Traffic Operations and Management

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.

A Headway-based Approach to Eliminate Bus Bunching: Systematic Analysis and Comparisons

Daganzo, Carlos F.
2009

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 – if necessary holding buses at control points to stay on schedule – their attempts often fail because practical amounts of slack cannot prevent large localized disruptions from spreading system-wide. This paper systematically analyzes an adaptive control scheme to mitigate this problem. The proposed scheme...

The Smoothing Effect of Carpool Lanes on Freeway Bottlenecks

Cassidy, Michael J.
Jang, Kitae
Daganzo, Carlos F.
2010

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 is reproducible across days and freeway sites: it was observed, without exception, in all cases tested. Predicted by an earlier theory, the effect arises because disruptive vehicle lane changing diminishes in the presence of a carpool lane. We therefore conjecture that smoothing can also be induced by other means that would reduce lane changing. The benefits can be large....

Managing Evacuation Routes

So, Stella K.
Daganzo, Carlos F.
2010

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 evacuates the maximum number of people at all times, and (ii) it finishes the evacuation in the least possible time. In both cases, it favors the people most at risk. The results shed light on other traffic...

On the Stability of Freeway Traffic

Daganzo, Carlos F.
2010

Traffic flow theory is used to analyze the spatio-temporal distribution of flow and density on closed loop homogeneous freeways with many ramps, which produce inflows and allow outflows. It is shown that if the on-ramp demand is space-independent then this distribution tends toward uniformity in space if the freeway is either: (i) uncongested; or (ii) congested with queues on its on-ramps and enough inflow to cause the average freeway density to increase with time. In all other cases, including any recovery phase of a rush hour where the freeway's average density declines, the distribution...

Public Transportation Systems: Mini-Projects and Homework Exercises

Gonzales, Eric J.
Pilachowski, Josh
Gayah, Vikash V.
Cassidy, Michael
Daganzo, Carlos F.
2010

The Course Notes for a graduate-level course in Public Transportation include seven homework exercises and three mini-projects. Homework topics include optimization, point-to-point travel, congestion relief, designing a feeder bus system, demand-responsive transit, and bus pairings. The mini-projects involve bus rapid transit, designing a transit network, and bus and driver assignment.

On the Allocation of City Space to Multiple Transport Modes

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2010

This paper analyzes urban multimodal transportation systems in an aggregated way. To describe the aggregate behavior of traffic in cities, use is made of an idea that is now receiving some attention: the macroscopic fundamental diagram (MFD). We demonstrate through simulation how the MFD can be used to monitor and control a real network, in this case a portion of San Francisco, using readily available input data. We then show how different modes interact on the same network and discuss how these interactions might be incorporated into an MFD for multimodal networks. The work unveils two...

Multimodal Transport in Nairobi, Kenya: Insights and Recommendations with a Macroscopic Evidence-Based Model

Gonzales, Eric J.
Chavis, Celeste
Li, Yuwei
Daganzo, Carlos F.
2011

The limited street network in Nairobi, Kenya, is crowded with cars and matatus (informal transit). This paper studies the existing traffic performance using traffic simulation. Despite the poorly connected, asymmetric street network, there is a consistent relationship between aggregated traffic variables for the city center, namely the number of vehicles circulating in the network and the rate at which trips reach their destinations. This relation is called a macroscopic fundamental diagram (MFD), and shows how the capacity of Nairobi's streets compares to the capacity of streets in...