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Open Access Publications from the University of California

California PATH is a unique research organization. It focuses on solving California's and the nation's transportation problems by conducting relevant and high-quality research that advances the state of the art. The research is performed by a statewide group of faculty, graduate students, and research staff of diverse backgrounds and expertise working closely together. At the same time, PATH produces the next generation of leaders in academia and the transportation profession. PATH's ongoing research directly addresses the mobility, reliability, and safety goals of our Caltrans (California Department of Transportation) partners and will place major emphasis on field testing of the most promising strategies for traffic control, traveler information, intersection safety, transit, and other mobility options.

Alexander Skabardonis, Adjunct Professor of Civil and Environmental Engineering and Research Engineer at the Institute of Transportation Studies, is PATH's director.

Cover page of A Multi-channel VANET Providing Concurrent Safety and Commercial Services

A Multi-channel VANET Providing Concurrent Safety and Commercial Services


One of the key goals of a vehicular ad-hoc network (VANET) is providing sufficient quality of service (QoS) for real-time safety applications while concurrently supporting commercial services. This paper proposes a multi-channel wireless communication architecture and protocol for the scenario where commercial services are provided by roadside infrastructure. This solution extends the IEEE 802.11 wireless LAN protocol to schedule periodic safety messages in a "safety channel". It explicitly supports concurrent non-time-critical communications in separate, non-safety "service channels". Further, it is shown that this arrangement maximizes service channel access time while maintaining the requisite QoS for safety applications. This paper concludes with simulations that confirm the attractive properties of this architecture and protocol.

Cover page of Berkeley Highway Lab Videl Data Collection System

Berkeley Highway Lab Videl Data Collection System


The goal of this project is to replace the existing analog video collection system on the roof of Pacific Park Plaza (PPP) with a digital one. This video collection system is part of the Berkeley Highway Laboratory (BHL) testbed. It records video of traffic on a continuous one-kilometer section of Interstate 80 (I-80) near Emeryville, CA. This section of I-80 features on-ramps, off-ramps, and weaving zones. The video of interactions between vehicles can be fed to a machine-vision system, which generates vehicle trajectories to be used in a variety of traffic studies. The video itself can also be used for both human and machine-vision based verification of loop data.

Cover page of Traffic Measurement and Vehicle Classification with a Single Magnetic Sensor

Traffic Measurement and Vehicle Classification with a Single Magnetic Sensor


Wireless magnetic sensor networks offer a very attractive, low-cost alternative to inductive loops for traffic measurement in freeways and at intersections. In addition to vehicle count, occupancy and speed, the sensors yield traffic information (such as vehicle classification) that cannot be obtained from loop data. Because such networks can be deployed in a very short time, they can also be used (and reused) for temporary traffic measurement. This paper reports the detection capabilities of magnetic sensors, based on two field experiments. The first experiment collected a two-hour trace of measurements on Hearst Avenue in Berkeley. The vehicle detection rate is better than 99 percent (100 percent for vehicles other than motorcycles); and estimates of vehicle length and speed appear to be better than 90 percent. Moreover, the measurements also give inter-vehicle spacing or headways, which reveal such interesting phenomena as platoon formation downstream of a traffic signal. Results of the second experiment are preliminary. Sensor data from 37 passing vehicles at the same site are processed and classified into 6 types. Sixty percent of the vehicles are classified correctly, when length is not used as a feature. The classification algorithm can be implemented in real time by the sensor node itself, in contrast to other methods based on high scan-rate inductive loop signals, which require extensive offline computation. We believe that when length is used as a feature, 80-90 percent of vehicles will be correctly classified.

Cover page of PEDAMACS: Power Efficient and Delay Aware Medium Access Protocol for Sensor Networks

PEDAMACS: Power Efficient and Delay Aware Medium Access Protocol for Sensor Networks


We consider a class of sensor networks with two special characteristics. First, the nodes periodically generate data for transfer to a distinguished node called the access point. Second, the nodes are (transmit) power and energy limited, but the access point, which communicates with the 'outside world', is not so limited. Such networks might be used for instance when a geographically distributed physical process, such as traffic on a freeway or at an urban street intersection, is periodically sensed for purposes of process control. We propose a medium access control scheme, called PEDAMACS, for this special class of networks. PEDAMACS uses the high-powered access point to synchronize the nodes and to schedule their transmissions and receptions in a TDMA manner. The protocol first enables the access point to gather topology (connectivity) information. A scheduling algorithm then determines when each node should transmit its data, and the access point announces the transmission schedule to the other nodes. The scheduling algorithm ideally should minimize the delay-the time needed for data from all nodes to reach the access point. However, this optimization problem is NP-complete. PEDAMACS instead uses a polynomial-time scheduling algorithm which guarantees a delay proportional to the number of nodes in the sensor network. Because PEDAMACS schedules node transmissions, its performance is much better than that of protocols designed for more general contention (or random access) networks in terms of power consumption, delay, fairness, and congestion control. The comparison is based on simulations in TOSSIM, a simulation environment for TinyOS, the operating system for the Berkeley sensor nodes. For the traffic application we consider, the PEDAMACS network provides a lifetime of several years compared to several months and days based on random access schemes with and without sleep cycles respectively, making sensor network technology economically viable.

