Pedestrian Exposure Research Articles

The importance of measuring ultrafine particles in urban air quality monitoring in small cities

The air quality monitoring is based on the determination of some gaseous pollutants and PM10 and PM2.5. Recent studies have reported the importance of the determination aerosol fraction below 1 µm both for the dynamic of the airborne and for the public health issue. This paper would like to investigate the importance of this fraction in the air quality monitoring. Further, a particular focus will be devoted the role of the Ultrafine Particles, i.e. particles below 100 nm, in the aerosol formation and in the human exposure. Two case studies will be presented and discussed on how the submicron particles can be determined and interpreted their role. In the first case, the measurements will be performed in downtown Rieti, city located in central Italy, 100 km North from Rome, with the scope to draw the behavior in relationship to the emission flexes. In the second scenario, the personal exposure of pedestrians will be investigated in Venafro, a small city located 150 km South-East Rome, by means of measuring PMx, total submicron fraction, different aerosol dimensional sizes in the range 5-360 nm along with the total Volatile Compounds. The different sources and contributions affecting the aerosol levels in the two areas will be investigated and extensively discussed as well as the role of the such particles in the aerosols science.

Representativeness and variability of PM2.5 mass concentrations and black carbon near traffic and urban background monitoring stations/Repräsentativität und Variabilität von PM2.5-Massenkonzentrationen und schwarzem Kohlenstoff in der Nähe von Verkehrs- und städtischen Luftgütemessstationen.

Mobile measurements of PM2.5 and black carbon (BC) mass concentrations were performed near regular monitoring stations in order to gain deeper understanding of the drivers of pedestrian exposure to traffic-related air pollution. The following investigations have been done: A) Yearlong measurements in an area around a street canyon approximately 3 km airline distance from the city center of Leipzig showed that the spatial distributions of both pollutants are elevated during wintertime. The patterns of the BC mass concentration, however, consistently showed a strong influence from traffic emissions in the street, while the PM2.5 mass concentration was more dependent on the regional background and less on urban sources. B) Measurements in the city of Dresden near two regular monitoring stations, one at a roadside and one in urban background areas revealed differences between the two in terms of the BC mass concentrations, with slightly higher concentrations at the traffic area. However, no significant differences between the spatial distributions of PM2.5 mass concentrations were observed. The background measurements of the PM2.5 mass concentrations seem to be generally representative for the residential area. C) Measurements near a regular monitoring station located at a junction of the inner-city ring road of Leipzig showed that it is representative of its immediate vicinity in terms of BC mass concentrations. However, the PM2.5 mass concentration varied by a factor 2, reaching the highest levels near in the central tram station about 200 m away. The central tram station seems to significantly influence the PM2.5 mass concentration. These results of the three studies provide a better understanding of the variability of these two parameters in urban areas in Leipzig and Dresden, helping local policy makers to interpret better the measured air pollution.

Mitigation impact of roadside trees on fine particle pollution

Fine particulate matter (PM2.5) is an important air pollutant due to its adverse health effects. Vehicle emissions make a large contribution to particle concentrations in urban areas. Exposure to particles especially near roadways increases the risk of public health problems. Planting vegetation might be used to capture the fine particles at the roadside, which can lower the health risks for the urban population. Istanbul is the most populous city in Turkey, where the number of non-electric cars is increasing rapidly, resulting in decreasing air quality, especially at the roadsides. Recent studies show that cardiovascular, respiratory and total non-accidental mortality is increasing with short-term exposure to outdoor air pollution in Istanbul. In this study, roadside trees were investigated for the mitigation effect on vehicle-related PM2.5 and heavy metal (HM). Cupressus sempervirens (Mediterranean Cypress trees) were planted in three different cases (i.e., no trees-C1, trees with gaps-C2 and thick trees with no gaps-C3) at the study site. Location of the site is on a dense-traffic roadside in Istanbul, where thousands of people are living, working and walking through two sides of this road. PM2.5 samples and tree leaves were examined in the performed experiments. C2 and C3 showed the importance of roadside tree plantation by reducing the exposure to significantly low levels. Roadside PM2.5 concentrations were reduced by 17% in C3, equivalent to urban background levels in the city. Maximum removal of HMs is observed in nickel from 26.4 ± 7.8 to 7.5 ± 2.4 μg m−3. Pedestrian exposure is calculated with the measured data in three experiments and exposure is significantly reduced (e.g., >50% for cadmium and lead exposure) in experiment C3. In conclusion, three experiments showed that Mediterranean Cypress trees significantly decreased particle pollution at roadsides in Istanbul.

