The role of accident exposure in transport system safety evaluations I: Intersection and link site exposure

Realistic predictions of the likely safety performance of advanced transport systems will need to draw on the knowledge accumulated from a large number of safety evaluations which have already been undertaken for existing transport systems. In particular, safety evaluations of future technologies must avoid the methodological pitfalls experienced in extensively researched areas, such as road safety, if such evaluations are to be meaningful. This paper reviews the use of exposure for a broad range of road safety studies, and concludes that unsatisfactory treatment of exposure is a common failing in past evaluations of the effectiveness of road accident countermeasures. Whilst a broad range of safety analyses is discussed, the use of exposure in site safety studies is emphasized. A follow-up paper will extend the discussion to other aspects of accident exposure including exposure measures for large groups of transport system users.     

Importance and exposure in road network vulnerability analysis

The reliability and vulnerability of critical infrastructures have attracted a lot of attention recently. In order to assess these issues quantitatively, operational measures are needed. Such measures can also be used as guidance to road administrations in their prioritisation of maintenance and repair of roads, as well as for avoiding causing unnecessary disturbances in the planning of roadwork. The concepts of link importance and site exposure are introduced. In this paper, several link importance indices and site exposure indices are derived, based on the increase in generalised travel cost when links are closed. These measures are divided into two groups: one reflecting an “equal opportunities perspective”, and the other a “social efficiency perspective”. The measures are calculated for the road network of northern Sweden. Results are collected in a GIS for visualisation, and are presented per link and municipality. In view of the recent great interest in complex networks, some topological measures of the road network are also presented.     

Air traffic assignment to reduce population noise exposure using activity-based approach

Aircraft noise has been regarded as one of the major environmental issues related to air transport. Many airports have introduced a variety of measures to reduce its impact. Several air traffic assignment strategies have been proposed in order to allocate noise more wisely. Even though each decision regarding the assignment of aircraft to routes should consider population exposure to noise, none of the air traffic assignment strategies has addressed daily migrations of population and number of people exposed to noise. The aim of this research is to develop a mathematical model and a heuristic algorithm that could assign aircraft to departure and arrival routes so that number of people exposed to noise is as low as possible, taking into account temporal and spatial variations in population in an airport’s vicinity. The approach was demonstrated on Belgrade airport to show the benefits of the proposed model. Numerical example showed that population exposure to noise could be reduced significantly by applying the proposed air traffic assignment model. As a consequence of the proposed air traffic assignment, overall fuel consumption increased by less than 1%.     

Exposing the role of exposure: Public transport network risk analysis

Network risk assessment takes into consideration the probability that adverse events occur and the impacts of such disruptions on network functionality. In the context of transport networks, most studies have focused on vulnerability, the reduction in performance indicators given that a disruption occurs. This study presents and applies a method to explicitly account for exposure in identifying and evaluating link criticality in public transport networks. The proposed method is compared with conventional measures that lack exposure information. A criticality assessment is performed by accounting for the probability of a certain event occurring and the corresponding welfare loss. The methodology was applied for a multi-modal public transport network in the Netherlands where data concerning disruptions was available. The results expose the role of exposure in determining link criticality and overall network vulnerability. The findings demonstrate that disregarding exposure risks prioritizing links with high passenger volumes over links with a higher failure probability that are significantly more critical to network performance. The inclusion of exposure allows performing a risk analysis and has consequences on assessing mitigation measures and investment priorities.     

Marginal costs of freeway traffic congestion with on-road pollution exposure externality

