ITS Berkeley

Presignal Used to Increase Bus- and Car-Carrying Capacity at Intersections: Theory and Experiment

Xuan, Yiguang (Ethan)
Gayah, Vikash V.
Cassidy, Michael J.
Daganzo, Carlos F.
2012

In theory midblock presignals can be used to increase the capacity of signalized intersections [The authors define “presignal” as “a set of signal heads that are installed in the middle of a block upstream of an intersection.”—Ed.]. The capacity is increased because presignals can reorganize how traffic is stored between a presignal and an intersection downstream. However, different vehicle classes have different acceleration characteristics, and the effectiveness of presignals hinges on the assumption of linear superposition; that is, the total time to discharge a mixture of distinct...

Dual Influences on Vehicle Speed in Special-use Lanes and Critique of US Regulation

Jang, Kitae
Cassidy, Michael J.
2012

We verify that slow speeds in a special-use lane, such as a carpool or bus lane, can be due to both, high demand for that lane and slow speeds in the adjacent regular-use lane. These dual influences are confirmed from months of data collected from all freeway carpool facilities in the San Francisco Bay Area. Additional data indicate that both influences hold: for other types of special-use lanes, including bus lanes; and for other parts of the world. The findings do not bode well for a new US regulation stipulating that most classes of Low-Emitting Vehicles, or LEVs, are to vacate slow-...

A Capacity-Increasing Mechanism in Freeway Traffic

Kim, Kwangho
Cassidy, Michael J.
2012

A reason is unveiled for the time-varying pattern in discharge flow that is commonly observed at freeway bottlenecks. We hypothesize that four known effects in freeway traffic can interact upstream of a bottleneck in ways that trigger periodic bursts in its discharge flow. Repeated observations of a 3-km freeway stretch support the hypothesis. Controlled experiments show that the capacity-increasing mechanism can be favorably modulated by metering the site’s on-ramps in an unconventional manner. The unconventional strategy repeatedly produced higher average discharge flows and shorter on-...

Inhomogeneous Flow Patterns in Undersaturated Road Networks: Implications for Macroscopic Fundamental Diagram

Doig, Jean C.
Gayah, Vikash V.
Cassidy, Michael J.
2013

Travel conditions on a road network are described by a macroscopic fundamental diagram (MFD) only when traffic is homogeneously distributed over all of the network's links. Otherwise, a network's measured traffic states fall beneath its MFD, and network flow therefore falls below the maximum. The present study found that inhomogeneous link flowed in a network may emerge before the beginning of a peak period, even before persistent queues had formed. This finding is potentially problematic because it is known that inhomogeneities of this kind can persist in a network for long durations....

Mitigating Negative Impacts of Near-Side Bus Stops on Cars

Gu, Weihua
Cassidy, Michael J.
Gayah, Vikash V.
Ouyang, Yanfeng
2013

Bus stops are often placed short distances upstream of signalized intersections. Buses that dwell at one of these so-called near-side stops can impede queued cars upstream from discharging through the intersection during green times. Residual car queues can form at the intersection as a result. The smaller the distance between a stop and its intersection, the greater the problem can be. Models are formulated to address this problem using kinematic wave theory. The models can be used to determine where to place a near-side stop to achieve a target level of residual car queueing. In addition...

Collisions in Freeway Traffic: Influence of Downstream Queues and Interim Means to Address Them

Li, Zhibin
Chung, Koohong
Cassidy, Michael J.
2013

Findings from previous studies indicate that a freeway traffic collision is more likely to occur in close physical proximity to the tail of a queue. The implication is that collision likelihood increases when drivers abruptly alter their trajectories (e.g., by decelerating or changing lanes) on encountering the queue. The implication is supported and bolstered with new and detailed data that were painstakingly extracted from two freeway stretches in California. These data show how the likelihood of collision increases as both the spatial and the temporal proximities to the tail of an...

Maximizing Bus Discharge Flows from Multi-Berth Stops by Regulating Exit Maneuvers

Gu, Weihua
Cassidy, Michael J.
2013

Upon having loaded and unloaded their passengers, buses are often free to exit a multi-berth bus stop without delay. A bus need not wait to perform this exit maneuver, even if it requires circumventing one or more other buses that are still dwelling in the stop’s downstream berths. Yet, many jurisdictions impose restrictions on bus entry maneuvers into a stop to limit disruptions to cars and other buses. Buses are typically prohibited from entering a stop whenever this would require maneuvering around other buses still dwelling in upstream berths. An entering bus is instead required to...

Access and the Choice of Transit Technology

Sivakumaran, Karthik
Li, Yuwei
Cassidy, Michael
Madanat, Samer
2014

An urban transit system can be made more cost-efficient by improving the access to it. Efforts in this vein often entail the provision of greater mobility, as when high-speed feeder buses are used to carry commuters to and from trunk-line stations. Other efforts have focused on the creation of more favorable land-use patterns, as occurs when households within a Transit-Oriented Development (TOD) are tightly clustered around trunk stations. The efficacy of these mobility and land-use solutions are separately examined in the present work. To this end, continuum approximation models are used...

On the Impacts of Bus Stops near Signalized Intersections: Models of Car and Bus Delays

Gu, Weihua
Gayah, Vikash V.
Cassidy, Michael J.
Saade, Nathalie
2014

Models are formulated to predict the added vehicle and person delays that can occur when a bus stop is located a short distance upstream or downstream of a signalized intersection. Included in the set of models are those that predict the expected delays that cars collectively incur when a bus blocks one of multiple lanes while loading and unloading passengers at the stop. Others in this set predict the expected added delays incurred by the bus due to car queues. Each model is consistent with the kinematic wave theory of highway traffic, as is confirmed through a battery of tests. And each...

Continuum Approximation Approach to Bus Network Design under Spatially Heterogeneous Demand

Ouyang, Yanfeng
Nourbakhsh, Seyed Mohammad
Cassidy, Michael J.
2014

A methodological framework is formulated so that continuum approximation techniques can be used to design bus networks for cities where travel demand varies gradually over space. The bus-route configurations that result consist of (i) a main, possibly city-wide grid with relatively large physical spacings between its parallel routes and the stops along those routes; together with (ii) one or more local grids with more closely-spaced routes and stops that serve neighborhoods of higher demand densities. The so-called power-of-two concept is borrowed from the field of inventory control, and...