Evaluation of surrogate measures for pedestrian trips at intersections and crash modeling

Pedestrians are considered the most vulnerable road users who are directly exposed to traffic crashes. With a view to addressing the growing concern of pedestrian safety, Federal and local governments aim at reducing pedestrian-involved crashes. Nevertheless, pedestrian volume data are rarely available even though they among the most important factors to identify pedestrian safety. Thus, this study aims at identifying surrogate measures for pedestrian exposure at intersections. A two-step process is implemented: the first step is the development of Tobit and generalized linear models for predicting pedestrian trips (i.e., exposure models). In the second step, negative binomial and zero inflated negative binomial models were developed for pedestrian crashes using the predicted pedestrian trips. The results indicate that among various exposure models the Tobit model performs the best in describing pedestrian exposure. The identified exposure-relevant factors are the presence of schools, car-ownership, pavement condition, sidewalk width, bus ridership, intersection control type and presence of sidewalk barrier. It was also found that the negative binomial model with the predicted pedestrian trips and that with the observed pedestrian trips perform equally well for estimating pedestrian crashes. Also, the difference between the observed and the predicted pedestrian trips does not appear as statistically significant, according to the results of the t-test and Wilcoxon signed-rank test. It is expected that the methodologies using predicted pedestrian trips or directly including pedestrian surrogate exposure variables can estimate safety performance functions for pedestrian crashes even though when pedestrian trip data is not available.

A parametric study of the effect of roof height and morphology on air pollution dispersion in street canyons

We investigate the effect of conventional pitched roofs on ventilation and pollution in street canyons using Computational Fluid Dynamics and a parametric approach. We studied parallel street canyons with several street morphologies, created by assigning a set of streets with pitched roofs, and varying their pitch and arrangement for three different height-to-width aspect ratios. The distribution of flow properties and pollution concentrations within the street canyons are examined and the effect of different parameter combinations is assessed. We find the relationship between these properties and the street morphology to be complex and case specific.For most morphologies, the pitched roofs lead to higher average pollution concentrations, and in some cases to pollution hotspots near emission sources especially on the leeward side. The pitched roofs are rarely beneficial to ventilation of the street canyons, but a few roof arrangements lead to reduced concentrations on the windward side. Roof slope is shown to significantly relate to both average pollution concentrations and their distribution inside the street; in some street geometries more than others. The results have implications for pedestrian and residential pollution exposure, and for conservation of building facades on historical buildings.

Investigating traffic-related PM exposure on and under pedestrian bridges: A case study in Xi'an, China

We measured particulate matter concentrations (PMCs), including PM10, PM2.5, and PM1.0 fractions, on and under pedestrian bridges over two different types of roads: an urban expressway and an arterial road. The objectives of the study were to 1) assess the variability of PMCs measured at pedestrian bridges, 2) identify best-fit probability distribution curves of different measures of PMCs, and 3) quantify pedestrian exposure (by respiratory deposition dose (RDD) rate). Results showed that the average on-bridge PM concentrations were significantly higher than the under-bridge values over the urban expressway, although no similar trend observed over the arterial road. More specifically, average PM1.0 concentration on the bridge was 1.29 times of that under the bridge over the urban expressway. Gaussian distribution “best” fit the 30s average PMCs for PM10 on and under the pedestrian bridge over the urban expressway, and LogNormal distribution “best” fit the PMCs for PM10 on and under the bridge for the arterial road. The average RDD rates for PM10 (143.85 μg h−1), PM2.5 (9.41 μg h−1), and PM1.0 (3.78 μg h−1) on the bridge over the urban expressway (OBUE) were higher by 47%, 41%, and 11%, respectively, than those on the bridge over the arterial road (OBAR). While only minor differences were noticed in the average RDDs of PM between on and under the pedestrian bridge over the arterial road, a significant difference in the average RDD rate was found between on and under pedestrian bridges over the urban expressway.

