published journal article
research report
In California, there has been a growing concern about housing unaffordability and its negative consequences, but it has remained unclear how transportation is related to this issue. This report synthesizes the literature on the causes and consequences of local growth control which has been viewed as one of the most significant barriers to expanding housing supply and thus managing travel demand more effectively. Emphasis is on what insights can be gained from the literature and what further research is needed to better understand how transportation influences and is influenced by growth control actions.
policy brief |
Nov 2020
published journal article
published journal article
conference paper
In spite of their significance in freight modeling, freeway design and operation, varying truck flow patterns by season and time-of-day cannot be captured by current truck data sources such as surveys or point detectors. In this paper, a truck tracking algorithm was developed to estimate path flows of trucks by a linear data fusion method utilizing weigh-in-motion and inductive loop point detectors. The authors utilized a Selective Weighted Bayesian Model (SWBM) that tracks individual vehicles between two detector locations using truck physical attributes and waveform signatures. Selected truck features were identified and weighted via Bayesian modeling to improve vehicle matching performance. Data for model development were collected from two WIM sites in California, separated by 27 miles. The algorithm showed a high matching accuracy for the truck population tracking across longer distance. In a test data set, the model was able to successfully match 76 percent of trucks that traversed the corridor. Although only 21 percent of trucks observed at the downstream site traversed the corridor, only 18 percent of the matches predicted by the model were false matches. In a follow-up case study, the algorithm was implemented over a longer 65-mile distance of freeway section and showed that the proposed algorithm was capable of providing insights into truck travel patterns and industrial affiliation to yield a comprehensive truck activity data source.
working paper
Starting in the mid-1960’s, federal policy encouraged the public takeover and subsidy of what had been a privately owned, self-supporting transit industry. The combination of public ownership and subsidy was able to halt the long-term decline in ridership, but it also led to the growth of an enormous financial deficit that has become increasingly difficult to bear. This paper uses disaggregate data for 62 transit properties to measure the change in productivity (output per dollar of input) over the period 1950–1985. It also shows the relationship between productivity and the size of the transit property – the large transit properties showed the greatest declines in productivity. The evidence shows substantial diseconomies of scale too. The magnitude of the productivity decline is surprising: indeed, if transit productivity had merely remained constant since 1964, the year the federal subsidy program began, total operating expenses would be more than forty percent lower. To put that figure in perspective, this is enough cost reduction to erase most of the current operating deficit — without raising fares.
working paper |
Nov 1991
working paper |
Jun 1991
working paper |
Nov 1988
working paper |
Sep 1991
working paper |
Oct 1989
working paper
The recent fiscal problems of public transit in many large metropolitan areas have stimulated interest in alternative service delivery systems for public transportation. One strategy. that of contracting with private providers for public transportation services. has received particular attention. Private sector contracting is viewed as attractive due to its cost and subsidy savings potential–savings of 25 to 50 percent of public agency transit operator costs have been cited.(1.2.3) The reality. however. is that relatively little transit service contracting currently takes place and that substantial political, organizational, and legal obstacles confront plans to increase the use of this strategy. In addition, little detailed information is available on the extent of service contracting. its economic benefits. and the institutional factors which affect its feasibility. The purpose of this paper is to contribute to remedying this information deficiency by providing a review of selected experiences and issues of transit service contracting. The paper focuses on five major topics. (1) How widespread is transit service contracting. who practices it. and what services are involved? (2) Why do public agencies engage in private sector contracting, and what are typical situations in which they do so? (3) What is the magnitude of the estimated cost and subsidy savings which have been realized from contracting? (4) What are the major obstacles to service contracting and when are they able to be overcome? (5) What issues involving service contracting require additional research?
Phd Dissertation
Accidents are the largest source of external costs related to transportation in the United States with annual costs estimated to exceed $200 billion per year. Incidents also create traffic backups and delays that can result in secondary incidents (i.e., collisions that occur as a result of other incidents). Although incident management has received a lot of attention from academics and practitioners alike, secondary incidents have so far been somewhat neglected. The main purpose of this dissertation is to investigate empirically whether the implementation of changeable message signs (CMS), which are one Intelligent Transportation System tool, can reduce secondary collisions. After reviewing previously published methods for estimating secondary accidents, I implement a Binary Speed Contour Map approach to detect secondary incidents using PeMS data. I also estimate the extra time lost to congestion because of incidents. My study area is a portion of Interstate 5 that stretches 55 miles from the Mexico-US border to Northern San Diego County, CA. This freeway portion has an average annualized daily traffic volume of 230,000 vehicles. My unique dataset includes incident data for 2008 combined with detailed weather data, elements of freeway geometry, and information about CMS usage. I identify a total of 9,003 incidents in my study area in 2008. Using the BSCM approach, I find that 3.7 percent of collisions were secondary incidents. Moreover, my statistical model shows that incidents occurring during evening peak hours on Fridays or during midday on weekends are more likely to result in secondary crashes as do incidents with injuries or fatalities, incidents that involve more vehicles or trucks, or incidents that take place when the pavement is wet. Conversely, secondary crashes are less likely to occur in areas with a complex geometry (perhaps because drivers are more cautious there) or for incidents taking place on the side of the freeway. More importantly, changeable message signs (CMS) decrease the occurrence of secondary crashes. The maximum effectiveness of a CMS is approximately 11.75 miles for a range of 23.6 miles. Finally, annual incident-related congestion is approximately 1.9 hours per freeway vehicle, which represents five percent of the 37 hours of annual traffic delay experienced by the average San Diego motorist.
working paper
This paper studies the effects of tolling road use on a parallel network when different governments have tolling authority on the different links of the network. The paper analyses the tax competition between countries that each maximise the surplus of local users plus tax revenues. Three types of tolling systems are considered: (i) toll discrimination between local and transit traffic, (ii) uniform tolls on local and transit traffic, (iii) only local tolls can be imposed. The paper characterises the optimal toll levels chosen in a Nash equilibrium for the three tolling systems. The numerical illustration shows that introducing transit taxes generates large welfare effects and that toll systems that only apply to local users only generate a low welfare gain. Nash equilibrium toll discrimination between local and transit traffic generates slightly higher welfare than the solution where both tolls have to be uniform.
conference paper
DNN-based Adaptive Cruise Control (ACC) systems are very convenient but also safety critical. Although prior work has explored physical adversarial attacks on DNN models, those attacks are mostly static and their effects on a real-world ACC system are not clear. In this work, we propose the first end-to-end attack on ACC systems, and we test the safety indication on the state-of-the-art ACC products. The experimental results show that our approach can make the vehicle driving with ACC accelerate unsafely and cause a rear-end collision.