study allowed the selection of appropriate reference groups and accounted for confounding factors. The study is novel in its provision of empirical evidence of this nature. The results indicate that the technical efficiency of a metro can be improved by 11.5%.
  • Conference paper
    Yannis G, Dragomanovits A, Laiou A, Richter T, Ruhl S, La Torre F, Domenichini L, Graham D, Karathodorou N, Li Het al., 2016,

    Use of Accident Prediction Models in Road Safety Management – An International Inquiry

    , 6th Transport Research Arena, Publisher: Elsevier BV, Pages: 4257-4266, ISSN: 2352-1465
  • Journal article
    Graham DJ, Li H, 2016,

    Quantifying the causal effects of 20 mph zones on road casualties in London via doubly robust estimation

    , Accident Analysis & Prevention, Vol: 93, Pages: 65-74, ISSN: 0001-4575

    This paper estimates the causal effect of 20 mph zones on road casualties in London. Potential confounders in the key relationship of interest are included within outcome regression and propensity score models, and the models are then combined to form a doubly robust estimator. A total of 234 treated zones and 2844 potential control zones are included in the data sample. The propensity score model is used to select a viable control group which has common support in the covariate distributions. We compare the doubly robust estimates with those obtained using three other methods: inverse probability weighting, regression adjustment, and propensity score matching. The results indicate that 20 mph zones have had a significant causal impact on road casualty reduction in both absolute and proportional terms.
  • Conference paper
    Achurra Gonzalez PE, Angeloudis P, Zavitsas K, Niknejad SA, Graham DJet al., 2016,

    Attacker-defender modelling of transport vulnerability in maritime logistics corridors

    , 2nd International Workshop on Maritime Flows and Networks
  • Conference paper
    Horcher D, Graham DJ, 2016,

    Crowding and the marginal cost of travelling under second-best capacity provision

    , International Transport Economics Association Annual Conference

    The classic economic theory of capacity optimisation in public transport suggests that the welfare maximising frequency and vehicle size increase with demand, and therefore the optimal occupancy rate may not dependent on demand; crowding can be internalised through capacity adjustment. On the other hand, empirical studies show that the crowding externality does contribute significantly to the social cost of public transport usage in large metropolitan areas. This paper presents a theoretical framework that explains why rational second-best capacity provision may lead to a wide range of demand dependent crowding levels under economies of vehicle size, infrastructure constraints and demand fluctuations. We derive the marginal external waiting time, crowding and operational costs of travelling for second-best scenarios, and explore the resulting subsidy rates. Thus, we take an important step towards the full understanding of optimal demand and crowding dependent pricing in public transport.
  • Journal article
    Graham DJ, McCoy EJ, Stephens DA, 2016,

    Approximate Bayesian inference for doubly robust estimation

    , Bayesian Analysis, Vol: 11, Pages: 47-69, ISSN: 1931-6690

    Doubly robust estimators are typically constructed by combining outcome regression and propensity score models to satisfy moment restrictions that ensure consistent estimation of causal quantities provided at least one of the component models is correctly specified. Standard Bayesian methods are difficult to apply because restricted moment models do not imply fully specified likelihood functions. This paper proposes a Bayesian bootstrap approach to derive approximate posterior predictive distributions that are doubly robust for estimation of causal quantities. Simulations show that the approach performs well under various sources of misspecification of the outcome regression or propensity score models. The estimator is applied in a case study of the effect of area deprivation on the incidence of child pedestrian casualties in British cities.
  • Report
    Horcher D, Graham DJ, Anderson RJ, 2016,

    Merging smart card data and train movement data: How to assign trips to trains?

    , Merging smart card data and train movement data: How to assign trips to trains?