Investigation into pedestrian exposure to traffic PM around grade separations: a case study in Xi’an, China

To investigate the influence of grade separations on the concentration dynamics of particulate matter (PM) and pedestrian PM exposure rate, PM mass concentrations (PMCs) at and around a typical grade separation were measured. Using a statistical fitting method, the horizontal variation and frequency distributions for PMCs at the entrance and exit of a grade separation were investigated. The pedestrian exposure around the grade separation was quantified in terms of respiratory deposition dose (RDD) rates. The results of the case study showed that the average mass concentrations of PM10, PM2.5, and PM1 at the exit of the underpass were found to be about 19, 9, and 4% higher than those at the entrance, and the concentrations of PM10, PM2.5, and PM1 in the underpass were higher compared with those on the overpass. The average mass concentrations of PM10 (136 μg m−3), PM2.5 (67 μg m−3), and PM1 (44 μg m−3) in the underpass exceeded those on the overpass by about 14, 8, and 7%, respectively. Further analysis of the underpass revealed that all three types of PMCs decayed exponentially with increasing distance from the exit. However, for the entrance, as the distance from the entrance increased, PMCs began to drop slightly, and then rose to the maximum near the ramp. Based on the frequency histograms and corresponding fitted curves at the entrance and exit of the underpass, the rate of violation of ambient PM concentrations was assessed. The total respiratory deposition dose (RDD) rates of PM10, PM2.5, and PM1 around the grade separation were roughly 3.4, 2.8, and 2.5 times higher than those of the background, respectively. The findings of this study are a step toward understanding more environmentally friendly grade-separation design strategies.

Numerical investigation to examine two methods of passive control in urban street canyon using CFD: Comparison between crossing under building and solid barriers lbw

Different passive control methods are discussed in this paper with the purpose of improved the quality of the air and dispersed the pollution outside the urban canyon road. Numerical investigation model is used in this paper, to examine two methods of passive control within a crossing under building and Low Boundary Wall in center of road for reducing air pollution concentration using Reynolds-averaged Navier–Stokes equations and the k-Epsilon turbulence model as close of the equation system. The results of this investigation show that a low boundary wall located at the central median of the street canyon creates a significant reduction in pedestrian exposure, relative to the same canyon with no wall. The magnitude of the exposure reduction was also found to vary according to the numbers of the crossing under building in the street canyon geometry. The values of the concentration normalized is decreased in the critical region were located in the centerline of the street canyon. Keywords : Passive Methods, Barriers, Street Canyon, Pollutant Dispersion, Numerical Simulation.

Redefining Safe Streets through a New Child Pedestrian Demand/Exposure Model ( breakout presentation )

Background Child pedestrians are one of the most vulnerable road user types due to physical and developmental disadvantages and a lack of a protective covering from a vehicle. This combination of vulnerabilities results in poor safety outcomes. However, there are two types of locations in which child pedestrians are unsafe: (1) those locations that are unsafe as evidenced by a prevalence of crashes and (2) those locations that are so unsafe that there are no pedestrians using them, and therefore no crashes. In order to understand if an area is truly safe, or if it is so unsafe that it is being underutilized, we need to know where trips are occurring and also where they are being held back. Aim The purpose of this work is to create a model that accounts for both child pedestrian exposure and child pedestrian demand that remains latent. Currently, a lack of adequate pedestrian exposure modeling precludes our ability to improve safety outcomes, because a problem that cannot be correctly identified and defined cannot be solved. Method The multilevel spatial model utilizes population as a base, socioeconomics, demographics, crime, and land use as a secondary-tier, and pedestrian infrastructure as a third-tier. This spatial syntax enhancement is implemented through GIS while being checked and calibrated against real-world safety conditions. Once calibrated with child pedestrian crashes, injuries, and fatalities, this tool becomes a powerful predictor of poor safety outcomes and a holistic identifier of problem areas in our cities. Results By accounting for both exposure and latent demand, we can now successfully determine if a location is truly safe for pedestrians, truly unsafe, or so unsafe that it appears to be safe. Conclusions Practitioners and researchers alike can use this tool to enhance safety for varying populations. By better understanding where safety issues persist in our urban transportation systems, we can then work towards solving those issues, thereby enhancing safety for some of the most vulnerable road users.

