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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jue.2006.10.001 Byline: Daniel J. Graham Keywords: Agglomeration; Productivity; Congestion; Translog Abstract: This paper investigates the links between returns to urban density, productivity and road traffic congestion. A generalised translog production-inverse input demand function is estimated to test for the existence of variable returns to agglomeration in manufacturing, construction and service industries. Two separate measures of urban density, in which proximity is represented by straight line distance or by generalised cost, are constructed and included in the translog to identify the effect of road traffic congestion. The results show that for some sectors of the economy diminishing returns to urban density can set in causing the magnitude of agglomeration elasticity to fall as effective densities increase. The generalised cost based measure of agglomeration produces higher elasticities because it captures both time and distance dimensions of density. A comparison of spatial variance in estimates indicates that road traffic congestion plays an important role in explaining diminishing returns for the most highly urbanised locations. Author Affiliation: Centre for Transport Studies, Imperial College London, London SW7 2AZ, UK Article History: Received 22 June 2006; Revised 25 October 2006

This study assesses whether the negative exogenous informational shock of the MeToo scandal has affected women's perception of security. The MeToo movement was first reported in the media worldwide in October 2017, and has received enormous press coverage since then. The exogenous and unanticipated nature of the scandal provides a natural experiment that we can use to quantify how wider external information affects 'ordinary' women's perceptions of security and their willingness to report feelings of dissatisfaction with security levels. To do so, we use a case study of women's' perception of security in 12 metro systems in Europe, for which we have large-scale unique customer satisfaction data over the years 2014 to 2018. We use interview dates to determine perceptions pre and post scandal, and we take the MeToo scandal as a 'treatment' affecting women in the sense that they were the primary target of the informational shock. Using pre and post treatment data, for our defined treated (women) and control (men) units, we apply a difference-in-differences estimator to identify the impact of the scandal on perceptions of security. Our results show a 2.5% increase in the probability of women being dissatisfied with security in stations and in metro carriages post-scandal. These results support the conclusion that revealed preferences are only revealed up to a certain extent. A change in the context (e.g. , an informational shock), can alter perceptions and in turn, can encourage individuals to disclose lower (or higher) satisfaction levels as perceptions of the norm change. [ABSTRACT FROM AUTHOR]

In this paper we use large-scale mass transit data to improve the journey time performance measurement of urban bus systems. For low frequency bus services, the application of on-time performance (OTP) metrics, particularly the location and number of stops to sample, varies greatly across operators, which can lead to biased estimates. In this paper, we aim to address sampling disparity, and propose a new statistically robust sampling scheme to ensure representative, non-biased, and comparable measurement of route level on time performance (OTP) which enables the inclusion of operators with sparse data in benchmarking activities. We use automated vehicle location data and analyse 59 unique low frequency route-direction data sets from 9 international bus operators. Across all route-direction data sets, an average of 28% of stops are required to be sampled under the defined sampling scheme to achieve a 95% confidence level of sampling the route-level mean within a ± 5% range of accuracy. By including data on additional routes, the analysis can be further refined and generalised to enable progressive improvement of inter-operator comparability and benchmarking. [ABSTRACT FROM AUTHOR]

• Estimated the causal economic impact of an off-peak fare discount in Hong Kong. • Applied the difference-in-difference method to control for confounding bias. • Found the aggregate effect to be small but statistically significant and heterogeneous. • Responsiveness was governed by travel costs and crowding. • Produced novel causal estimates of trip rescheduling elasticities. This paper quantifies the causal impact of differential pricing on the trip-scheduling of regular commuters using the Mass Transit Railway (MTR) in Hong Kong. It does so by applying a difference-in-difference (DID) method to large scale smart card data before and after the introduction of the Early Bird Discount (EBD) pricing intervention. We find statistically significant but small effects of the EBD in the form of earlier departure times. Leveraging the granularity of the data, we also allow for the treatment effect to vary over observed travel characteristics. Our empirical results suggest that fares and crowding are the key determinants of commuter responsiveness to the EBD policy. [ABSTRACT FROM AUTHOR]

