Genevieve Giuliano

INCIDENT CHARACTERISTICS, FREQUENCY, AND DURATION ON A HIGH VOLUME URBAN FREEWAY

Rapidly deteriorating travel conditions in U.S. metropolitan areas have led to renewed interest in more effectively managing nonrecurrent congestion. Effective incident management requires an understanding of incident patterns, frequency, and duration. However, such information is limited. This paper presents an analysis of incidents using data from a major Los Angeles, California freeway. Incident patterns are described, and duration is analyzed as a function of incident characteristics. Results indicate that accidents make up a very small proportion of all incidents, but account for a relatively greater share of all incident duration. Major explanatory factors of incident duration include incident type, time of day, truck involvement, and lane closures. The paper concludes with a discussion of alternative approaches to reducing the congestion impacts of incidents.

Another Look at Travel Patterns and Urban Form: The US and Great Britain

This paper explores the relationship between land-use patterns and individual mobility from a comparative international perspective. There is a vast literature on US automobile dependence. Major explanatory factors include: transport, housing, land-use and tax policy; per capita incomes; American cultural preferences; national geography; and the spatial structure of US metropolitan areas (itself a result of the first three factors). Emphasising the policy environment, many researchers have cast their analysis in comparative terms, noting the differences in automobile use between European countries and the US. It is argued that US patterns of metropolitan form, with low development densities and dispersed population and employment, reinforce vehicle dependence. In contrast, most European metropolitan areas, with higher densities and more centralised land-use patterns, have lower levels of car use. Stronger controls on land use employed in many European countries are seen as having preserved the compact form of metropolitan areas. These arguments imply significant relationships between land-use patterns and travel behaviour. Using travel diary data from the US and Great Britain, these relationships are compared across the two countries. It is found that differences in daily trips and miles travelled are explained by differences in both the urban form and household income. While the effect of income on daily travel is similar for the US and Great Britain, the effect of density is more pronounced in the US.

Employment Concentrations in Los Angeles, 1980–2000

Are contemporary metropolitan regions becoming more dispersed? There are theoretical arguments for both concentration and dispersal. The purpose of our research is to establish an empirical base that can help us to understand the evolution of metropolitan spatial structure. Using data for the Los Angeles region from 1980, 1990, and 2000, we identify employment centers and describe spatial trends in the pattern of employment inside and outside these centers. We find: (1) a remarkable degree of stability in the system of centers; (2) an increase in the average distance of jobs from the traditional core; (3) the emergence and growth of employment centers; (4) the rapid growth of dispersed employment in outer suburbs. These trends appear to defy simple models of urban evolution and call for a more nuanced portrayal of contemporary regions and the dynamics underlying spatial organization.

Low Income, Public Transit, and Mobility

A fundamental justification for transit subsidies in the United States is to provide a basic level of mobility to all persons, especially the transportation disadvantaged: those who are either unwilling or unable to drive or who do not have access to a car. Yet even among the disadvantaged, most travel is by private vehicle. This paper examines the role of transit in the daily travel patterns of low-income households. Public transit is used for only a small portion of travel, and those who use transit regularly have the lowest level of mobility among all population segments. Attitudinal data indicate dissatisfaction with public transit, suggesting that current trends are likely to continue. Retaining existing markets by improving service frequency and quality in high-demand markets, exploring more effective ways of providing transit in low-demand markets, and expanding transit to serve off-peak and off-direction commutes would make transit a more attractive option for everyone.

Travel, location and race/ethnicity

Abstract This paper examines the relationship between residential location and travel among ethnic and racial population segments using the 1995 US Nationwide Personal Transportation Survey (NPTS) data. Using measures of total daily travel, I explore the effects of metropolitan location and local neighborhood characteristics. I estimate models which test for both independent and interaction effects of race/ethnicity. I find that there are significant differences in travel characteristics across race/ethnic groups. There are independent effects associated with race/ethnicity. Individual characteristics such as sex, age and household income, have different effects on daily travel. Metropolitan location is not related to total daily travel. However, residential neighborhood characteristics are related and have different effects across race/ethnic groups. I conclude that our understanding of travel behavior is largely an understanding of the white majority population, which dominates analysis when race/ethnicity is not explicitly considered.