Where to locate transit stops: Cross-intersection profiles of ultrafine particles and implications for pedestrian exposure.

Epidemiological studies have shown that exposure to traffic-related pollutants increases incidence of adverse health outcomes. Transit users in cities across the globe commonly spend 15-45min or more waiting at transit stops each day, often at locations with high levels of pollution from traffic. Here, we investigate the characteristics of concentration profiles of ultrafine particles (UFP) with 5m spatial resolution across intersections, to determine the best place to site transit stops to minimize exposures. Cross-intersection UFP profiles were derived from 1744 profiles covering 90m before and after each intersection center with a mobile monitoring platform. Measurements were made at 10 signalized intersections located at six urban sites, each with a distinct built environment, during both mornings and afternoons. Measurements were made within 1.5m of the sidewalk and approximately at breathing height (1.5m above ground level) to approximate sidewalk exposures. UFP profiles were strongly influenced by high emissions from vehicle stops and accelerations, and peaked within 30m of intersection centers; from there concentrations decreased sharply with distance. Peak concentrations averaged about 90% higher than the minima along the block. They were accompanied by more frequent and larger transient concentration spikes, increasing the chance of people near the intersection being exposed to both short-term extremely high concentration spikes and higher average concentrations. The decays are somewhat larger before the intersection than after the intersection, however as siting transit stops after intersections is preferred for smooth traffic flow, we focus on after the intersection. Simple time-duration exposure calculations combined with breathing rates suggest moving a bus stop from 20 to 40-50m after the intersection can reduce transit-users' exposure levels to total UFP substantially, in proportion to the reciprocal of the magnitude of elevation at the intersection.

Fine-Scale Spatial Variability of Pedestrian-Level Particulate Matters in Compact Urban Commercial Districts in Hong Kong.

Particulate matters (PM) at the pedestrian level significantly raises the health impacts in the compact urban environment of Hong Kong. A detailed investigation of the fine-scale spatial variation of pedestrian-level PM is necessary to assess the health risk to pedestrians in the outdoor environment. However, the collection of PM data is difficult in the compact urban environment of Hong Kong due to the limited amount of roadside monitoring stations and the complicated urban context. In this study, we measured the fine-scale spatial variability of the PM in three of the most representative commercial districts of Hong Kong using a backpack outdoor environmental measuring unit. Based on the measurement data, 13 types of geospatial interpolation methods were examined for the spatial mapping of PM2.5 and PM10 with a group of building geometrical covariates. Geostatistical modelling was adopted as the basis of spatial interpolation of the PM. The results show that the original cokriging with the exponential kernel function provides the best performance in the PM mapping. Using the fine-scale building geometrical features as covariates slightly improves the interpolation performance. The study results also imply that the fine-scale, localized pollution emission sources heavily influence pedestrian exposure to PM.

In-vehicle and pedestrian exposure to carbon monoxide and volatile organic compounds in a mega city

This study is to determine in-vehicle and pedestrian exposure to carbon monoxide (CO) and volatile organic compounds (VOCs) in six roadways in Lagos mega city. Measurements were made twice a day for two weeks for four major modes of transportation in the city using the MultiRae ambient gas monitor. The levels of CO measured were 4.40–39.78ppm while that of VOCs were 0.00–0.39ppm. Highest average CO and VOCs concentrations were obtained inside car during morning commuting periods. These average concentrations were found to be statistically significant when compared with other three transportation modes studied. The average concentrations of the pollutants in the morning were statistically similar to average concentration in the afternoon as Student's t-test indicated no statistical significant difference (p>0.05). This study revealed that car commuters are exposed to higher concentrations of CO and VOCs than bus and BRT commuters with pedestrians having the lowest exposure to the pollutants.