• Estimated a short-run cost function for urban rail transport (i.e. metro) operations • Used a unique panel dataset of 24 metro operations from across the globe. • Addressed various endogeneity challenges in such empirical analysis. • Found metro systems with high density of usage to be the most cost-efficient. • Provided new insights into existence of economies of scale in metro operations. There is considerable variation in the average cost of operations across urban rail transport (or metro) systems. Since metros are typically owned and operated by public authorities, there is a public interest case in understanding the key drivers of their operational costs. This paper estimates short-run cost functions for metro operations using a unique panel dataset from twenty-four metro systems around the world. We use a flexible translog specification and apply dynamic panel generalised method of moments (DPGMM) estimation to control for confounding from observed and unobserved characteristics of metro operations. Our empirical results show that metro systems with a high density of usage are the most cost-efficient. We also find that operational costs fall as metro size increases. These results have important implications for the economic appraisal of metro systems. [ABSTRACT FROM AUTHOR]

• This study presents the first macro-level cross-country analysis of urban rail transit safety. • The study utilizes an international dataset from 31 systems to analyze the operational safety of urban rail. • This study applies supervised machine learning models which consider the socio-technical nature and non-linear interactions. • This study provides a benchmarking model for urban rail transit safety outputs which accommodates heterogeneity. This paper studies the operational safety of urban rail transit (URT) systems through Artificial Neural Networks. While recent safety literature adopting systematic models of analysis consider the complexity of URT operations, they focus on single systems or single components of the operational process. Our study contributes to the URT safety literature by having a macro perspective, while considering that such complex socio-technical systems involve multiple non-linear interactions among their components. To our knowledge, we present the first cross-country analysis of URT safety through machine learning models in the literature, using a unique international dataset from 31 URT systems which comprises annual system-level data. Two models are estimated to predict the annual URT injuries. The first model includes safety-related incidents as inputs, while the second includes operational characteristics of the system. Additionally, a closed-form formula is presented to predict the annual number of injuries based on operational features of the URT system along with an illustrative example to demonstrate benchmarking applications. The results are promising and indicate good generalizability. The models proposed in this study could be useful for operators and policy makers as they aid in prioritizing improvements, predicting future safety performance based on changes in operational features, and as a benchmarking tool. [ABSTRACT FROM AUTHOR]

• We compare the performance of EB and PS methods via simulation studies. • PS models perform well with large samples and sufficient balance in covariates. • The EB estimators can be biased when units follow different SPFs. • DR models allow for violation of assumptions and provide additional robustness. Statistical evaluation of road safety interventions can be undertaken using a variety of different approaches, typically requiring different assumptions to obtain causal identification. In this paper, we conduct a simulation study to compare the performance of empirical Bayes (EB) and propensity score (PS) based methods, which have featured prominently in the recent literature, in settings with and without violation of key assumptions. The estimators considered include EB, inverse probability weighting (IPW), and Doubly Robust (DR) estimation. We find that while the EB approach has good finite sample properties when model assumptions are met, the consistency of this estimator is substantially diminished when the reference and treated sites follow different functions. The IPW estimator performs well in large samples, but requires a correctly specified PS model with sufficient overlap in covariate distributions between treated and control units. The DR estimator allows for violation of assumptions in either the regression or PS model, but not both. We find that this added level of robustness affords overall better performance than attained via EB or IPW estimation. [ABSTRACT FROM AUTHOR]

Abstract This paper quantifies the substitution and complementary effects of high-speed rail (HSR) on air travel demand in terms of both route traffic and airport enplanement. Employing the difference-in-differences (DID) method, the first part of the analysis measures the effect of new HSR routes on parallel air route traffic with a focus on East Asian regions (Mainland China, Japan, South Korea, and Taiwan). The second part examines the effect of air-HSR integration on passenger enplanement at East Asian airports and compares with that in the Central European market. We find that in general the airport's access cost (reflected by the distance from central city) has a negative impact on the air traffic. The substitution effects of HSR are the most significant on short- and medium-haul (below 1000 km) air routes while introducing HSR services has encouraged long distance (over 1000 km) air travels in Mainland China. The complementary effect is investigated in the context of air-HSR integration, which has significantly positive impacts on airport enplanement at primary hub airports when fitted with on-site HSR links. The benefit is limited at secondary hubs and regional airports possibly by locations and HSR service frequencies. [ABSTRACT FROM AUTHOR]

