published journal article
published journal article
conference paper
conference paper
Taxicabs are certainly the most popular type of on-demand transportation service in urban areas because taxi dispatching systems offer more and better services in terms of shorter wait times and travel convenience. However, a shortage of taxicabs has always been critical in many urban contexts especially during peak hours and taxis have great potential to maximize their efficiency by employing shared-ride concept. There are recent successes in real-time ridesharing projects that are expected to bring substantial benefits on energy consumption and operation efficiency, and thus it is essential to develop advanced vehicle dispatch algorithms to maximize occupancy and minimize travel times in real-time. This paper investigates how taxi services can be improved by proposing shared-taxi algorithms and what type of objective functions and constraints could be employed to prevent excessive passenger detours. Hybrid Simulated Annealing (HSA) is applied to dynamically assign passenger requests efficiently and a series of simulations are conducted with two different taxi operation strategies. The simulation results reveal that allowing ride-sharing for taxicabs increases productivity over the various demand levels and HSA can be considered as a suitable solution to maximize the system efficiency of real-time ride sharing.
research report
published journal article |
Jan 1988
research report
The San Pedro Bay Ports (SPBP) complex of Los Angeles and Long Beach is the largest container port in the U.S., and a very important contributor to both California’s and the nation’s economies. Although the benefits of the SPBP activities are enjoyed by the whole country, the burden of the congestion and air pollution it generates falls mostly on the shoulders of people who live and work in the transportation corridor serving the SPBP. This corridor includes two busy freeways, the I-710 and the I-110, and a busy rail link, the Alameda corridor. The objective of this paper is to explore an integrated approach for evaluating the environmental and health impacts of freight operations between the SPBP complex and downtown Los Angeles, some 22 miles north. Our integrated approach combines a number of models, including a microscopic traffic simulation model and an emissions model to better estimate the impacts of congestion on air pollution, emission estimates from line-haul and switching train activities, a spatial dispersion model, and a health impact model. We analyze emissions for year 2005, which serves as a baseline in various air pollution inventories of the SPBP complex. Our results show that emissions concentrations are strongly affected by meteorological conditions and seasonal variations (winter is worse than summer); moreover, we found that health impacts from NOx and PM exposure exceed 200 million dollars, which justifies a number of regional initiatives to improve air quality. Our analysis is a starting point for analyzing the economic efficiency of these initiatives, which include modal shift (from trucks to trains) and the Clean Trucks Program.
policy brief |
Jan 2010
conference paper
conference paper
working paper
This research is concerned with the statistical analysis of accident counts at non-signalized intersections. The objective is to develop a method for determining general (non-linear) relationships between approach volumes and accident counts. The method must accommodate the testing of whether intersections of differing physical designs have higher or lower rates of accidents than predicted by traffic levels. It is assumed that only aggregate data are available: (1) counts of total accidents by type (e.g., injury versus property damage) without details concerning the locational position(s) of the vehicle(s) involved; and (2) aggregate traffic intensity on each intersection entry without details concerning turning volumes. The method involves the application of non-linear multivariate methods to variables treated as ordinal scales. A case study application involving four-leg and three-leg (“T”) non-signalized major arterial intersections in the Netherlands is described. The effect of bicycle traffic on accident rates is included in the case study analysis. The results indicate that there are three groups of each of the two types of intersections based on traffic flow patterns. For each group, a different functional form was found to relate accident rates and specific variables measuring traffic volumes. There were no significant differences among the physical design categories of the intersections in each group that were not accounted for by differences in traffic intensities.
published journal article
In the United States, particularly in high-cost urban areas, local resistance to multifamily housing development has been widely noted. In many metropolitan areas, legal authority over land-use regulation is assigned to jurisdictions that often are very small, and some scholars argue that this small-scale local control institutionalizes neighborhood-level opposition to new construction. Using census tracts as units of analysis, we assess the relationship between the population size of the city, county, or township that regulates a tract’s land use and the change in multifamily units between two recent waves of the American Community Survey (2008–2012 and 2014–2018). Results of regression analysis indicate that larger jurisdictional population size is indeed associated with increased multifamily construction. However, the relationship applies only for jurisdictions with populations exceeding 100,000 and decays at jurisdictional populations of more than 1 million. This nonlinearity may reflect quasi-monopolistic land-use control in the largest jurisdictions.