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Open Access Publications from the University of California

Recent Work

The UC Berkeley Center for Future Urban Transport was established in 2004 after the Volvo Research and Educational Foundations designated it as a Volvo Center of Excellence in a competition involving a large field of international candidates. It is housed at the Institute of Transportation Studies at the University of California, Berkeley, and its director is Carlos Daganzo, Professor of Civil and Environmental Engineering.

The Center's mission is to study the mutual interdependence of urban transportation policy and technology and use the understanding of that concept to devise sustainable transportation strategies for the world's cities.

It addresses this undertaking on three levels:

  • strategic, so that the research is guided by a city's vision of its own future;
  • tactical, where policies are tailored for specific environments; and
  • operational, where technologies are developed and the results fed back into tactical-level decisions.

The Center's research is divided into five research areas:

  • Mobility & Accessibility
  • Adapting to Urban Form
  • Telework Solutions
  • Congestion Mitigation
  • Wireless Infrastructure

Cover page of A congestion mechanism for uphill expressways, Part I: the shoulder lane "release valve"

A congestion mechanism for uphill expressways, Part I: the shoulder lane "release valve"

(2010)

A mechanism is unveiled by which congestion forms and persists near the base of an uphill expressway segment, causing significant reductions in output flow. The traffic condition in the expressway's shoulder lane is key to the mechanism. When shoulder-lane flow was low, drivers maneuvered around speed disturbances that periodically arose in the median lane. The shoulder lane accommodated high rates of vehicle migrations, thus acting as a "release valve" for the excess accumulation created by the speed disturbances. The release valve failed only when demand increased later in the rush. The resulting higher flows in the shoulder lane impeded drivers' attempts to maneuver around the median-lane speed disturbances that occurred thereafter. These attempts disrupted traffic and spread the excess accumulation laterally across all lanes. When this queue filled the approach to the hill, vehicles arrived to its base at low speeds. This impeded vehicle ascent; output flow dropped by about 10%; and this state of affairs persisted for the remainder of the rush.

The more conspicuous details of this mechanism were observed in loop detector data measured over many days at the site, and are consistent with observations previously made at other sites. The more subtle details became visible by examining thousands of vehicle trajectories extracted from a series of eleven roadside video cameras. Many of the subtleties are compatible with an existing theory of multi-lane traffic. All of this suggests that the present findings can be generalized to other uphill expressway segments. Practical implications are discussed.

Cover page of Unintended environmental impacts of nighttime freight logistics activities

Unintended environmental impacts of nighttime freight logistics activities

(2009)

In recent years, the reduction of freight vehicle trips during peak hours has been a common policy goal. To this end, policies have been implemented to shift logistics operations to nighttime hours. The purpose of such policies has generally been to mitigate congestion and environmental impacts. However, the atmospheric boundary layer is generally more stable during the night than the day. Consequently, shifting logistics operations to the night may increase 24‐hour average concentrations of diesel exhaust pollutants in many locations. This paper presents realistic scenarios for two California cities, which provide exhaust concentration and human intake estimates after temporal redistributions of daily logistics operations. Estimates are made for multiple redistribution patterns, including from 07:00‐19:00 to 19:00‐0:700, similar to daytime congestion charging polices and from 03:00‐18:00 to 18:00‐03:00, corresponding to the PierPASS program at the ports of Los Angeles and Long Beach. Results for these two redistribution scenarios indicate that 24‐hour average exhaust concentrations would increase at most locations in California, and daily human intake is likely to worsen or be unimproved at best. These results are shown to be worse for inland than coastal settings, due to differences in meteorology. Traffic congestion effects are accounted for, using a new graphical method, which depicts how off‐peak policies can be environmentally improving or damaging, depending on traffic speeds and meteorology. An investigation into the decreasing marginal environmental benefits of off‐policies is then provided, through the application of traffic flow theory. Finally, related environmental and human exposure concerns are considered to provide a comprehensive policy discussion of the environmental effects of shifting logistics operations from day to night.

Cover page of Multimodal Traffic at Isolated Signalized Intersections: New Management Strategies to Increase Capacity

Multimodal Traffic at Isolated Signalized Intersections: New Management Strategies to Increase Capacity

(2009)

New ideas are explored for managing multimodal traffic on isolated approaches to signalized intersections. Strategies are proposed that both: segregate distinct modes along the approach, and more effectively resolve the disruptive capacity-reducing conflicts that arise between through moving and turning traffic traveling in adjacent lanes. The proposed schemes produce capacities that consistently and significantly exceed those of conventional intersection treatments, and reduce travel delays for all modes. Observations at a real intersection support these claims.

Cover page of Managing Evacuation Routes

Managing Evacuation Routes

(2009)

This paper shows that evacuation routes, such as a building’s stairwell or an urban freeway, may discharge inefficiently if left unmanaged, and that setting priority rules can speed up egress. Therefore, a simple control strategy is proposed. The strategy is decentralized and adaptive, based on readily available real-time data. The strategy is shown to be optimal in two senses: (i) it finishes the evacuation in the least possible time, and (ii) it evacuates the maximum number of people at all times. In both cases, it favors the people most at risk. The results shed light on other traffic problems.