This paper investigates multi-period public transport supply, i.e. networks in which capacity cannot be differentiated between links and time periods facing independent but nonidentical demand conditions. This setting is particularly relevant in public transport, as earlier findings on multi-period road supply cannot be applied when the user cost function, defined as the sum of waiting time and crowding costs, is nonhomogeneous. The presence of temporal, spatial and directional demand imbalances is unavoidable in a public transport network. It is not obvious, however, how the magnitude of demand imbalances may affect its economic and financial performance. We show in a simple back-haul setting with elastic demand, controlling for total willingness to pay in the network, that asymmetries in market size reduce the attainable social surplus of a service, while variety in maximum willingness to pay leads to higher aggregate social surplus and lower subsidy under efficient pricing. The analysis of multi-period supply sheds light on the relationship between urban structure, daily activity patterns, and public transport performance. [ABSTRACT FROM AUTHOR]

Seated and standing travelling imply significantly different experience for public transport users. This paper investigates with analytical modelling and numerical simulations how the optimal seat supply depends on demand and supply characteristics. The paper explores the implications of seat provision on the marginal cost of travelling as well. In crowded conditions, we distinguish two types of external costs: crowding density and seat occupancy externalities. We derive, using a realistic smart card dataset, the externality pattern of a metro line, and identify the distorting role of the occupancy externality that makes the welfare maximising fare disproportionate to the density of crowding. [ABSTRACT FROM AUTHOR]

In this paper we consider a fiscal federation and study the effects of decentralised provision of loss-generating public services with benefit spillovers to other regions. We use public transport provision across administrative borders as a prototype example. We show in a formal model that local governments might be better off when a higher-level government or a neighbouring region provides these services, and even privatisation to a monopolist can be preferred over decentralisation. Our model reveals that these results are governed by a variant of the tax exporting mechanism that applies to subsidised services, i.e., the possibility that local consumers can exploit spillover benefits without contributing to the subsidy burden of service provision. Public transport provision is one of the large sectors of public policy where decentralisation could provide social benefits, but, as the paper reveals, the need for subsidies generates a genuine conflict of interest between the governments involved. • We model the provision of subsidised public services in a fiscal federation. • New insight: local governments may be against decentralised service provision. • We find tension between preference matching and deficit sharing objectives. • The results provide explanation for failures in public service decentralisation. [ABSTRACT FROM AUTHOR]

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 information 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 should be applied on all CS routes for a safer cycling environment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Using abnormal headway deviations as the indicator of metro disruptions. • A probabilistic, unsupervised and automatic detection method based on Gaussian mixture models and large-scale vehicle location data. • A novel algorithmic solution to empirically identify the propagation of disruption and the recovery intervention from operators. • The proposed framework is effective for any type of service interruption, including minor delays of just a few minutes. Urban metro systems are often affected by disruptions such as infrastructure malfunctions, rolling stock breakdowns and accidents. The crucial prerequisite of any disruption analytics is to have accurate information about the location, occurrence time, duration and propagation of disruptions. To pursue this goal, we detect the abnormal deviations in trains' headway relative to their regular services by using Gaussian mixture models. Our method is a unique contribution in the sense that it proposes a novel, probabilistic, unsupervised clustering framework and it can effectively detect any type of service interruptions, including minor delays of just a few minutes. In contrast to traditional manual inspections and other detection methods based on social media data or smart card data, which suffer from human errors, limited monitoring coverage, and potential bias, our approach uses information on train trajectories derived from automated vehicle location (train movement) data. As an important research output, this paper delivers innovative analyses of the propagation progress of disruptions along metro lines, which enables us to distinguish primary and secondary disruptions as well as effective recovery interventions performed by operators. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper estimates demand elasticities for diesel fuel in the UK using static error correction and dynamic ADL time series cointegration models. While there are studies focusing on elasticities in the road transport sector, most have either looked at petrol demand or have used road transport fuel demand. Our findings indicate that the income elasticities for diesel fuel, both in the short- and the long-run are significantly higher, and the long run price elasticity is relatively lower as compared to those reported in studies using fuel or petrol demand. [ABSTRACT FROM AUTHOR]