Air flow and pollution in a real, heterogeneous urban street canyon: A field and laboratory study

In this work we investigate the influence of real world conditions, including heterogeneity and natural variability of background wind, on the air flow and pollutant concentrations in a heterogeneous urban street canyon using both a series of field measurements and controlled laboratory experiments. Field measurements of wind velocities and Carbon Monoxide (CO) concentrations were taken under field conditions in a heterogeneous street in a city centre at several cross-sections along the length of the street (each cross-section being of different aspect ratio). The real field background wind was in fact observed to be highly variable and thus different Intensive Observation Periods (IOPs) represented by a different mean wind velocity and different wind variability were defined. Observed pollution concentrations reveal high sensitivity to local parameters: there is a bias towards the side closer to the traffic lane; higher concentrations are found in the centre of the street as compared to cross-sections closer to the junctions; higher concentrations are found at 1.5 height from the ground than at 2.5 m height, all of which are of concern regarding pedestrian exposure to traffic-related pollution. A physical model of the same street was produced for the purpose of laboratory experiments, making some geometrical simplifications of complex volumes and extrusions. The physical model was tested in an Atmospheric Boundary Layer water channel, using simultaneously Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF), for flow visualisation as well as for quantitative measurement of concentrations and flow velocities. The wind field conditions were represented by a steady mean approach velocity in the laboratory simulation (essentially representing periods of near-zero wind variability). The laboratory investigations showed a clear sensitivity of the resulting flow field to the local geometry and substantial three-dimensional flow patterns were observed throughout the modelled street. The real-field observations and the laboratory measurements were compared. Overall, we found that lower variability in the background wind does not necessarily ensure a better agreement between the airflow velocity measured in the field and in the lab. In fact, it was observed that in certain cross sections, the airflow was more affected by the particular complex architectural features such as building extrusions and balconies, which were not represented in the simplified physical model tested in the laboratory, than by the real wind field variability. For wind speed comparisons the most favourable agreement (36.6% of the compared values were within a factor of 2) was found in the case of lowest wind variability and in the section with the most simple geometry where the physical lab model was most similar to the real street. For wind direction comparisons the most favourable agreement (45.5% of the compared values was within ±45°) was found in the case with higher wind variability but in the cross-sections with more homogeneous geometrical features. Street canyons are often simplified in research and are often modelled as homogenous symmetrical canyons under steady flow, for practical purposes; our study as a whole demonstrates that natural variability and heterogeneity play a large role in how pollution disperses throughout the street, and therefore further detail in models is vital to understand real world conditions.

Exposure to Particulate Pollution in Transportation Microenvironments in Bogotá, Colombia

Exposure to air pollutants in transportation microenvironments contributes a significant fraction to total pollutant exposure for city dwellers, particularly, in cities with mobility challenges where duration of exposure to traffic related pollutants can be considerably higher. This work assesses the factors influencing particulate matter exposure and inhaled dose in transport microenvironments in a large and rapidly growing metropolitan area. We determined the influence of transport alternative on inhaled dose by quantifying and comparing the dose of commuters in different transportation modes. The intake dose of fine particulate matter (PM2.5), equivalent black carbon (eBC), and number of sub-micron particles (Np) was measured for commuters in Bogotá, Colombia. The impact of travel mode, traffic load, and street configuration on dose and exposure were explored. Two active modes (walking and cycling) and a variety of motorized modes (bus, car, taxi, and motorcycle) were included in the study. Exposure concentrations of PM2.5, eBC, and Np were measured for commuters traveling a predefined path simultaneously using different transportation alternatives. The pollutants were measured continuously using laser based methods, aethalometers, and miniature diffusion size classifiers. Physical activity level associated to each commute alternative was determined with portable activity monitors and used to infer corresponding inhalation rates. Three different streets, all with similar length but widely different traffic composition and load were considered. Extremely high average eBC concentrations, ranging from 20 to 120 µg/m3, were observed throughout the campaign. The highest average concentrations of PM2.5, eBC, and Np were measured inside Bus Rapid Transit (BRT) system vehicles. These concentrations were significantly higher than those in any other mode studied. Pedestrians and bicycle users in an open street configuration experienced the lowest average concentrations of PM2.5 and eBC, six times lower than those in the BRT buses. However, pedestrians experienced the highest particulate matter intake dose in the road segments studied. Exposure concentration inside the fleet of diesel buses was significantly higher than the concentration exposure of pedestrians and bike users. The BRT system buses were consistently found to be the most polluted transport microenvironment among the ones considered in the study. The extremely high concentrations of eBC, as well as the eBC/PM2.5 ratio imply a large contribution from Diesel engine emissions to the fine particulate concentrations. Bogotá’s BRT system currently transports nearly 2.4 million passengers daily, suggesting that the high pollution levels inside the bus cabins can affect a substantial population.