Cover page of An Assessment of Bus Rapid Transit Opportunities in the San Francisco Bay Area

An Assessment of Bus Rapid Transit Opportunities in the San Francisco Bay Area


This report documents a continuing assessment of bus rapid transit opportunities in the San Francisco Bay Area. In this study we are focusing on bus transit routes that partially travel on California state routes, whether arterial roadways or freeways. A primary component of this project is to consider the inter-connectivity and regional aspects of bus rapid transit systems deployment in the San Francisco Bay Area region. Considering state routes will help identify more regional opportunities for innovative types of partnerships to help address unmet public transit service needs across jurisdictional boundary lines. We initially identified nearly 200 bus transit routes in the Bay Area that travel on state routes. Next we embarked on a multi-step process to reduce the field of bus routes to a select few with a high likelihood of being upgraded to bus rapid transit systems. We looked at the length of the bus transit routes that travel on state routes, service characteristics related to schedule and route structures based on passenger demand level, external factors, bus routes that function essentially as one service, and level of passenger demand. We selected the following five bus routes for further consideration, the first four of which are already under investigation to be upgraded to bus rapid transit. AC Transit Routes 72-72M-72R on SR 123 AC Transit Routes 82-82L along Telegraph Avenue/International Boulevard/14 th Street corridor SamTrans Routes 390/391 on SR 82 (El Camino Real) Santa Clara VTA Route 22 on SR 82 (El Camino Real) San Francisco Muni? route 9X in San Bruno

Cover page of Demand-Responsive Transit Shuttles: Who Will Use Them?

Demand-Responsive Transit Shuttles: Who Will Use Them?


Large urban areas often have rail systems that rely on feeder buses to expand their service area. This paper explores the possibility of expanding access to existing rail transit systems through demand-responsive shuttles. The study analyzes the effect of several factors on an individual's willingness to use a door-to-station shuttle service. Using survey data collected in a case study of one urban and one suburban neighborhood (N=800) served by the San Francisco Bay Area Rapid Transit, this paper uses descriptive statistics and ordered logit regression to investigate the influence of several factors on peoples's willingness to use the shuttles. The results indicate that 21% of the respondents were strongly inclined to at least trying the service and paying for it. Residents of the urban neighborhood and those who lived more than half a mile from the nearest transit station were more willing to use the shuttle. Interestingly, 20% of single-occupant automobile users in both the urban and suburban communities were highly willing to use the shuttle, if only on a trial basis. Furthermore, those who park-and-ride in the suburban neighborhood and those who carpool or ride transit in the urban neighborhood were most likely to try the proposed shuttle service.

Cover page of Traveler Response to New Dynamic Information Sources: Analyzing Corridor and Area-Wide Behavioral Surveys

Traveler Response to New Dynamic Information Sources: Analyzing Corridor and Area-Wide Behavioral Surveys


Intelligent Transportation Systems present a well-known innovation opportunity to address urban congestion and allow greater access to transportation networks. New sources of travel information are emerging rapidly and they are likely to significantly impact traveler decisions and transportation network performance. To assess the value and impact of these new sources, this paper develops a comprehensive conceptual model based on information processing and traveler response. Specifically, the model accounts for the effect of information source, content and quality on information access and travel behavior. The paper presents empirical evidence from several behavioral surveys conducted in the San Francisco Bay Area between 1995-1999.The surveys used innovative methods to study the response of the whole population, response of people more inclined to use information technology (early adopters), and traveler decision-making in high-benefit incident situations. The conceptual model helps us integrate and interpret empirical findings from the surveys. We discuss the issues of access to new and conventional technologies and services, their current market penetration levels, switching behavior regarding new information sources/information service providers, desired information content and willingness to pay for dynamic information. The opportunities and limitations of new technologies and the implications for future technology implementations are discussed.

Cover page of Vehicle Modeling and Verification of CNG-Powered Transit Buses

Vehicle Modeling and Verification of CNG-Powered Transit Buses


This report will present the results of the initial study to develop an accurate working model of the 40 foot New Flyer Bus powered by the Cummins C8.3+ 280G CNG engine (Figure 1.1). The main focus of the study is the modeling of the vehicle dynamics using step input acceleration data. Other parts of the research include gear shifting and torque production from the CNG engine, all of which are required to produce a completely simulationcapable bus model.