Highlights: [•] We use propensity score matching to evaluate the safety effect of speed cameras. [•] The propensity score can be used as the criteria for selecting the reference group. [•] Propensity score matching can improve the performance of the empirical Bayes. [•] Speed cameras are most effective up to 200m from camera sites. [ABSTRACT FROM AUTHOR]

Abstract: The literature on land and property values demonstrates a great deal of variability in the estimated change in values arising from rail investments. This paper conducts a meta-analysis on empirical estimates from 23 studies (102 observations) that analysed the impact of rail on land/property value changes. Variation in the estimated impacts is calculated and discussed in relation to key dimensions of study-design characteristics. The results show that a number of factors produce significant variations in the estimates. These include the type of land use, the type of rail service, the rail system life cycle maturity, the distance to stations, the geographical location, accessibility to roads, methodological characteristics, as well as whether the impacted area is land or property. On the other hand, we observe that changes in purchase price and rent values due to rail projects are statistically similar to each other, that there is no evidence of change in values over time nor due to the location of land/property within the city, and that including property characteristics and neighbourhood type in the estimation model do not change values significantly. Publication bias tests are also performed and show that although researchers tend to report both positive and negative results, they tend to be biased towards statistically significant estimates. [Copyright &y& Elsevier]

Abstract: This paper aims to identify the impacts of the London congestion charge on road casualties within the central London charging zone. It develops a full difference-in-difference (DID) model that is integrated with generalized linear models, such as Poisson and Negative Binomial regression models. Covariates are included in the model to adjust for factors that violate the parallel trend assumption, which is critical in the DID model. The lower Bayesian Information Criterion value suggests that the full difference-in-difference model performs well in evaluating the relationship between road accidents and the London congestion charge as well as other socio-economic factors. After adjusting for a time trend and regional effects, the results show that the introduction of the London congestion charge has a significant influence on the incidence of road casualties. The congestion charge reduces the total number of car accidents, but is associated with an increase in two wheeled vehicle accidents. [Copyright &y& Elsevier]

In recent years, urban rail funding has become an increasing concern in some western cities. The underlying issues over ridership and funding has largely been driven by trends such as increasing teleworking and new transport modes like ridesharing, which are likely to further exacerbate funding issues in the aftermath of the worldwide health crisis. This paper contributes to the discussion through the examination of funding within urban rail transport, specifically the strengths and weaknesses of mechanisms that can be used to achieve sustainable, stable long-term funding. A unique, very long-term historical dataset of five large metros around the world was collected for this research, with the analysis based on evidence of actual practices, from a relatively rare organisational perspective. Key results include: i) appropriate fare-setting has been critical for long-term financial health, but is vulnerable to inflation effects and political interference; indexing is important but use of consumer prices has led to revenue erosion in real terms, since wage growth is typically higher. ii) How subsidies are generated can have varying impacts on funding stability and sustainability — dedicated taxes and cross-subsidies from road charges are typically better than direct grants as they are secured by legislation; they also reduce political changes and avoid competing claims from other types of government spending (health, education), as compared with grants. iii) Commercial revenue can be a valuable source for future growth, in light of increased resistance to taxation. Real estate-related revenues in particular can be substantial, as in Hong Kong and Tokyo, with historically faster growth than wages, while also capturing any further value increases from rail system improvements. • Strengths and weaknesses analysis of funding sources, using data from 5 large metros • Fare-setting with appropriate index (wages) is crucial for long-term financial health • How subsidies are generated – intrinsic impacts on funds stability and sustainability • Ideally, subsidies secured multi-year with legislation – avoids competing claims • Real estate enables long-term value capture and revenue growth from rail improvements [ABSTRACT FROM AUTHOR]