Pedestrian exposure to traffic PM on different types of urban roads: A case study of Xi’an, China

To investigate the pedestrian exposure to fine particulate on various typical urban roadways, mass concentration of PM10, PM2.5, PM1 and particle number concentrations in the given size distribution were obtained at four types of urban roads in Xi’an City: urban expressway, arterial road, collector road, and local road. The principal component analysis (PCA) was used. Measurement and analysis results showed that the mean particle number concentration for the size range of 0.25–32μm on the urban expressway was 9%, 29% and 32% higher than those on the arterial road, the collector road and the local road, respectively. However, the mass concentration of particles, especially for PM2.5 and PM1, varied little. Traffic volumes on the urban expressway, the collector road and the local road all had important influences on PM particle-number concentration, but at different size ranges. Additionally, the results discussion indicated that PM10, PM2.5 and PM1 were generated from the same emission source(i.e. vehicles)on the urban expressway, yet on the other types of roads PM (especially PM10 and PM1) emissions were generated from different sources (i.e. vehicles, pedestrians, or road dust).

Way to Go: Identifying Routes for Walkers and Cyclists to Avoid Air Pollutants.

Way to Go: Identifying Routes for Walkers and Cyclists to Avoid Air Pollutants.

The exposure of pedestrians, drivers and road transport passengers to nitrogen dioxide

People travelling by road transport are exposed to high levels of nitrogen oxides (NOx), that are considered to be one of the primary pollutants from motor vehicles. This study examines the exposure of drivers, passengers and pedestrians to NO2 during different trip scenarios: travelling by private or public means of transport, along the major commuter routes in one of the biggest Polish agglomerations - Silesia Agglomeration, and other important communication routes in Poland, as well as during walks in both city centers and residential areas. The NO2 samples were collected in cars, trucks and buses interiors, as well as in the ambient air by passive samplers and next NO2 concentrations were analyzed by means of the spectrophotometric technique. The obtained results indicate that travelling by cars through city centers is associated with the exposure to NO2 concentrations of about 15% higher than in the case of travelling suburban routes; 33% greater than travelling by bus in urban traffic; more than app. 60% higher than in the case of travelling by bus in suburban traffic or by foot in city centers and up to 80% higher than moving on foot near little-used roads. The exposure profile of six groups of road users exposed to NO2 was therefore determined in this study. The obtained results could be used by policy makers to minimize the exposure to transportation-related pollutants concentrations and for planning far-reaching changes in the field of urban road transport.

Numerical investigations of flow and passive pollutant exposure in high-rise deep street canyons with various street aspect ratios and viaduct settings.