The health cost of on-road air pollution exposure is a component of traffic marginal costs that has not previously been assessed. The main objective of this paper is to introduce on-road pollution exposure as an externality of traffic, particularly important during traffic congestion when on-road pollution exposure is highest. Marginal private and external cost equations are developed that include on-road pollution exposure in addition to time, fuel, and pollution emissions components. The marginal external cost of on-road exposure includes terms for the marginal vehicle’s emissions, the increased emissions from all vehicles caused by additional congestion from the marginal vehicle, and the additional exposure duration for all travelers caused by additional congestion from the marginal vehicle. A sensitivity analysis shows that on-road pollution exposure can be a large portion (18%) of marginal social costs of traffic flow near freeway capacity, ranging from 4% to 38% with different exposure parameters. In an optimal pricing scenario, excluding the on-road exposure externality can lead to 6% residual welfare loss because of sub-optimal tolls. While regional pollution generates greater costs in uncongested conditions, on-road exposure comes to dominate health costs on congested freeways because of increased duration and intensity of exposure. The estimated marginal cost and benefit curves indicate a theoretical preference for price controls to address the externality problem. The inclusion of on-road exposure costs reduces the magnitudes of projects required to cover implementation costs for intelligent transportation system (ITS) improvements; the net benefits of road-pricing ITS systems are increased more than the net benefits of ITS traffic flow improvements. When considering distinct vehicle classes, inclusion of on-road exposure costs greatly increases heavy-duty vehicle marginal costs because of their higher emissions rates and greater roadway capacity utilization. Lastly, there are large uncertainties associated with the parameters utilized in the estimation of health outcomes that are a function of travel pollution intensity and duration. More research is needed to develop on-road exposure modeling tools that link repeated short-duration exposure and health outcomes.     

Roadway determinants of bicyclist exposure to volatile organic compounds and carbon monoxide

Few studies have quantified relationships between bicyclist exposure to air pollution and roadway and traffic variables. As a result, transportation professionals are unable to easily estimate exposure differences among bicycle routes for network planning, design, and analysis. This paper estimates the effects of roadway and travel characteristics on bicyclist exposure concentrations, controlling for meteorology and background conditions. Concentrations of volatile organic compounds (VOC) and carbon monoxide (CO) are modeled using high-resolution data collected on-road. Results indicate that average daily traffic (ADT) provides a parsimonious way to characterize the impact of roadway characteristics on bicyclists’ exposure. VOC and CO exposure increase by approximately 2% per 1000 ADT, robust to different regression model specifications. Exposure on off-street facilities is higher than at a park, but lower than on-street riding – with the exception of a path through an industrial corridor with significantly higher exposure. VOC exposure is 20% higher near intersections. Traffic, roadway, and travel variables have more explanatory power in the VOC models than the CO model. The quantifications in this paper enable calculation of expected exposure differences among travel paths for planning and routing applications. The findings also have policy and design implications to reduce bicyclists’ exposure. Separation between bicyclists and motor vehicle traffic is a necessary but not sufficient condition to reduce exposure concentrations; off-street paths are not always low-exposure facilities.     

Fatigue in transport: a review of exposure,risks, checks and controls*

Human fatigue continues to threaten safe transport. There are claims that employers of operators should do more to mitigate the risks, and several regulators are promoting fatigue-risk management in the context of safety management systems (SMS). The current paper reviews fatigue-related risk and exposure factors and control measures for operators of land- and sea-based transport forms. Our review identifies 13 types of measures for the monitoring or control of fatigue risks: optimal staffing; optimal schedule design; optimisation of breaks/naps; monitoring of actual hours worked; optimisation of work content; monitoring and feedback of actual sleep; health screening and treatment; promotion of recovery from work; fitness-for-duty testing; monitoring of fatigue symptoms while operating; control of fatigue while operating; performance monitoring and assistance; and fatigue-proofing. We also identify two systemic measures needed to anchor risk mitigation in SMS: organisational learning and training/other. By structuring monitoring and control measures along Dawson and McCulloch’s [Managing fatigue: It’s about sleep. Sleep Medicine Reviews, 9(5), 365–380] fatigue-risk trajectory, a framework is obtained that acts as a guide for fatigue-risk management by transport employers. To inform transport managers further, evaluations are needed of the effectiveness of individual control measures as well as whole fatigue-risk management interventions.     