Abstract: Since at least 1935, vision researchers have used art stimuli to test human response to complex scenes. This is sensible given the “inherent interestingness” of art and its relation to the natural visual world. The use of art stimuli has remained popular, especially in eye tracking studies. Moreover, stimuli in common use by vision scientists are inspired by the work of famous artists (e.g., Mondrians). Artworks are also popular in vision science as illustrations of a host of visual phenomena, such as depth cues and surface properties. However, until recently, there has been scant consideration of the spatial, luminance, and color statistics of artwork, and even less study of ways that regularities in such statistics could affect visual processing. Furthermore, the relationship between regularities in art images and those in natural scenes has received little or no attention. In the past few years, there has been a concerted effort to study statistical regularities in art as they relate to neural coding and visual perception, and art stimuli have begun to be studied in rigorous ways, as natural scenes have been. In this minireview, we summarize quantitative studies of links between regular statistics in artwork and processing in the visual stream. The results of these studies suggest that art is especially germane to understanding human visual coding and perception, and it therefore warrants wider study. [Copyright &y& Elsevier]

Abstract: The fuel demand literature provides a range of estimates of the long and short-run price and income elasticities of gasoline demand for different countries and states. These estimates can be very useful in predicting the overall impacts of policy approaches designed to reduce fuel consumption and to address concerns of carbon emissions or energy security. However, analysis of policy options based on elasticities that are homogenous across income groups provides no information about the relative distributional burden that may be faced by different sectors of the population. Different responses to the same change in price or income are likely to occur, dependent on both travel needs and income levels. This paper estimates gasoline demand elasticities for different income quintiles in the United States to test for heterogeneity in demand response. Group wise summary consumer expenditure data for 20 years is used to derive the elasticity estimates. The results show that the elasticities do vary across groups and follow a U-pattern from the lowest to the highest income quintile. The lowest income quintile is found to have the largest price elasticity. The lowest and the highest income quintiles appear to be statistically insensitive to any changes in income. The rebound effect also follows the U-pattern, with the highest rebound observed among the wealthiest households. Rural households appear to have lower price elasticity than households in urban areas. [Copyright &y& Elsevier]

Abstract: A dynamic panel model is used to estimate the effect that fares, income and quality of service have on demand for a sample of 22 urban metros. The estimated price elasticity is −0.05 in the short run and −0.33 in the long run. The estimated long run income elasticity is small but positive (0.18), indicating that metros are perceived as normal goods. The quality of service elasticities are positive and substantially higher than the absolute value of fare elasticities. The implication is that quality of service improvements, rather than fare reductions, may be more effective in increasing metro patronage. [Copyright &y& Elsevier]

Abstract: The personal road transport sector is one of the largest and fastest growing sources of CO2 emissions. This paper investigates a tradable permit policy for mitigating carbon emissions from personal road transport and discusses various issues of permit allocation. As tradable permits will effectively raise the price of fuel, the policy has important distributional implications. The distribution of burden depends on permit allocation strategies and on the consumer response to an increase in price. The behavioural response varies among different segments of the population depending on their travel needs, which in turn are contingent upon their income, location of residence and other factors. A model previously estimated by [Wadud, Z., Graham, D.J., Noland, R.B., 2007. Modelling gasoline demand for different socio-economic groups. In: Proceedings of the 86th Annual Meeting of the Transportation Research Board, Washington, DC, USA, January 2007] with group-wise aggregated US consumer expenditure survey data for 20 years provides behavioural responses for different income groups. The resulting welfare distribution in the USA is evaluated in this paper. Different permit allocation schemes are also considered in the analysis. [Copyright &y& Elsevier]