    This report explains the assignment method applied to link trips compiled in smart card data to train movements recorded in the signalling system. Particular attention has been paid to (1) origin-destination pairs with multiple potential route options, (2) peak-hour trips delayed by di culties in boarding crowded trains at the origin station, and (3) trips originating or ending on rail lines not included in the train movement dataset.In the current version of this paper the metro network on which the method has been applied is anonymised.
  • Journal article
    Melo PC, Graham DJ, Levinson D, Aarabi Set al., 2016,

    Agglomeration, accessibility and productivity: evidence for large metropolitan areas in the US

    , Urban Studies, Vol: 54, Pages: 179-195, ISSN: 1360-063X

    This paper estimates the productivity gains from agglomeration economies for a sample of the largest metropolitan areas in the United States using measures of urban agglomeration based on employment density and employment accessibility. The latter is a more accurate measure of economic proximity and allows testing for the spatial decay of agglomeration effects with increasing travel time. We find that the productivity gains from urban agglomeration are consistent between measures, with elasticity values between 0.07 and 0.10. The large majority of the productivity gains occur within the first 20 minutes, and do not appear to exhibit significant nonlinearities.
  • Conference paper
    La Torre F, Domenichini L, Meocci M, Graham D, Karathodorou N, Richter T, Ruhl S, Yannis G, Dragomanovits A, Laiou Aet al., 2016,

    Development of a transnational accident prediction model

    , 6th Transport Research Arena (TRA), Publisher: ELSEVIER SCIENCE BV, Pages: 1772-1781, ISSN: 2352-1465
  • Conference paper
    Horcher D, Graham DJ, 2015,

    The dark side of travel passes: Wrong incentive in crowding

    , Transportation Research Board 95th Annual Meeting, Washington D.C.
  • Conference paper
    Horcher D, Graham DJ, Anderson R, 2015,

    The link between crowding pricing and seat supply in public transport

    , Transportation Research Board 95th Annual Meeting, Washington D.C.
  • Journal article
    Brage-Ardao R, graham DJ, anderson RJ, 2015,

    Determinants of Rolling Stock Maintenance Cost in Metros

    , Proceedings of the Institution of Mechanical Engineers Part F -Journal of Rail and Rapid Transit, Vol: 230, Pages: 1487-1495, ISSN: 0954-4097

    This study examines the economies of scale and the determinants of rolling stock maintenance costs for 24 urban rail transit operators. The estimates reveal significant returns to scale in maintenance for both per car and per car kilometre. The econometric analysis also provides statistically significant cost elasticities for wages and staff hours, suggesting substitution effects between factors. Staff outsourcing is found to significantly decrease costs, whereas higher levels of fleet availability at the peak and rolling stock failures increase it. The effect of the age of rolling stock and the network is negligible on rolling stock maintenance costs; however, the analysis reveals a downward trend in rolling stock costs among the metros in the CoMET and Nova consortia.
  • Journal article
    Mohammad SI, Graham DJ, Melo PC, 2015,

    The effect of the Dubai metro on the value of residential and commercial properties

    , Journal of Transport and Land Use, Vol: 10, Pages: 263-290, ISSN: 1938-7849

    This paper analyzes the impact of the newly operated Dubai Metro on the sale transaction value of dwellings and commercial properties. The effect is estimated for properties within different catchment zones of a metro station using difference-in-differences and hedonic pricing methods on both repeated cross-sectional data and pseudo panel data. Our estimates show a positive effect of the metro on sale values of both residential and commercial properties, although the effect is stronger for commercial properties. The models also reveal that the effect of the metro on the value of dwellings and commercial properties is largest within 701 to 900 meters of a metro station and is about 13 percent and 76 percent, respectively.
  • Conference paper
    Cohen JM, Parasram R, Anderson R, Barron Aet al., 2015,

    Global trends in metro station organisation and management

    , 43rd European Transport Conference

    Increased uptake of smart ticketing, mass availability of personal information technology,and roll-out of 4G and WiFi coverage within metropolitan railway systems, are leadingmetros to change the way they manage stations.
  • Conference paper
    Cohen JM, Barron A, Anderson R, Graham Det al., 2015,