Reducing pedestrian exposure to environmental pollutants: A combined noise exposure and air quality analysis approach

This study offers a combined analysis of pedestrian exposure to noise and air pollution within a specific urban setting in Dublin, Ireland. The impact of a recent boardwalk development on reducing pedestrian exposure to air and noise pollution is examined while modelling experiments are undertaken to explore the possibility of achieving further reductions in pollutant exposure through better urban design and planning. The results show that the boardwalk has reduced pedestrian exposure to air and noise pollution and that further reductions may be achieved by more strict segregation of pedestrian and road traffic in urban areas.     

Pricing local emission exposure of road traffic: An agent-based approach

This paper proposes a new approach to iteratively calculate local air pollution exposure tolls in large-scale urban settings by taking the exposure times and locations of individuals into consideration. It explicitly avoids detailed air pollution concentration calculations and is therefore characterized by little data requirements, reasonable computation times for iterative calculations, and open-source compatibility. In a first step, the paper shows how to derive time-dependent vehicle-specific exposure tolls in an agent-based model. It closes the circle from the polluting entity, to the receiving entity, to damage costs, to tolls, and back to the behavioral change of the polluting entity. In a second step, the approach is applied to a large-scale real-world scenario of the Munich metropolitan area in Germany. Changes in emission levels, exposure costs, and user benefits are calculated. These figures are compared to a flat emission toll, and to a regulatory measure (a speed reduction in the inner city), respectively. The results indicate that the flat emission toll reduces overall emissions more significantly than the exposure toll, but its exposure cost reductions are rather small. For the exposure toll, overall emissions increase for freight traffic which implies a potential conflict between pricing schemes to optimize local emission exposure and others to abate climate change. Regarding the mitigation of exposure costs caused by urban travelers, the regulatory measure is found to be an effective strategy, but it implies losses in user benefits.     

Population exposure to ultrafine particles: Size-resolved and real-time models for highways

Prior research on ultrafine particles (UFP) emphasizes that concentrations are especially high on-highway, and that time on highways contribute disproportionately to total daily exposures. This study estimates individual and population exposure to ultra-fine particles in the Minneapolis – St. Paul (Twin Cities) metropolitan area, Minnesota. Our approach combines a real-time model of on-highway size-resolved UFP concentrations (32 bins, 5.5–600 nm); individual travel patterns, derived from GPS travel trajectories collected in 144 individual vehicles (123 h at locations with UFP estimates among 624 vehicle-hours of travel); and, loop-detector data, indicating real-time traffic conditions throughout the study area. The results provide size-resolved spatial and temporal patterns of exposure to UFP among freeway users. On-highway exposures demonstrate significant variability among users, with highest concentrations during commuting peaks and near highway interchanges. Findings from this paper could inform future epidemiological studies in on-road exposure to UFP by linking personal exposures to traffic conditions.     

Unifying access

Since Hansen’s seminal 1959 paper, measures of access have evolved with technology and through practical applications. The myriad of distinct but familially related access measures created many more options to measure places, but has sown needless confusion. This paper systematically reviews measures of access across disciplines. We categorize measures of access, covering both mainstream and innovative but less widely-used techniques; each access measure (topological, contiguous, cumulative opportunities, utility, flow-based measures) is separated into Primal and Dual measure, based on whether accessibility is represented by the level of reachable opportunities or by the travel impedance. We show access measures are unified by the same intrinsic structure consisting of travel impedance and the opportunities reachable, and that access measured by different methods are equivalent under specific assumptions on travel impedance, and the accounting of relevant opportunities. This paper overviews the use of access measures from the existing literature, and clarifies measures of access, which should help users in the selection and appropriate use of access measures for the relevant context.     

Investigation on lowering commuters’ in-cabin exposure to ultrafine particles

To determine ways to reduce commuters’ ultrafine particle exposure, factors such as ventilation condition, mechanical airflow rate, driving speed, cabin air filter quality, and cabin air filter use are examined. The results show that the in-cabin to on-roadway ratio is reduced by 20% when the fan is set to recirculation-on versus when set to recirculation-off because fewer ultrafine particles are exchanged between the inside and outside of the cabin. Also, when the fan is set to recirculation-off, the ratio is reduced by 40% at lower mechanical airflow rates. The thickest cabin air filter resulted in a 30% in-cabin to on-roadway ratio decrease compared with the thinnest. Thus, driving conditions with the least UFP in-cabin to on-roadway ratio is when a vehicle is operating with a high efficiency cabin filter, the ventilation set to fan-on and recycling is recirculation on, and at a high ventilation airflow rate. Furthermore, recirculating in-cabin air through a high efficiency particulate air filter was found to significantly reduce in-cabin UFP exposure.     