Abstract: The incidence of child injury due to road traffic accidents appears to be positively associated with socio-economic deprivation. However, the reasons behind this relationship have proven difficult to identify. In this paper, we present results from a cross-sectional analysis using generalized linear regression models of child pedestrian casualties for the wards of England. We find that there are distinct and substantial effects on casualty rates from characteristics associated with area deprivation across diverse environments. These associations exist over and above influences arising from local environmental characteristics. Distinct dimensions of deprivation appear to affect the incidence of pedestrian casualties to varying degrees and sometimes in different directions. The results identify a relationship between income deprivation and the incidence of child pedestrian casualties, but they also show that poverty is only one aspect of deprivation that matters. In particular, we find a consistent positive influence from crime related deprivation. [Copyright &y& Elsevier]

Abstract: This paper formulates and compares parametric productivity estimates and non-parametric efficiency scores for urban rail firms. It outlines a decomposition of total factor productivity (TFP) change and proposed some hypotheses about how this relates to an analysis of efficiency using data envelopment analysis (DEA). TFP is empirically evaluated using estimates from a translog production function. The estimation also tests some hypotheses about the elements that comprise firm specific ‘technology’. The results show that while estimates of returns to scale differ using the TFP and DEA methods, the ranking of urban rail efficiency is broadly similar. [Copyright &y& Elsevier]

The article cites an econometric analysis of metro station operating costs. An improved understanding of some of the major factors driving the said costs is provided. The strong system-specific influences which impact costs are detected to have positive associations from a range of station characteristics. The presence of air-conditioning is also found to have a substantial effect in increasing expected station operating cost by as much as 40%.

Abstract: To account for the spatial and temporal response properties of the retina, a number of studies have proposed that these properties serve to “whiten” the visual input. In particular, it has been argued that the sensitivity of retinal ganglion cells is matched to the spatial frequency spectrum of natural scenes, resulting in a flattened or “whitened” response spectrum across a range of frequencies. However, we argue that there are two distinct hypotheses regarding the flattening of the spectrum. The decorrelation hypothesis proposes that the magnitude of each ganglion cell tuning curve rises with spatial frequency, resulting in a flattened response spectrum for natural scene stimuli. With appropriate sampling, this scheme allows neighboring neurons to be uncorrelated with each other. The response equalization hypothesis proposes that the overall response magnitude of neurons increases with spatial frequency. The proposed goal of this model is to allow neurons with different receptive field sizes to produce the same average response to natural scenes. The response equalization hypothesis proposes an explanation for the relative gain of different ganglion cells and we show that this proposal fits well with published data. We suggest that both hypotheses are important in understanding the tuning and sensitivity of ganglion cells. However, using a simulation, both models are shown to be insufficient to explain the center-surround receptive field organization of ganglion cells. We discuss other factors, including representational sparseness, which could be related to the goals of ganglion cell spatial processing. We suggest three constraints needed to describe the basic linear properties of P-type ganglion cells: decorrelation, response equalization, and a minimal wiring or minimal size constraint. [Copyright &y& Elsevier]

Abstract: This paper explores the effects of road user charging throughout England. It develops a model to test charging scenarios including revenue raising and revenue neutral charging options, and economically efficient pricing. For each scenario we estimate effects on traffic volumes, user charges and fares, subsidies, environmental costs, benefits to consumers, government revenue, and overall net benefits. We show that appropriate charging structures coupled with compensating reductions in existing motoring taxes can make a real difference to traffic growth, congestion and environmental damage, and can relieve pressure to build new roads. [Copyright &y& Elsevier]

This paper examines economies of scale and density in urban rail transport. It isolates the effects of constant and non-constant returns on output and productivity growth using data relating to 17 rail systems in cities around the world. Estimates reveal constant returns to scale but increasing returns to density. The productivity model shows that total factor productivity change has been of great importance in differentiating the output performance of urban rail systems. Our analysis of average labour productivity confirms the importance of shifts to other factors of production and technological change in explaining changing levels of output per worker. [Copyright &y& Elsevier]

