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  • Conference paper
    Achurra Gonzalez PE, Angeloudis P, Zavitsas K, Niknejad SA, Graham DJet al., 2017,

    A Quantitative Framework for Assessment of Network Vulnerability in Liner Shipping Networks

    , Transportation Research Board 96th Annual Meeting
  • Journal article
    Morse L, Trompet M, Barron A, Graham DJet al., 2017,

    Development of a key performance indicator system to benchmark relative paratransit performance

    , Transportation Research Record-Series, Vol: 2650, Pages: 1-8, ISSN: 0361-1981

    The Americans with Disabilities Act of 1990 prohibits discrimination against people with disabilities. US transit agencies are therefore required to offer services to eligible customers that complement the mobility opportunities provided to the general public on fixed-route public transit. While these paratransit services are necessary and just, they represent a proportionally large cost to agencies: approximately eight times the cost per boarding compared to fixed-route bus service. To be able to identify opportunities for (cost) efficiencies, and to further improve the quality of paratransit services offered, the twenty agencies of the American Bus Benchmarking Group (ABBG) decided to benchmark their relative performance in paratransit management and operations. To ensure comparability of agencies’ performance and hence ensure the usefulness of the benchmarking program, a key performance indicator system was developed and associated data items were defined in detail. The scope of this system went beyond the data already provided to the National Transit Database, both in amount and granularity of data collected, as well as the detail of definitions. This paper describes the challenges, respective solutions, and other lessons identified during four years of paratransit benchmarking development led by Imperial College London, the ABBG facilitators. The paper provides transit agencies and authorities as well as benchmarking practitioners and academics an opportunity to apply these lessons for the further benefit of paratransit services and their customers around the U.S.

  • Journal article
    Horcher D, Graham DJ, Anderson RJ, 2017,

    Crowding cost estimation with large scale smart card and vehicle location data

    , Transportation Research Part B: Methodological: an international journal, Vol: 95, Pages: 105-125, ISSN: 0191-2615

    Crowding discomfort is an external cost of public transport trips imposed on fellow passengers that has to be measured in order to derive optimal supply-side decisions. This paper presents a comprehensive method to estimate the user cost of crowding in terms of the equivalent travel time loss, in a revealed preference route choice framework. Using automated demand and train location data we control for fluctuations in crowding conditions on the entire length of a metro journey, including variations in the density of standing passengers and the probability of finding a seat. The estimated standing penalty is 26.5% of the uncrowded value of in-vehicle travel time. An additional passenger per square metre on average adds 11.9% to the travel time multiplier. These results are in line with earlier revealed preference values, and suggest that stated choice methods may overestimate the user cost of crowding. As a side-product, and an important input of the route choice analysis, we derive a novel passenger-to-train assignment method to recover the daily crowding and standing probability pattern in the metro network.

  • Journal article
    Li H, Graham DJ, Liu P, 2016,

    Safety effects of the London cycle superhighways on cycle collisions

    , Accident Analysis & Prevention, Vol: 99, Pages: 90-101, ISSN: 0001-4575

    This paper evaluates the effects of the London Cycle Superhighways (CS) on cycle collisions. A total of 45 CS segments and 375 control segments are observed for a period of 8 years in London. Variables such as road characteristics, crash history and socio-economic in formation are included in the data set. Traffic characteristics Including traffic volume, cycle volume and traffic speed are obtained from Department for Transport. We first estimate the safety effects on the CS routes using Empirical Bayes methods. Then propensity score matching methods are also applied for comparison. The introduction of cycle superhighways caused cycling traffic volumes to increase dramatically along CS routes with no significant impacts on collision rates. Our models find that the increase in traffic was associated with a rise in annual total cycle collisions of around 2.6 per km (38% in percentage). However, when we re-estimate the effects based on cycle collision rates rather than levels, our results also show that the CS routes are not more dangerous or safer than the control roads. Among the four CS routes, CS3 performs the best in protecting cyclists with a large proportion of segregated lanes whilst the cyclists have to share the lanes with motorists on other routes. It is recommended that consistent safety designs shouldbe applied on all CS routes for a safer cycling environment.

  • 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.

  • Journal article
    Karathodorou N, Condry BJ, 2016,

    Choosing Optimal Reliability Measures for Passenger Railways: Different Measures for Different Purposes

    , Transportation Research Record, Vol: 2596, Pages: 1-9, ISSN: 0361-1981

    Reliability is one of the top factors influencing customer satisfaction with passenger rail services. It affects the level of demand for the service as passengers place a large negative value on delays. This matters to service providers, as it drives the fare revenue, and to policy makers as it influences mode share. This paper comprises a review of literature on reliability measurement in public transport, the results of a global survey of suburban rail operators and an assessment of the value of specific reliability measures. Reliability measures are typically required for three distinct purposes: internal measurements to manage the service, reporting to governments/authorities or franchisors for regulatory purposes and external reporting to customers and the media. Different measures may be optimal for each of these purposes and careful consideration is required for their definition and use. However, most railways surveyed chose their reliability measures either based on regulatory obligations or simply because these were used elsewhere.

  • 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.
  • 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.
  • 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, Mohammad SI, Graham DJ, Melo PCet al., 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, Trompet M, 2015,

    Propulsion technology trends across major bus operators in Europe, North America and South-East Asia

    , 43rd European Transport Conference
  • 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
  • Journal article
    Brage-Ardao R, graham DJ, Anderson RJ, 2015,

    Determinants of Train Service Costs in Metro Operations

    , Transportation Research Board 94th Annual Meeting
  • 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
  • Conference paper
    Sidiropoulos S, Majumdar A, Ochieng W, Schuster Wet al., 2014,

    Levels of organisation in Multi-Airport System

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

    Quantifying causal effects of road network capacityexpansions on traffic volume and density via a mixedmodel 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?

  • Conference paper
    Trompet M, Anderson, Richard, Graham, Daniel J, Condry, Benet al., 2014,

    Performance Benchmarking: Lessons Learned from Years of International Transit Benchmarking

    , Transportation Research Board
  • Journal article
    Moradi R, Schuster W, Feng S, Ochieng Wet al., 2014,

    A new carrier phase multipath mitigation technique for ionosphere-free combination

    , Institute of Navigation International Technical Meeting 2014, ITM 2014, Pages: 562-567

    The ionosphere layer of the atmosphere impacts the speed of electromagnetic waves such as those used by Global Navigation Satellite Systems (GNSS). If dual frequency measurements are available, the dependency of ionospheric errors on the frequency can be exploited to remove a significant fraction of these errors using the ionosphere-free (IF) combination. However, although such combination reduces the ionosphere-induced errors significantly, it also magnifies the noise and multipath errors. A new IF multipath mitigation technique is developed in this paper. In this technique, mitigation is achieved by extracting Inter Frequency carrier Multipath (IFM) errors for Global Positioning System (GPS) L1 and L2 and removing them from the IF carrier phase observation. Three test scenarios with different baselines were conducted using real data sets collected in static mode, and post processed in Real-Time Kinematic (RTK) mode. By mitigating the multipath errors in the ionosphere-free combination using the new technique developed in this paper, the horizontal Root Mean Square (RMS) error was reduced by 27% to 45% and the horizontal mean errors were reduced by 25% to 33%.

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