    Increased likelihood of injury as a form of transport disadvantage for differently abled and elderly travellers: Evidence from urban metro subway systems

    , 14th International Conference on Mobility and Transport for Elderly and Disabled Persons
  • Conference paper
    Anderson RJ, Brage-Ardao R, Graham DJ, barron Aet al., 2015,

    Econometric Benchmarking of Metro Operating Costs. Methods and Applications

    , European Transport Conference 2015
  • Journal article
    Brage-Ardao R, graham DJ, Anderson RJ, 2015,

    Determinants of Train Service Costs in Metro Operations

    , Transportation Research Board 94th Annual Meeting
  • Journal article
    McCoy EJ, Graham DJ, Stephens DA, 2014,

    Quantifying causal effects of road network capacity expansions on traffic volume and density via a mixed model propensity score estimator

    , Journal of the American Statistical Association, Vol: 109, ISSN: 1537-274X

    Road network capacity expansions are frequently proposed as solutions to ur-ban traffic congestion but are controversial because it is thought that theycan directly ‘induce’ growth in traffic volumes. This paper quantifies causaleffects of road network capacity expansions on aggregate urban traffic volumeand density in US cities using a mixed model propensity score (PS) estimator.The motivation for this approach is that we seek to estimate a dose-responserelationship between capacity and volume but suspect confounding from bothobserved and unobserved characteristics. Analytical results and simulationsshow that a longitudinal mixed model PS approach can be used to adjust ef-fectively for time-invariant unobserved confounding via random effects. Ourempirical results indicate that network capacity expansions can cause substan-tial increases in aggregate urban traffic volumes such that even major capacityincreases can actually lead to little or no reduction in network traffic densi-ties. This result has important implications for optimal urban transportationstrategies.
  • Journal article
    Li H, Graham DJ, Majumdar A, 2014,

    Effects of changes in road network characteristics on road casualties: An application of full Bayes models using panel data

    , Safety Science, Vol: 72, Pages: 283-292, ISSN: 0925-7535

    In order to ensure a high level of road safety, road network planning needs to be based on the best knowledge available of the effects of road design on road safety. In this study, we look into how changes in road network characteristics affect road casualties. An approach based on traffic assignment is proposed in order to estimate the traffic exposure at ward level. We apply a widely used approach for before–after evaluation studies, the Bayesian method. We also use a panel semi-parametric model to estimate the dose–response function for continuous treatment variables. The result suggests that there are more casualties in areas with better connectivity and accessibility, where more attention should be paid to safety countermeasures.
  • Report
    Cohen JM, Barron AS, Anderson RJ, 2014,

    Human Operational Support on UTO Lines

    , Publisher: Imperial College London

    Metro automation is an increasing trend worldwide. This study investigated the realities of operating automated lines, focused on the following key questions: What staffing levels are used by metros, and what are the pros and consof each approach? Under what circumstances do metros choose to staff all trains on linesthat are capable of unattended operations? What technology is required to enable automated operations? Do the benefits of automation outweigh the additional investment?
  • Book chapter
    Graham D, Hebbert M, 2014,

    London

    , Metropolitan Planning in Britain: A Comparative Study, Pages: 63-77
  • Journal article
    Ramli AR, Graham DJ, 2013,

    The demand for road transport diesel fuel in the UK: Empirical evidence from static and dynamic cointegration techniques

    , Transportation Research Part D - Transport and Environment, Vol: 26, Pages: 60-66, ISSN: 1361-9209
  • Journal article
    Li H, Graham DJ, Majumdar A, 2013,

    The impacts of speed cameras on road accidents: An application of propensity score matching methods

    , ACCIDENT ANALYSIS AND PREVENTION, Vol: 60, Pages: 148-157, ISSN: 0001-4575
  • Journal article
    Anderson R, Condry B, Findlay N, Brage-Ardao R, Li H, Condry B, Findlay N, Brage-Ardao R, Li Het al.,