The surface of a biomaterial plays a critical role in the success of an implant. Much effort is currently being focused on controlling the chemistry at biomaterial surfaces to ensure favorable results in vivo. The successful tailoring of the surface chemistry will require a detailed surface characterization to verify that the desired changes have been made. This will include the ability to determine the composition, structure, orientation, and spatial distribution, of the molecules and chemical structures on the surface. TOF-SIMS is a powerful surface characterization technique that is able to address these requirements through both spectral analysis and direct chemical state imaging. The flexibility of the TOF-SIMS technique, and the wealth of data produced have generated much interest in its use for biomaterial characterization. This review discusses the strengths, weaknesses, and challenges of static TOF-SIMS for biomaterial surface characterization. First the basic principles of TOF-SIMS are introduced, giving an overview of the technique. Next, sample type, and other sample considerations are discussed. Then data interpretation is overviewed using examples from both spectral and imaging data. Finally, quantitative SIMS analysis is discussed and an outlook for TOF-SIMS analysis of biomaterials will be given. [Copyright &y& Elsevier]

• Passenger arrival patterns are quantified as a function of headway using AFC and AVL data. • For 3 central London lines, arrivals transition from random to non-random at 2–3 min headways. • Using updated arrival patterns, degree of density economies is milder than what literature suggests. In this paper, we investigate the influence of train headways on passenger platform wait times using automated data from the London Underground metro system. For high frequency services, the literature suggests that passenger arrivals are random and that under perfectly random conditions with all other factors held constant, wait times are equivalent to half of the headway between trains. We test this hypothesis using large-scale smart card and vehicle location data, which enables the extraction of access times from total passenger journey times as well as the precise measurement of train headways. Using a semiparametric regression modelling framework, we generate non-linear estimates of the relationship between access times and headway while conditioning for other service supply and demand factors. Marginal platform wait times are then derived numerically via an exposure–response model framework which accounts for potential confounding between the walking and waiting components of access times, thus enabling quantification of the unbiased impact of headways on wait times. For three lines in central London, we observe that marginal wait times transition from greater than half of the headway to approximately one third of the headway as train frequencies decrease. The transition occurs in the range between 2-3 min headways, lower than earlier estimates in the literature. A series of numerical simulations illustrate the importance of waiting time sensitivity in the optimisation of public transport services. In comparison with the standard wait time assumption, our exercise reveals that the degree of density economies is milder than what the literature suggests, and this may neutralise some of the economic justifications of high public transport subsidies. [ABSTRACT FROM AUTHOR]

Public transport is commonly associated with benefits such as reducing road traffic congestion and improving air quality. This paper focuses on evaluating the causal impact of a new public transport provision in London, the Jubilee Line Extension (JLE) in 1999, on air quality. Using meteorological normalisation and a regression discontinuity design with time as the forcing variable, we show that the JLE led to only small changes in air pollution at some specific locations; detectable changes in NO x , NO 2 , and O 3 concentrations were found at 63%, 43% and 29% of air pollution monitoring sites, respectively. For those sites where a change in pollution was detected, the responses ranged from −2% to +1% for NO 2 and -1% to 0% for O 3. We calculate that the long-run effects are greater, ranging from −11% to +3% for NO 2 and from −2% to +2% for O 3 at sites that showed a response to the JLE. Aggregating across all sites in London for a city-wide effect, both short and long-run effects were less than 1% or insignificant. We find statistically significant increases in NO 2 and O 3 concentrations at some background sites, but the magnitude of effect is within +1% in the short-run and +3% in the long-run. Our analysis shows that the effect of the JLE on air pollution in some areas was greater than others, however across London the effect was small and this indicates that public transport provision on its own is not an effective strategy to improve air quality. • An increase in public transport supply did not improve air quality at all sites. • Public transport provision on its own is not effective to improve air quality. • Short-run changes in pollution concentrations ranged from −2% to +1%. • Long-run changes in pollution concentrations may range from −11% to +3%. [ABSTRACT FROM AUTHOR]

