published journal article
working paper
The vast majority of the safety studies concerning added freeway lanes are based on pre-project versus post-project comparisons of accident rates for the project area only. There are two potential problems with such an approach: First, accurate traffic volume data are required for both the pre-project and post-project periods in order to provide exposure measures in the calculation of accident rates. Experience has shown that the accuracy of traffic volume data is often suspect, particularly in the period prior to reconstruction of a roadway section; repairs to induction-loop counting devices are often delayed to coincide with the construction involving the lane addition. Consequently, in many cases traffic counts in the pre-project period, and sometimes counts in both the pre- and post-project periods, are based on projections from actual counts taken years before. Because added capacity can induce latent demand for travel on the affected section of freeway, the pre-project and post-project periods can be substantially different than predicted by ordinary projection methods. Inaccuracies in the denominators of aggregate accident rate statistics can lead to false conclusions regarding project safety. Comparisons with “control” sections of roadway can be used in the absence of good exposure data. The second problem with aggregate comparisons of accident rates in the project section for pre-project versus post-project periods is that the additional capacity might affect accident risks in adjacent sections of roadway. If this occurs, it is potentially misleading to define the roadway only within the project area as the spatial unit of analysis in the accident rate comparisons. This precludes the ability to analyze possible spatial redistributions of accident locations due to the changes in the characteristics of traffic congestion from the pre-project to post-project periods. Moreover, the selection of the specific area of roadway for project location might be related to its accident history. The treated section of roadway might be a “blackspot” for a number of reasons, but the random nature of accident occurrence is a component in the historical process. It has been shown that a form of selectivity bias called “regression to the mean” (Hauer, 1980a, 1980b) can lead to overestimation of the reductions in accident rates resulting from safety-improvement projects. Such bias can also lead to overestimation of accident migration from treated (project) to non-treated (adjacent) roadway sections (Stein, 1984; McGuigan, 1985). Particularly with regard to added freeway lanes, there might be a migration of accidents from the project area and from upstream of the project area to bottlenecks downstream of the project area, due to the partial relief of congestion in one area and increased traffic flow to another area of congestion. Similarly, there might be a relief of congestion in areas upstream of the project area. Previous studies have recognized the need for “influence” areas (e.g., Urbanik and Bonilla, 1987), but it is difficult to assess the nature of any accident “migration” in terms of aggregate accident rate statistics. The present study attempts to characterize influences through a disaggregate spatial analysis of accident locations.
conference paper
published journal article
In spite of the popularity of e-shopping, only 16% of US adults have ordered groceries online, and 7 out of 10 of those who currently buy groceries online do so at most twice a month. Understanding the determinants of e-grocery shopping is important for grocers, supply chain managers, and urban planners. In this context, we first explore how deliveries from online shopping have been changing over time. From our analysis of the 2009 and 2017 National Household Travel Surveys, we found that online shopping has been embraced by increasingly diverse households, although income, education, and some racial/ethnic differences persist. Our analysis of the 2017 American Time Use Survey shows that Americans are 24 times more likely to shop for groceries in stores than online. Moreover, in-store grocery shoppers are more likely to be female and unemployed, but less likely to belong to younger generations, to have less than a college degree, or to be African American. The gender imbalance in grocery shopping is larger online than in stores, but e-grocery shoppers do not otherwise differ from the general population. Future travel and e-shopping surveys (especially for e-grocery) should combine time use and travel questions with retrospective questions about online purchases.
published journal article
The vehicle reidentification problem is the task of matching a vehicle detected at one location with the same vehicle detected at another location from a feasible set of candidate vehicles detected at the other location. This paper formulates and solves the vehicle reidentification problem as a lexicographic optimization problem. Lexicographic optimization is a preemptive multi-objective formulation, and this lexicographic optimization formulation combines lexicographic goal programming, classification, and Bayesian analysis techniques. The solution of the vehicle reidentification problem has the potential to yield reliable section measures such as travel times and densities, and enables the measurement of partial dynamic origin/destination demands. Implementation of this approach using conventional surveillance infrastructure permits the development of new algorithms for ATMIS (Advanced Transportation Management and Information Systems). Freeway inductive loop data from SR-24 in Lafayette, California, demonstrates that robust results can be obtained under different traffic flow conditions.
published journal article
working paper
Regulators concerned with traffic related emissions on large networks should consider allowing modelers to use mesoscopic traffic models (such as the MCDKW model) that can adequately represent congestion along with appropriate emissions models. This would simplify regulatory analyses, reduce errors, and cut costs.
working paper
In-laboratory experimentation with interactive microcomputer simulation is a useful tool for studying the dynamics of driver behavior in response to advanced traveler information systems. Limited real-world implementation of these information systems has made it difficult to observe and study how drivers seek, acquire, process, and respond to real-time information. This paper describes the design and preliminary testing of an interactive microcomputer-based animated simulator, developed at the University of California, Irvine, to model pre-trip and enroute driver travel choices in the presence of advanced traveler information systems. The advantages of this simulator are realized in its versatility to model driver decision processing while presenting a realistic representation of the travel choice domain. Results from a case study revealed that increased driver familiarity with travel conditions and network layout reduces driver reliance on information systems and influences drivers diversion behavior.
working paper |
Dec 1994
working paper |
Sep 1994
working paper |
Oct 1993
working paper |
Jan 1997
book/book chapter |
Oct 1998
published journal article
In the past 10 years the taxicab industry in the USA has begun entering into service contracts with public agencies. These are demand responsive transit (DRT) systems and consist of DRT for the general public and for the elderly and/or handicapped; additionally, there fixed-route transit services. The cost-effectiveness both for the public and the taxi companies, and the annual revenue to the latter is assessed. Other financial implications are considered.-J.W.Cooper
published journal article
This paper studies a mixed-service operation of shared-use autonomous mobility systems (SAMS) where customers can request rides either immediately or through reservations and use the vehicle for a point-to-point service or a time-slot-based rental service, respectively. Three autonomous-vehicle-to-user assignment strategies are presented: a first-come-first-served strategy and two optimization-based (bipartite matching) strategies. The mathematical formulations attempt to achieve a good trade-off between the wait times of reservation-based users and on-demand users, while minimizing overall empty fleet miles. A case study in Chicago is presented using taxi data, and the combined mixed-service fleet operation is compared with a case with two separate operations: one for an on-demand point-to-point service and one for a reservation-based time-slot rental service. Results show that a combined mixed-service operation can provide a more balanced service than the case with two separate operations with respect to the key performance measures of wait time and empty fleet miles.
