Gudmundur F. Ulfarsson

Microsimulation of urban development and location choices : design and implementation of UrbanSim

UrbanSim is a new urban simulation model, developed over the past several years, which is now operational in three urban areas in the United States. The model system is designed to address emerging needs to better coordinate transportation and land use planning as a result of recognition of the strong interactions between land use and transportation, increasing pressure from federal transportation and environmental legislation, and growing adoption of state growth management programs. The model system is implemented as a set of interacting model components that represent the major actors and choices in the urban system, including household moving and residential location, business choices of employment location, and developer choices of locations and types of real estate development, all subject to the influence of governmental transportation and land use policy scenarios. The model design is unusual in the degree of disaggregation of space, time, and agents, and in the adoption of a dynamic disequilibrium approach. The objective of this paper is to describe the entire system at a sufficient level of detail to convey the key specification and design choices made in implementing the system.

Differences in male and female injury severities in sport-utility vehicle, minivan, pickup and passenger car accidents

This research explores differences in injury severity between male and female drivers in single and two-vehicle accidents involving passenger cars, pickups, sport-utility vehicles (SUVs), and minivans. Separate multivariate multinomial logit models of injury severity are estimated for male and female drivers. The models predict the probability of four injury severity outcomes: no injury (property damage only), possible injury, evident injury, and fatal/disabling injury. The models are conditioned on driver gender and the number and type of vehicles involved in the accident. The conditional structure avoids bias caused by men and womens different reporting rates, choices of vehicle type, and their different rates of participation as drivers, which would affect a joint model of all crashes. We found variables that have opposite effects for the genders, such as striking a barrier or a guardrail, and crashing while starting a vehicle. The results suggest there are important behavioral and physiological differences between male and female drivers that must be explored further and addressed in vehicle and roadway design.

Urban sprawl and the cost of public services

One of the principle criticisms of urban sprawl is that it undermines the cost-effective provision of public services. In this paper the authors examine whether or not this is true through an exploratory analysis of the influence that alternative development patterns have on twelve measures of public expenditure: total direct, capital facilities, roadways, other transportation, sewerage, trash collection, housing and community development, police protection, fire protection, parks, education, and libraries. The objectives of the analysis are threefold. First, the authors, through a background discussion, provide a brief overview of previous research on the relationship between urban development patterns and the cost of public services. Second, through empirical analysis, they examine how the character of urban development affects per capita public outlays in a cross-section of 283 metropolitan counties during the 1982–92 time period. A separate equation is estimated for each measure of expenditure, providing substantive evidence on how density, the spatial extent of urbanized land area, property value, and political fragmentation affect the cost of services. Finally, the authors use the results of the empirical analysis to develop a set of policy recommendations and directions for future research.

Fragmentation and Sprawl: Evidence from Interregional Analysis

Recent years have witnessed widespread expansion of state and regional planning programs in the United States. A major purpose of these efforts is to reduce urban sprawl—low density, discontinuous, suburban–style development, often characterized as the result of rapid, unplanned, and/or uncoordinated growth— by promoting jurisdictional cooperation and regulatory consistency across metropolitan areas. This paper evaluates the efficacy of this approach by examining the relationship between governmental fragmentation and several measurable outcomes of urban development: density, urbanized land area, property value, and public expenditures on infrastructure. The four dimensions are modeled in a simultaneous equations framework, providing substantive evidence on how fragmentation and other exogenous factors affect metropolitan growth patterns. Fragmentation is associated with lower densities and higher property values, but has no direct effect on public service expenditures; less fragmented metropolitan areas occupy greater amounts of land due to the extensive annexation needed to bring new development under the control of a central municipality. The findings of the analysis lend support to state and regional planning efforts aimed at increasing cooperation among local governments, but also suggest that further research is needed in order to evaluate whether or not they produce their intended effects.

Introduction to Urban Simulation: Design and Development of Operational Models

This chapter has sought to explain the context, policy applications, and major design choices in the process of developing an operational urban simulation model, with specific reference to UrbanSim as a case study. It has been argued that careful design at each stage of the process is needed to make the model sensitive to the policies of principal concern, to make the data and computational requirements manageable, to make the model usable by staff and other users with appropriate levels of training, and to fit into the operational practices of the relevant organizations. To be useful (relevant) in the policy process, model design should carefully integrate the elements discussed in the chapter into a design that fits well into a specific institutional and political context, and evolve to adapt to changing conditions. This introduction to the design process sets the stage for more in-depth discussion of specification and operational issues in model use. The UrbanSim system is being further developed to adapt to varying data availability, different factors influencing agent choices in locations ranging from newer and rapidly growing US metropolitan areas in other parts of the world. Considerable effort is now being devoted to developing environmental components of the system such as land cover change, and to developing a robust interface and tools for visualization and evaluation of policy scenarios.