Cover page of Structure of Competitive Transit Networks

Structure of Competitive Transit Networks

(2009)

This paper describes the network shapes and operating characteristics that allow a transit system to deliver a level of service competitive with that of the automobile. To provide exhaustive results for service regions of different sizes and demographics, the paper idealizes these regions as squares, and their possible networks with a broad and realistic family that combines the grid and the hub-and-spoke concepts. The paper also shows how to use these results to generate master plans for transit systems of real cities.

The analysis reveals which network structure and technology (Bus, BRT or Metro) delivers the desired performance with the least cost. It is found that the more expensive the system’s infrastructure the more it should tilt toward the hub-and-spoke concept. Both, Bus and BRT systems outperform Metro, even for large dense cities. And BRT competes effectively with the automobile unless a city is big and its demand low. Agency costs are always small compared with user costs; and both decline with the demand density. In all cases, increasing the spatial concentration of stops beyond a critical level increases both, the user and agency costs. Too much spatial coverage is counterproductive.

Cover page of Unintended Impacts of Increased Truck Loads on Pavement Supply-Chain Emissions

Unintended Impacts of Increased Truck Loads on Pavement Supply-Chain Emissions

(2009)

In recent years, the reduction of freight truck trips has been a common policy goal. To this end, policies aimed at influencing load consolidation, load factors and increasing maximum truck weight limits have been suggested and implemented, resulting in higher gross vehicle weights. The purpose of such policies has generally been to mitigate congestion and environmental impacts. However, trucks cause most of the damage incurred by pavements. The supply chain associated with pavement maintenance and construction releases significant air emissions, raising the question of whether increased vehicle weights may cause unintended environmental consequences. This paper presents scenarios with estimated emissions resulting from load consolidation and changes in load factors. These scenarios reveal several points having to do with the tradeoff between tailpipe versus pavement supply‐chain emissions. In some cases, unintended emissions from the pavement supply‐chain are found to be significant. Emissions associated with pavement construction are also found to increase as a result of pavement design specifications that account for heavier trucks.

Cover page of Structure of Competitive Transit Networks

Structure of Competitive Transit Networks

(2009)

This paper describes the network shapes and operating characteristics that allow a transit system to deliver a level of service competitive with that of the automobile. To provide exhaustive results for service regions of different sizes and demographics, the paper idealizes these regions as squares, and their possible networks with a broad and realistic family that combines the grid and the hub-and-spoke concepts. The paper also shows how to use these results to generate master plans for transit systems of real cities. The analysis reveals which network structure and technology (Bus, BRT or Metro) delivers the desired performance with the least cost. It is found that the more expensive the system’s infrastructure the more it should tilt toward the hub-and-spoke concept. Both, Bus and BRT systems outperform Metro, even for large dense cities. And BRT competes effectively with the automobile unless a city is big and its demand low. Agency costs are always small compared with user costs; and both decline with the demand density. In all cases, increasing the spatial concentration of stops beyond a critical level increases both, the user and agency costs. Too much spatial coverage is counterproductive.

Cover page of Multimodal Transport Modeling for Nairobi, Kenya: Insights and Recommendations with an Evidence-Based Model

Multimodal Transport Modeling for Nairobi, Kenya: Insights and Recommendations with an Evidence-Based Model

(2009)

Traffic congestion is a growing problem in Nairobi, Kenya, resulting from rapidly increasing population and the crowding of motorized traffic onto a limited street network. This report includes analysis of the traffic conditions in Nairobi, the expected effects of further growth in demand, and a set of recommendations for how to improve the performance of the street network. Data describing motorized vehicle traffic was used to build a simulation model of Nairobi’s street network considering cars and matatus. This model was used to analyze traffic conditions at the city-scale under existing conditions and future growth scenarios. The results provide insights for improving the network performance and support recommendations for Nairobi. City-scale analysis of the street network was conducted with the use of the macroscopic fundamental diagram (MFD) which relates the number of vehicles circulating on the street network to the rate at which trips reach their destinations. The results of simulations with different demand patterns show that there is a consistent MFD relating vehicle accumulation to network flow in Nairobi’s central business district (CBD). Therefore, detailed knowledge of demand is not necessary to understand how the network performs, because the MFD depends on the properties of the street network itself. Monitoring and controlling the number of vehicles in the network is sufficient to maintain traffic flow on the city’s streets. As traffic demand grows in the future, the streets will quickly become more congested, so measures should be taken to improve the system. The first recommendations seek to control the accumulation of vehicles in the network so that traffic flow is maximized according to the MFD. One method is to meter the rate at which vehicles can enter the CBD in order to control accumulation so that everyone can reach their destinations sooner. Metering can be effective in the morning when more vehicles are entering the CBD from outside, but during the evening there are many internally generated trips which will tend to jam the network anyway. Policies that reduce the peak travel demand by shifting trips to public transport or spreading the demand across more time can reduce traffic congestion in the evening. A second set of recommendations expand the shape of the MFD itself by increasing the capacity of the streets in the network which is largely dependent on how intersections operate. Traffic circles (roundabouts) are common in Nairobi, but signalized intersections can have greater capacity. Converting intersections will also reduce the congestion effects when queues spill back into upstream intersections. Capacity can be further increased by adding redundancy to the network. An analysis of dedicating lanes to buses and matatus on radial arterials shows that queues in the remaining lanes will grow longer. In the morning, these queues grow away from the center, so matatus experience reduced travel times, but in the evening, the queues back up into CBD increasing delays for everyone. The simulation study provides an illustration representing Nairobi approximately, so results are relevant and qualitatively useful. Further data could be collected to estimate the real MFD for Nairobi and provide more accurate quantitative values. Although Nairobi’s streets are congested and bound to get worse, the network performance can be improved by making strategic investments in the transport network.