Is in-cabin exposure to carbon monoxide and fine particulate matter amplified by the vehicle’s self-pollution potential? Quantifying the rate of exhaust intrusion

In-cabin exposure has increased in recent years due to longer commute and/or prolonged times in cars. The intrusion of the vehicle’s own exhaust into the passenger’s compartment has been recognized as a process that amplifies in-cabin passenger exposure. Quantifying its contribution is hampered by uncertainties associated with its measurement method such as trace tests and the lack of data regarding certain critical physical parameters, particularly those pertaining to air exchange rate (AER) and particulate matter deposition rate (DR). In this study, we present a hybrid methodology combining field measurements with a single-zone mass balance to estimate these parameters as well as the source term that represents vehicle self-pollution. In- and out-vehicle carbon monoxide (CO) and fine particulate matter (PM_2.5) were monitored concurrently in test vehicles under idle and moving conditions using several common ventilation modes. In addition to defining a hybrid methodology to characterize the underlying physical parameters, this study found that vehicle self-pollution can account for approximately 15 and 30% of CO and PM_2.5 exposure experienced by vehicle occupants respectively. Vehicle self-exhaust intrusion may constitute a significant PM exposure route for vehicle-based occupations or commuters with prolonged time in vehicles.     

Evaluation of total risk exposure and insurance premiums in the maritime industry

The empirical evaluation of maritime risk exposure is based on the monetary value at risk (MVR) that incorporates individual safety quality data of about 130,000 vessels, insurable values related to various potential damages, and proxies for fractions of values lost at incidents. MVR provides a tool to enhance strategic planning of maritime administrations and insurance providers, which is illustrated by a high level comparison of annual risk exposure with insurance premiums for 2010–2014. The analysis reveals a global annual insurable value of 30.6 trillion USD with associated annual MVR of 38.8 billion USD for very serious and serious incidents. Although oil tankers show the highest risk exposure (1.75 million USD per tanker per year), safety qualities are found to be best for this ship type (1.4% annual incident risk) and worst for container vessels (2.8%). Annual growth rates in total risk exposure are mostly positive with highest value for dry bulk carriers (27.8%), whereas risk exposure tends to decline for pollution of oil tankers (−2.0%) and passenger vessels (−11.3%), and for loss of life of oil tankers (−1.9%) and dry bulk carriers (−1.4%). Comparison across administrative dimensions reveals that most risk exposure lies with old open registries and with beneficial owners and the Document of Compliance companies located in high income countries. Comparison with global insurance premiums suggests reasonably adequate coverage of maritime risks (excluding cargo) with under-insurance of risk by around 5% (about 1 billion USD per year), with some uncertainties remaining for actual loss fractions of the involved damages.     

A new approach for evaluating regional exposure to particulate matter emissions from motor vehicles

Exposure to fine particulate matter from vehicle exhaust is associated with increased health risk. This study develops a new approach for creating spatially detailed regional maps of fine particulate matter concentration from vehicle exhaust using a dispersion model to better evaluate these risks. The spatial extent, diurnal, and seasonal patterns of concentration fields across Los Angeles County, California are evaluated and population exposure and exposure equity by race and income are investigated. The results demonstrate how this modeling approach can create new knowledge about vehicle emissions exposure. This approach also provides a method for proactively screening out regional plans, or specific projects within these plans, that are likely to cause air quality concerns. A proactive and regional air quality assessment can identify potential problems earlier in the planning process and a wider range of solutions, saving time, money and protecting public health. The detailed concentration maps can also be used to improve the siting of regulatory air quality monitors and provide more accurate exposure data for epidemiology studies.     