The Determinants of Growth of Employment Subcenters

This paper presents an empirical analysis of subcenter growth. We develop a series of hypotheses based on the theoretical concepts that have been proposed as explanations for the emergence and growth of subcenters. We then conduct tests of these hypotheses using 1970-80 data from the Los Angeles region. We find that subcenters containing fast-growing industries tended to grow rapidly, and so did those close to airports. There is weak evidence that large subcenters and those located near downtown Los Angeles grew more slowly in proportional terms, possibly indicating diseconomies of scale due to congestion.

Environmental sustainability in seaports: a framework for successful innovation

Environmental sustainability in the port industry is of growing concern for port authorities, policy makers, port users and local communities. Innovation can provide a solution to the main environmental issues, but often meets resistance. While certain types of technological or organisational innovation can be satisfactorily analysed using closed system theories, in the case of seaports and in particular in the area of environmental sustainability, more advanced conceptual frameworks have to be considered. These frameworks need to be able to account for the multiple stakeholder nature of the port industry and of the network and vertical interactions that environmental sustainability calls for. This article investigates successful innovations improving environmental sustainability of seaports. The proposed framework builds in part on research concepts developed in the InnoSuTra EU FP7 project. From a methodological perspective, this article develops a method for quantifying the degree of success of innovation with respect to a set of specific objectives. Several case studies are used to test the framework against real innovation examples, such as onshore power supply, or alternative fuels. In this article, we argue that only those innovations that fit dynamically port actors’ demands and the port institutional environment stand a chance to succeed.

Network Accessibility and Employment Centres

This research examines the impact of accessibility on the growth of employment centres in the Los Angeles region between 1990 and 2000. There is extensive empirical documentation of polycentricity—the presence of multiple concentrations of employment—in large metropolitan areas. However, there is limited understanding of the determinants of growth of employment centres. It has long been held that transport investments influence urban structure, particularly freeways and airports. Using data on 48 employment centres, the effects are tested of various measures of accessibility on centre employment growth: highway accessibility, network accessibility and two measures of labour force accessibility. Access to airports is also tested. It is found that, after controlling for centre size, density, industry mix, location within the region and spatial amenities, labour force accessibility and network accessibility are significantly related to centre growth. It is concluded that accessibility continues to play an important role in urban spatial structure.

Impact of high occupancy vehicle lanes on carpooling behavior

High occupancy vehicle lanes have become an integral part of regional transportation planning. Their purpose is to increase ridesharing by offering a travel time advantage to multiple occupant vehicles. This paper examines the extent to which an HOV facility increases ridesharing. Using data from the Route 55 HOV facility in Orange Country, California, changes in the carpooling rate on Route 55 are compared to that of a control group of freeway commuters. The analysis shows that the carpooling rate among peak period commuters, and particularly those who use the entire length of the facility, has increased. However, there has been no significant increase in ridesharing among the entire population of Route 55 commuters. Results suggest that barriers to increased ridesharing are formidable, that travel time savings must be large in order to attract new carpoolers, and that further increases in capooling will likely require development of extensive HOV lane systems.

Accessibility and Residential Land Values: Some Tests with New Measures

Accessibility is a fundamental concept in theories of metropolitan spatial structure. Urban economic models explain urban structure as a function of access to jobs; accessibility is capitalised into land values, which in turn explain the population distribution. Studies of residential land values show that many factors contribute to the value of a given location: the characteristics of the housing unit, its location with respect to social and environmental amenities, as well as access to jobs, services and other economic opportunities. Empirical studies typically use job access as a proxy for more generalised access to economic activities. However, jobs represent many different activities, from retail shopping to heavy manufacturing, and the value of access to these activities may be positive or negative. In this paper, accessibility measures based on industry sectors have been developed, allowing the separating out of possible different effects. Their impacts are tested on residential land values using data from the Los Angeles region. A multilevel modelling approach is used in order to control for neighbourhood-level attributes common to multiple properties. It is found that the various access measures have different and significant effects on land values, but attributes of the dwelling unit, together with access to the coast, explain most of the variation. The multilevel model is confirmed; there is significant correlation among properties within the same neighbourhood.