Vehicular pollutant exposure of residents and pedestrians in high-rise deep street canyons with viaducts and noise barriers requires special concerns because the ventilation capacity is weak and the literature reported inconsistent findings on flow patterns as aspect ratios (building height/street width, H/W) are larger than 2. By conducting computational fluid dynamics (CFD) simulations coupled with the intake fraction iF and the daily pollutant exposure Et, this paper investigates the impact of street aspect ratios, viaducts and noise barriers on the flow and vehicular passive pollutant exposure in full-scale street canyons (H/W=1-6, W=24m). iF represents the fraction of total emissions inhaled by a population (1ppm=10-6), while Et means the extent of human beings' contact with pollutants within one day. CFD methodologies of passive pollutant dispersion modeling are successfully validated by wind tunnel data in Meroney et al. (1996). As a novelty, the two-main-vortex pattern start appearing in full-scale street canyons as H/W changes from 4 to 5, however previous studies using wind-tunnel-scale models (H=6cm) reported two to five vortexes as H/W=2-5. This finding is validated by both smoke visualization in scale-model outdoor field experiments (H=1.2m, W=0.6m) and CFD simulations of Reynolds number independence. Cases with two main vortexes (H/W=5-6) experience much larger daily pollutant exposure (~103-104mg/m3/day) than those with single main vortex as H/W=1-4 (~101-102mg/m3/day). Moreover leeward-side pollutant exposures are much larger than windward-side as H/W=1-4 while oppositely as H/W=5-6. Assuming a general population density, the total iF is 485-803ppm as H/W=1, 2020-12051ppm as H/W=2-4, and 51112-794026ppm as H/W=5-6. With a single elevated pollutant source, cases with viaducts experience significantly smaller pollutant exposures than cases without viaducts. Road barriers slightly increase pollutant exposure in near-road buildings with H/W=1 while reduce a little as H/W=3 and 5. Two-source cases can experience 2.60-5.52 times pollutant exposure as great as single-source cases.

Estimating Pedestrian Exposure for Small Urban and Rural Areas

Pedestrian exposure refers to a pedestrian’s contact with vehicular traffic that can create opportunities for collisions. A myriad of metrics exists to estimate pedestrian exposure, but no consensus has been reached on what metrics should be adopted. Hence this study attempted to synthesize previous studies and recommend methods for estimating pedestrian exposure, with a focus on rural and small urban areas. Five general types of exposure metrics emerged: from area-based measures (e.g., zonal walk miles traveled), through more granular metrics at the point or segment level, to advanced metrics that utilize the behavioral attributes of walk trips (e.g., space–time prism and discrete choice). In addition, the study used a finite mixture model to estimate a household-level pedestrian exposure measure for rural and small urban settings with the use of the National Household Travel Survey 2009 data. The model accounted for household characteristics (e.g., income and vehicle ownership), regional factors, and block group level attributes (e.g., population density and land use). The results show that the finite mixture model outperformed the negative binomial and zero-inflated models. The results can be used to infer the number of walk trips at as small as the block group level or be inserted into a four-step travel demand model to create point- or segment-based measures where pedestrian network is defined.

Ballpark Method for Estimating Pedestrian and Bicyclist Exposure in Seattle, Washington

The Moving Ahead for Progress in the 21st Century Act emphasized the use of data and performance measurement to track progress toward its transportation policy and safety goals. As U.S. cities and states implement policies to eliminate traffic deaths and serious injuries, exposure data are needed to contextualize crash analyses and prioritize effective countermeasures to reduce future risk. However, comprehensive counting programs are resource intensive. Research suggests that so-called big data can supplement traditional counting programs, fill the data gap, and allow for more robust exposure modeling. This paper presents the results of an abbreviated exposure estimation process to develop ballpark pedestrian and bicycle estimates for the city of Seattle, Washington, conducted as part of a major bicycle and pedestrian safety analysis for Seattle's Vision Zero effort. This paper contributes to existing research on exposure estimation and demonstrates a case study of practice-ready bicycle and pedestrian exposure models. Because of budget and time constraints, the exposure estimates used available data sources and were based on models from earlier bicycle and pedestrian volume estimation studies. The pedestrian model (pseudo- R2 = .76) fit with published models, and the bicycle model had decent explanatory power (pseudo- R2 = .57). After Strava data were added to the bicycle model, the explanatory power rose to 62% and the model was simplified. The estimates were tested in a multivariate crash analysis and used to support countermeasure identification and project prioritization. This type of abbreviated process may be appropriate for other cities seeking to estimate exposure but without the resources for a full-scale estimation effort.