Control of traffic in residential neighborhoods: Some considerations for implementation

The effect of motor vehicles upon older neighborhoods has received increasing attention as residents of these areas seek to preserve the quality of life in their neighborhoods. In order to reduce through traffic in residential neighborhoods, numerous techniques have been developed, ranging from turn prohibitions to physical barriers. Since these measures have negative impacts on previous users of the streets, there has been substantial opposition to them. This paper reviews the major areas of conflict as revealed through court challenges.Nine court cases were identified by the researchers. In four, the court decision supported the control measures; in five, the courts decided against the actions. Six of the nine cases are reviewed in this paper. Major legal issues which are identified include the appropriate use of municipal police power, reasonableness in the exercise of police power, the integration of control measures into an overall transportation plan, appropriate consideration of emergency vehicle needs and the rights of access to property, and public participation in the decision. The authors conclude that properly planned and executed diversion strategies can be implemented and can withstand challenges by negatively affected parties.The opinions, findings, and conclusions expressed or implied in this paper are those of the authors only. They are not necessarily those of the Federal Highway Administration.     

Individual exposure to traffic related air pollution across land-use clusters

In this study, we estimated the transportation-related emissions of nitrogen oxides (NO_x) at an individual level for a sample of the Montreal population. Using linear regression, we quantified the associations between NO_x emissions and selected individual attributes. We then investigated the relationship between individual emissions of NO_x and exposure to nitrogen dioxide (NO₂) concentrations derived from a land-use regression model. Factor analysis and clustering of land-uses were used to test the relationships between emissions and exposures in different Montreal areas. We observed that the emissions generated per individual are positively associated with vehicle ownership, gender, and employment status. We also noted that individuals who live in the suburbs or in peripheral areas generate higher emissions of NO_x but are exposed to lower NO₂ concentrations at home and throughout their daily activities. Finally, we observed that for most individuals, NO₂ exposures based on daily activity locations were often slightly more elevated than NO₂ concentrations at the home location. We estimated that between 20% and 45% of individuals experience a daily exposure that is largely different from the concentration at their home location. Our findings are relevant to the evaluation of equity in the generation of transport emissions and exposure to traffic-related air pollution. We also shed light on the effect of accounting for daily activities when estimating air pollution exposure.     

A multi-layered risk exposure assessment approach for the shipping industry

Maritime administration and coastal states have become more aware of the need to enhance risk mitigation strategies primarily due to increased worldwide shipping activities, changing safety qualities of the world fleet and limited resources to deploy mitigation strategies. This paper introduces an innovative multi-layered framework to assess, predict and mitigate potential harm. The proposed approach addresses known restrictions of risk assessments in shipping. These restrictions are the lack of scalability to apply risk assessments over large areas using an automated routine, the absence of recognizing that the world fleet is heterogeneous, the lack of integrating location specific environmental conditions such as wind, currents or waves and most importantly, the lack of recognizing the uncertainties associated with each factor especially for predictions. The proposed framework is based on the idea of integrating various layers representing the most important factors that can influence risk in order to estimate and predict risk exposure for a given area. As proof of concept of the underlying ideas, the outcome of a pilot project with the Australian Maritime Safety Authority is presented which demonstrates the integration of the first two layers and is based on a unique and comprehensive combination of data. The results of selected endpoints of risk exposure compare well with observations. The article also discusses the integration of the remaining layers including the recognition and addition of uncertainties in the future.     

Access: The transport-land use economic link

The notion of access has evolved from a physical measure of trip interaction to a more economic concept associated with transport benefits. This paper follows the economic interpretation forward in order to understand the potentiality of access as a consistent economic link between the land use system and the transport system. Consistency is achieved in an economic approach based upon the argument that trips are made only if the benefit derived from making contact with other activities exceeds the transport generalized cost. This framework provides economic measures of access, as evidence of impact on origin and destination of trips, which can be calculated from the analysis of the transport system in some relevant cases. This paper analyses how to calculate measures of access from transport demand models and how to allocate transport benefits to the origin and destination activities. Finally, it describes the use of herein proposed access measures in land use-transport interaction modelling.