Cover page of Evaluation of Traffic Data Obtained via GPS-Enabled Mobile Phones: the Mobile Century Field Experiment

Evaluation of Traffic Data Obtained via GPS-Enabled Mobile Phones: the Mobile Century Field Experiment

(2009)

The growing need of the driving public for accurate traffic information has spurred the deployment of large scale dedicated monitoring infrastructure systems, which mainly consist in the use of inductive loop detectors and video cameras. On-board electronic devices have been proposed as an alternative traffic sensing infrastructure, as they usually provide a cost-effective way to collect traffic data, leveraging existing communication infrastructure such as the cellular phone network. A traffic monitoring system based on GPS-enabled smartphones exploits the extensive coverage provided by the cellular network, the high accuracy in position and velocity measurements provided by GPS devices, and the existing infrastructure of the communication network. This article presents a field experiment nicknamed Mobile Century, which was conceived as a proof of concept of such a system. Mobile Century included 100 vehicles carrying a GPS-enabled Nokia N95 phone driving loops on a 10-mile stretch of I-880 near Union City, California, for 8 hours. Data were collected using virtual trip lines, which are geographical markers stored in the handset that probabilistically trigger position and speed updates when the handset crosses them. The proposed prototype system provided sufficient data for traffic monitoring purposes while managing the privacy of participants. The data obtained in the experiment were processed in real-time and successfully broadcast on the internet, demonstrating the feasibility of the proposed system for real-time traffic monitoring. Results suggest that a 2-3% penetration of cell phones in the driver population is enough to provide accurate measurements of the velocity of the traffic flow.

Cover page of Bus Rapid Transit Impacts on Land Uses and Land Values in Seoul, Korea

Bus Rapid Transit Impacts on Land Uses and Land Values in Seoul, Korea

(2009)

More and more cities are turning to Bus Rapid Transit (BRT) as a way of cost-effectively expanding public transit services to help relieve traffic congestion, reduce carbon emissions, and increase mobility options for the poor. Because of the inherent flexibility advantages of rubber-tire buses – e.g., unlike rail systems, the same vehicle that functions as a line-haul carrier can also morph into a neighborhood feeder -- BRT is especially suited for many lower density and non- CBD settings.

Some of the most advanced and widely heralded BRT services today are found in Latin America, such as Curitiba and Sao Paulo, Brazil, Bogotá and Cali, Columbia, Santiago, Chile, and Lima, Peru. The success of BRT in these cities stems, to a large degree, from the presence of dedicated lanes, which offer significant speed advantages relative to more traditional mixed-traffic services. One of the few cities outside of Latin America that has joined the ranks of world-class BRT serviceproviders is Seoul, Korea. As in cities like Curitiba and Bogotá, Seoul operates dedicated median-lane BRT services which are supplemented by one of the most extensive networks of curbside BRT lanes anywhere. Seoul began implementing curbside bus lanes in 1986 however because of conflicts with traffic entering the main traffic stream these lanes failed to provide significant speed advantages. It was only after the addition of exclusive median lanes in 2004 that buses began to offer significant travel-time savings and win over former motorists.

All else being equal, significant gains in bus speeds should be followed by significant land-use changes, like densification and property value increases, especially in congested mega-cities like Seoul. Land markets can be expected to place a high premium on parcels close to transit corridors that enjoy significant travel-time savings since, after all, such settings have scarcity value – i.e., there is a finite, limited supply of settings with superior transit offerings. This paper probes this hypothesis by studying land-use changes and property-value increases induced by Seoul’s introduction of exclusive, median-lane BRT services. First, the empirical literature on bus transit and land-use impacts is reviewed. This is followed by background discussions on Seoul’s transportation conditions and BRT system. Next, we describe our research methodology and supporting data sources. We then present multilevel models that gauge the influences of upgrading BRT services on land-use changes and land values. The paper concludes by reflecting on the policy implications of the key research findings.