Age and pedestrian injury severity in motor-vehicle crashes : A heteroskedastic logit analysis

This research explores the injury severity of pedestrians in motor-vehicle crashes. It is hypothesized that the variance of unobserved pedestrian characteristics increases with age. In response, a heteroskedastic generalized extreme value model is used. The analysis links explanatory factors with four injury outcomes: fatal, incapacitating, non-incapacitating, and possible or no injury. Police-reported crash data between 1997 and 2000 from North Carolina, USA, are used. The results show that pedestrian age induces heteroskedasticity which affects the probability of fatal injury. The effect grows more pronounced with increasing age past 65. The heteroskedastic model provides a better fit than the multinomial logit model. Notable factors increasing the probability of fatal pedestrian injury: increasing pedestrian age, male driver, intoxicated driver (2.7 times greater probability of fatality), traffic sign, commercial area, darkness with or without streetlights (2-4 times greater probability of fatality), sport-utility vehicle, truck, freeway, two-way divided roadway, speeding-involved, off roadway, motorist turning or backing, both driver and pedestrian at fault, and pedestrian only at fault. Conversely, the probability of a fatal injury decreased: with increasing driver age, during the PM traffic peak, with traffic signal control, in inclement weather, on a curved roadway, at a crosswalk, and when walking along roadway.

Modeling crashes involving pedestrians and motorized traffic

This paper presents an empirical inquiry into the predictive modeling of crashes involving pedestrians and motorized traffic on roadways. Empirical models based on the negative binomial distribution and mixing distributions, such as the zero-inflated Poisson distribution, are presented and discussed in terms of their applicability to pedestrian crash phenomena. Key modeling issues relating to the presence of excess zeros as well as unobserved heterogeneity in pedestrian crash distributions are addressed. The empirical results show that zero-inflated count distributions, such as the zero-inflated Poisson, are promising methodologies for providing explanatory insights into the causality behind pedestrian-traffic crashes.

Driver-injury severity in single-vehicle crashes in California: A mixed logit analysis of heterogeneity due to age and gender

This research develops a mixed logit model of driver-injury severity in single-vehicle crashes in California. The research especially considers the heterogeneous effects of age and gender. Older drivers (65+ years old) were found to have a random parameter with about half the population having a higher probability of a fatal injury given a crash than the comparison group of 25-64 year olds with all other factors than age kept constant. The other half of the 65+ population had a lower probability of fatal injury. Heterogeneity was also noted in vehicle age, but related to the gender of the driver, with males linked to, on average, a higher probability of fatal injury in a newer vehicle compared with females, all other factors kept constant. These effects lend support to the use of mixed logit models in injury severity research and show age and gender based population heterogeneity. Several other factors were found to significantly increase the probability of fatal injury for drivers in single-vehicle crashes, most notably: male driver, drunk driving, unsafe speed, older driver (65+) driving an older vehicle, and darkness without streetlights.

TRAVEL MODE CHOICE OF THE ELDERLY: EFFECTS OF PERSONAL, HOUSEHOLD, NEIGHBORHOOD, AND TRIP CHARACTERISTICS

The travel patterns and travel mode choice of the elderly are analyzed. The elderly are here defined as those who are both 65 or older and retired. A rapid increase in the older population and their proportion in society has tremendous implications for transportation planning and the policy arena. Previous studies on mode choice have been largely focused on working-age people, and existing studies on the travel mode choice of the elderly are limited to descriptive analyses. A systematic analysis is presented of the mode choice of the elderly and how it relates to activity purpose. It is found that neighborhood and trip characteristics, as well as personal and household characteristics, are associated with the mode choice of this group. For example, the elderly are more likely to use transit if they live within five blocks of a bus stop, and they are more likely to share a ride with others when chaining trips, doing errands, or going to a medical appointment and are less likely to use transit when going shopping or doing errands. The elderly prefer walking when going on recreational or personal trips. Those with a higher income are more likely to drive or carpool. The results shed light on the mode choice of the elderly and contribute to the development of a transportation policy framework that considers the elderly. The results suggest that transportation strategies must move beyond private automobiles to prepare adequately for the increasing number of the elderly in society and their mobility needs.

Random parameter models of interstate crash frequencies by severity, number of vehicles involved, collision and location type

A nine-year (1999-2007) continuous panel of crash histories on interstates in Washington State, USA, was used to estimate random parameter negative binomial (RPNB) models for various aggregations of crashes. A total of 21 different models were assessed in terms of four ways to aggregate crashes, by: (a) severity, (b) number of vehicles involved, (c) crash type, and by (d) location characteristics. The models within these aggregations include specifications for all severities (property damage only, possible injury, evident injury, disabling injury, and fatality), number of vehicles involved (one-vehicle to five-or-more-vehicle), crash type (sideswipe, same direction, overturn, head-on, fixed object, rear-end, and other), and location types (urban interchange, rural interchange, urban non-interchange, rural non-interchange). A total of 1153 directional road segments comprising of the seven Washington State interstates were analyzed, yielding statistical models of crash frequency based on 10,377 observations. These results suggest that in general there was a significant improvement in log-likelihood when using RPNB compared to a fixed parameter negative binomial baseline model. Heterogeneity effects are most noticeable for lighting type, road curvature, and traffic volume (ADT). Median lighting or right-side lighting are linked to increased crash frequencies in many models for more than half of the road segments compared to both-sides lighting. Both-sides lighting thereby appears to generally lead to a safety improvement. Traffic volume has a random parameter but the effect is always toward increasing crash frequencies as expected. However that the effect is random shows that the effect of traffic volume on crash frequency is complex and varies by road segment. The number of lanes has a random parameter effect only in the interchange type models. The results show that road segment-specific insights into crash frequency occurrence can lead to improved design policy and project prioritization.