Recent its_future_urban_transport items

Traffic Congestion in Networks, and Alleviating it with Public Transportation and Pricing

Wed, 30 Apr 2025 00:00:00 +0000

It has recently been demonstrated, both theoretically and experimentally, that the average flow and density of some urban traffic networks is related by a unique, reproducible curve known as the Macroscopic Fundamental Diagram (MFD). For networks in which vehicles cannot adaptively re-route to avoid congestion, this relationship is robust only when there are few vehicles on the network. As these types of networks become more crowded, trips are completed at a much lower rate than predicted by MFD theory. Thus, operating a network in congestion is extremely damaging on these networks. The damage is particularly harmful for networks in which multiple modes operate mixed together because the more efficient modes, such as public transportation, suffer from the congestion created by other vehicles. This tends to happen in cities when infrastructure development has not caught up with economic development; one example that we have observed is Nairobi, Kenya. One way to increase efficiency...

Advancing Bus Rapid Transit and Transit Oriented Corridorsin California’s Central Valley

Wed, 14 Oct 2020 00:00:00 +0000

This study explores possibilities for advancing bus rapid transit (BRT) systems and associated higher density land development in the Central Valley of California. It uses photo-simulations and stakeholder reactions to visual images to gauge public attitudes toward what would be a fairly radical transformation of urban environments in traditionally car-oriented settings.The kinds of transformations that would be needed to economically justify higher quality BRT services will likely require better and more frequent bus as well as amenities in the form of street trees, landscaping, street furniture, improved building facades, bike lanes, and the like. By eliciting views and responses from local stakeholder interests about BRT service design and surrounding development patterns, the work sought to provide a platform for stimulating open public dialogue on factors that could be vital to successful project implementation.

Effects of HOV Lanes on Freeway Bottlenecks

Mon, 5 Oct 2020 00:00:00 +0000

In this paper, the authors report on research that shows that high occupancy vehicle (HOV) lanes do not reduce the capacity of general purpose (GP) lanes. Empirical evidence, complemented with simulations, enable the authors to describe how to estimate total bottneleck capacity and how deploy HOV lanes without hindering vehicle flow. The authors also offer a dynamic strategy that increases a bottleneck's total discharge rate.

Macroscopic Relations of Urban Traffic Variables: An Analysis of Instability

Mon, 5 Oct 2020 00:00:00 +0000

For networks consisting of a single route the Macroscopic Fundamental Diagram (MFD) can be predicted analytically; but when the networks consist of multiple overlapping routes the flows observed in congestion for a given density are less than those one would predict if the routes were homogeneously congested and did not overlap. These types of networks also tend to jam at densities that are only a fraction of their routes’ average jam density. This paper provides an explanation for this phenomena. It shows that, even for perfectly homogeneous networks with spatially uniform travel patterns, symmetric equilibrium patterns with equal flows and densities across all links are unstable if the average network density is sufficiently high. Instead, the stable equilibrium patterns are asymmetric. Analysis of small idealized networks that can be treated as simple dynamical systems shows that these networks undergo a bifurcation at a network-specific critical density such that for lower...

The Environmental Impacts of Logistics Systems and Options for Mitigation

Mon, 5 Oct 2020 00:00:00 +0000

This paper presents a discussion directed at determining the most progressive options for shifting the freight logistics industry towards having more sustainable-oriented goals. The authors first discuss transportation sustainability and the concept of green logistics. This is followed by a discussion on externalities resulting from vehicle emissions and indirect environmental externalities. The problem of environmental externalities is then examined, with focus on emissions and other related data. The authors then examine options for reducing environmental externalities. They discuss impact considerations, options focused on emissions reduction, changing freight sector operations, and considerations regarding demand and economic development.

Urban Development on Railway-Served Land: Lessons and Opportunities for the Developing World

Mon, 5 Oct 2020 00:00:00 +0000

Under the right conditions -- serious traffic congestion, a permissive regulatory environment, and frequent and reliable transit services -- rail transit investments can powerfully shape cities and regions. Rail transit’s city‐shaping powers are due to market forces and policy interventions. By enhancing accessibility (the ability of those living, working, or shopping rail near stops to quickly reach desired destinations) rail services increase the value and desirability of properties in and around stations. Market pressures by themselves rarely produce transit oriented development. To leverage private investments in and around stations, pro‐activism and a certain amount of risk‐taking on the part of local governments are often needed. This report includes case studies from several cities, along with a policy lessons summary. Land value impacts and value capture opportunities are described.

Exploring the Effect of Turning Maneuvers and Route Choice ona Simple Network

Mon, 5 Oct 2020 00:00:00 +0000

A simple symmetric network consisting of two tangent rings on which vehicles obey the Kinematic Wave Theory of traffic flow and can switch rings at the point of tangency is studied. An online adaptive simulation reveals that if there is any turning whatsoever the two-ring system becomes unevenly loaded for densities greater than the optimal density. This reduces flow. Furthermore, the two-ring system jams at significantly lower densities than the maximum density possible.

On the Design of Public Infrastructure Systems with ElasticDemand

Mon, 5 Oct 2020 00:00:00 +0000

This paper considers the optimization of public infrastructure systems, recognizing that these systems serve multiple user classes. Under the guidance of a policy-making body, the analyst chooses both the system design, including its layout and control, and the prices to be charged for the service. The goal of the optimization is to maximize society's welfare recognizing that the system's performance will in general depend on the system's demand, and vice versa. The optimization problem is first formulated in its full complexity. Under defined circumstances, the problem decomposes into three sub-problems that can be solved sequentially. The resulting design is independent of how net user benefits are measured. If the policy-making body does not specify cost or demand targets, and instead assesses benefits by means of consumer surplus then the optimum design is still the solution of a conventional design problem with fixed demand. In this case, however, the demand has to be obtained...

On the Stability of Freeway Traffic

Mon, 5 Oct 2020 00:00:00 +0000

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 of flow and density quickly becomes uneven. The flow-density deviations from the average are shown to grow exponentially in time and propagate backwards in space with a fixed wave speed. A consequence of this type of instability is that, during recovery, gaps of uncongested traffic will quickly appear in the unevenly congested stream, reducing average flow. This extends the duration of recovery...

On the perceptibility of safety systems

Mon, 5 Oct 2020 00:00:00 +0000

The perceptibility of a safety system is defined as the extent to which the system can be perceived by the senses or the mind. The objective here is to study which safety systems are more easily perceived by the user and to identify design attributes that affect this level of perception. A web-based, pairwise comparison survey was conducted to evaluate the perceptibility of fifteen safety systems ranging from traffic safety systems to consumer safety. The analytic hierarchy process was applied to estimate the perceptibility levels and rank the safety systems. The results show that protection systems that require activation are more perceptible than passive ones.

Urban Densities and Transit: A Multi-dimensional Perspective