    Measuring and Valuing Convenience and Service Quality: A Review of Global Practices and Challenges from Mass Transit Operators and Railway Industries

    , International Transport Forum Discussion Papers, No. 2013/16, PCED Publishing, Paris, ISSN: 2223-439X
  • Journal article
    Melo PC, Graham DJ, Brage-Ardao R, 2013,

    The productivity of transport infrastructure investment: A meta-analysis of empirical evidence

    , REGIONAL SCIENCE AND URBAN ECONOMICS, Vol: 43, Pages: 695-706, ISSN: 0166-0462
  • Journal article
    Mare DC, Graham DJ, 2013,

    Agglomeration elasticities and firm heterogeneity

    , Journal of Urban Economics, Vol: 75, Pages: 44-56

    This paper examines three key issues encountered when estimating the relationship between agglomeration and multi factor productivity (‘agglomeration elasticities’): the sorting of heterogeneous firms, the convexity of agglomeration effects, and the challenges of identifying the impact of persistent spatial differences in effective density. We use a firm-level panel containing production data together with detailed information on the geographic location of employment, covering a high proportion of the New Zealand economy. We are able to control for heterogeneity along firm, region, and industry dimensions, and to estimate separate agglomeration elasticities across industries and regions. Sorting leads to upward biased elasticity estimates but using firm fixed effects can lead to downward bias due to the highly persistent nature of agglomeration variables. Our preferred estimates control for sorting across regions and industries. Overall, we find a positive agglomeration elasticity of 0.066. Within industries and, to a lesser extent within regions, there is pronounced variation in the strength of agglomeration effects, and evidence of decreasing returns to agglomeration. High density areas attract firms that benefit most from agglomeration.
  • Journal article
    Barron A, Melo PC, Cohen JM, Anderson RJet al., 2013,

    Passenger-Focused Management Approach to Measurement of Train Delay Impacts

    , Transportation Research Record, Vol: 2351, Pages: 46-53, ISSN: 0361-1981

    Train delay incidents have major effects on transit service reliability and on customer satisfaction. Operators have long focused efforts on preventing such incidents. While this action is important, the fact that all transit operations inevitably face some degree of delay and disruption from incidents means that operators must also dedicate attention to reducing the duration of incidents and the time to restore normal operations after incidents occur. To be able to do this, it is necessary to measure the total impact of incidents on train service and customers. This research uses data from the CoMET and Nova metro benchmarking groups to investigate the ways in which transit operators can better measure the full effects of incidents on train service and customers. The key benefit of such a passenger-focused approach is that it enables transit managers to direct resources for incident response and recovery better, as well as support the case for strategic investments. This research has shown that most operators measure and report only the frequency of incidents. Of the 22 metros interviewed, only two were able to provide detailed data to estimate the number of passengers affected by incidents. It is no coincidence that the only two metros able to provide detailed data are in fact two of the most reliable in the group.
  • Journal article
    Trompet M, Parasram R, Anderson RJ, 2013,

    Benchmarking Disaggregate Customer Satisfaction Scores Between Bus Operators In Different Cities and Countries

    Directly comparing the satisfaction of customers of urban bus operators in different cities and countries is methodologically challenging due to the different surveys used, different sample frames, different response collection methods and the possibility of cultural bias. Nonetheless, due to the importance of customer satisfaction, the members of the International Bus Benchmarking Group started a research project in 2009 to overcome these challenges. The objective was for bus operators to understand the relative performance in meeting their customer’s expectations and to be able to target those areas in which they relatively underperform. Between 2009-2012, eight to ten participating organizations annually posted identical surveys on their website homepages in the same period. This paper describes the survey and data normalization methodology developed within the International Bus Benchmarking Group that provides managers of these organizations with a comparable view of their customer satisfaction. The described methodology has been successfully tested in the bus industry but can also be applied to other industries where there is a wish to benchmark customer satisfaction amongst other national and international peers.

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