ITS Berkeley

A Reliability-based Optimization Scheme for Maintenance Management in Large-scale Bridge Networks

Hu, Xiaofei
Daganzo, Carlos F.
Madanat, Samer
2015

Incorporating network configurations in bridge management problems is computationally difficult. Because of the interdependencies among bridges in a network, they have to be analyzed together. Simulation-based numerical optimization techniques adopted in past research are limited to networks of moderate sizes. In this paper, a simple framework is developed to determine optimal maintenance plans for large networks with many bridges. The objective is to minimize disruption, specifically, the extra travel distance caused by potential bridge failures over a planning horizon and under a budget...

Allocating City Space to Multiple Transportation Modes: A New Modeling Approach Consistent with the Physics of Transport

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2008

A macroscopic modeling approach is proposed for allocating a city’s road space among competing transport modes. In this approach, a city or neighborhood street network is viewed as a reservoir with aggregated traffic. Taking the number of vehicles (accumulation) in a reservoir as input, we show how one can reliably predict system performance in terms of person and vehicle hours spent in the system and person and vehicle kilometers traveled. The approach is used here to unveil two important results: first, that restricting access to a city’s congested areas can improve mobility for all...

How to Improve Bus Service

Daganzo, Carlos F.
2008

Bus schedules cannot be easily maintained on busy lines with short headways: Experience shows that buses offering this type of service usually arrive irregularly at their stops, often in bunches. Although transit agencies build slack into their schedules to alleviate this problem, their attempts often fail because practical amounts of slack cannot prevent large localized disruptions from spreading system-wide. This paper describes a more resilient control scheme that overcomes this problem. The method also produces even headways with less slack than the conventional approach. Thus, buses...

An Analytical Approximation for the Macroscopic Fundamental Diagram of Urban Traffic

Daganzo, Carlos F.
Geroliminis, Nikolas
2008

This paper shows that a macroscopic fundamental diagram (MFD) relating average flow and average density must exist on any street with blocks of diverse widths and lengths, but no turns, even if all or some of the intersections are controlled by arbitrarily timed traffic signals. The timing patterns are assumed to be fixed in time. Exact analytical expressions in terms of a shortest path recipe are given, both, for the street’s capacity and its MFD. Approximate formulas that require little data are also given. For networks, the paper derives an upper bound for average flow conditional on...

Existence of Urban-Scale Macroscopic Fundamental Diagrams: Some Experimental Findings

Geroliminis, Nikolaos
Daganzo, Carlos F.
2008

A field experiment in Yokohama (Japan) reveals that a macroscopic fundamental diagram (MFD) linking space-mean flow, density and speed exists on a large urban area. The experiment used a combination of fixed detectors and floating vehicle probes as sensors. It was observed that when the somewhat chaotic scatter-plots of speed vs. density from individual fixed detectors were aggregated the scatter nearly disappeared and points grouped neatly along a smoothly declining curve. This evidence suggests, but does not prove, that an MFD exists for the complete network because the fixed detectors...

Effects of High Occupancy Vehicle Lanes on Freeway Congestion

Daganzo, Carlos F.
Cassidy, Michael J.
2008

Previous research on the effect of HOV (high occupancy vehicle) lanes on bottleneck flows is extended here to entire freeways using both theory and empirical evidence. The paper shows that if the flows of both high- and low-occupancy vehicles remain invariant before and after a freeway lane is converted to HOV use, then the freeway’s overall traffic density upstream of its bottlenecks is reduced – albeit less than expected – if the HOV lane is underutilized. As a result, HOV lanes can extend queues over longer distances. These expansions can be problematic if the queues’ expanded portions...

Spatiotemporal Effects of Segregating Different Vehicle Classes on Separate Lanes

Cassidy, Michael J.
Daganzo, Carlos F.
Jang, Kitae
Chung, Koohong
Lam, William H. K.
Wong, S.C.
Lo, Hong K.
2009

The paper explores some of the impacts of setting aside road lanes for the exclusive use of select vehicle classes. We examine first the case of lanes that are reserved for carpools, and then extend the analysis to bus-only lanes. In doing so, the paper makes three contributions. The first is methodological: it illustrates the importance of analyzing freeway data in full spatiotemporal detail. The second is physical: data reveal that carpool lanes are not as damaging as previously reported. In fact, these lanes are found to smooth traffic in adjacent lanes so much (by diminishing...

Smoothing Effect on Freeway Bottlenecks: Experimental Verification and Theoretical Implications

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2009

Real data show that reserving a lane for carpools on congested freeways induces a smoothing effect that is characterized by significantly higher bottleneck discharge flows (capacities) in adjacent lanes. The effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. The effect is reproducible across days and freeway sites: it was observed, without exception, in all cases tested; and queueing analysis shows that the effect greatly reduces the times spent traveling on a freeway. The effect is so significant, in fact, that even a severely...

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

Gonzales, Eric J.
Chavis, Celeste
Li, Yuwei
Daganzo, Carlos F.
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...

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

Xuan, Yiguang
Gayah, Vikash
Daganzo, Carlos
Cassidy, Michael
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.