Air transport capacity expansions are often justified on the grounds that they will improve economic performance and induce growth. Such causal impacts are hard to identify empirically due to the fundamentally endogenous nature of the relationship between air transport and the economy. This paper contributes to the empirical literature on aviation-economy effects by conducting a case study of the impacts of air transportation activity on productivity in Chinese provinces. For exogenous variation we exploit a policy scenario created by the 2003 deregulation of the Chinese aviation sector, which was applied in all provinces of China except Beijing and Tibet. We find that this policy intervention resulted in substantial growth in air transport passengers and cargo. We estimate the causal effect of air transport on productivity by comparing GDP per employee in Tibet relative to a synthetic control region affected by the deregulation policy. We find a significant positive productivity effect from aviation expansion following the 2003 deregulation. Use of a differences-in-differences specification confirms this result. • We study the causal effects of air transportation on the economy. • We exploit a scenario created by the 2003 deregulation of the Chinese aviation sector. • The policy was applied in all provinces of China, except in Beijing and Tibet. • We use synthetic control methods to compare Tibet relative to regions affected by the policy. • We find that GDP per employee was significantly lower in Tibet due to the policy exclusion. [ABSTRACT FROM AUTHOR]

Proponents of the Mobility as a Service concept claim that subscriptions to alternative modes can effectively reduce car ownership and the adverse effects of underpriced car use. We test this hypothesis in a microeconomic model with endogenous mode choice as well as car and subscription ownership. The model contains congestible urban rail and car sharing options as substitutes of underpriced private car use. We find that aggregate car ownership is not a reliable proxy for road congestion: subscriptions may reduce car ownership while increasing the vehicle miles travelled by remaining car owners. Subscriptions induce welfare losses for two reasons. First, pass holders overconsume the alternative modes, as the marginal fare they face drops to zero. Second, non-pass holders tend to shift to car use due to the crowding induced by pass holders, causing additional distortions. We illustrate numerically that differentiated pricing is more efficient in achieving the goals of MaaS. • The paper tests whether multimodal MaaS subscriptions are efficient pricing tools. • Car and subscription ownership as well as mode choice are endogenous in our model. • We find that car ownership is not a reliable proxy for the degree of car congestion. • Subscription holders overconsume PT, and push non-pass holders towards car use. • Differentiated usage-dependent pricing achieves the goals of MaaS more efficiently. [ABSTRACT FROM AUTHOR]

This paper is concerned with the Wider Economic Impacts (WEIs) of transport improvements that arise via scale economies of agglomeration. It reviews the background theory and empirical evidence on agglomeration, explains the link between transport and agglomeration, and describes a three step procedure to appraise agglomeration impacts in a number of different settings. It includes new analytical work on measures of agglomeration and reports agglomeration-productivity elasticity estimates for the UK not previously published in the academic literature. The paper concludes with a set of recommendations for future empirical work on agglomeration and transport appraisal. • Paper is concerned with the Wider Economic Impacts (WEIs) of transport improvements that arise via scale economies of agglomeration. • It reviews the background theory and empirical evidence on agglomeration and explains the link between transport and agglomeration, it describes a three step procedure to appraise agglomeration impacts in a number of different settings. • It includes new analytical work on measures of agglomeration and reports agglomeration-productivity elasticity estimates for the UK not previously published in the academic literature. [ABSTRACT FROM AUTHOR]

The state of infrastructure in many developed countries around the world is an increasingly pressing issue, with mounting costs the longer repairs are deferred. In today's rapidly urbanising world, the urban rail network is particularly critical, since infrastructure failures can have severe economic consequences for both the operator's finances and user time costs. This paper thus provides a system-level model of welfare-oriented supply optimisation that integrates asset management with the literature on optimal pricing and capacity provision. Using a simulation approach and calibrating with London Underground data, this paper delivers three key contributions. First, the economic efficiency of long-term capital planning is highlighted, with up to an 87% welfare gain when comparing a 40- versus 5-year planning horizon. Second, in general, the longer the planning horizon, the higher the annual welfare, demand, asset condition, fare and supply, in the steady-state. Third, the analysis explores why policies in reality diverge from the welfare optimum: we show that election cycles can have a detrimental effect, with increased asset neglect and volatility in spending. Economic efficiency improves in the short-term at the expense of the long-term; significant intervention is needed to break this downwards trend, as also reflected in various rail systems' histories. [ABSTRACT FROM AUTHOR]