The re-distributional effects of an area traffic control policy
Abstract
The purpose of this paper is fourfold: to point out that the assessment of the benefits of an ATC scheme cannot be made properly without consideration of the re-distributional effects; to emphasise the importance of the interaction between ATC signal plans and traffic flow patterns; to show that the continual optimisation of signal plans can lead to a gradual deterioration of the network performance; and to demonstrate that traffic management measures (such as the banning of turning movements and the introduction of one-way schemes), and route control ideas, can be applied in conjunction with ATC policies to improve the performance of a network.
... In the 1970s, Allsop and Buckley 91974) developed one of the first theoretical formulations of a CRCM, thereby showcasing the impact of traffic signal controls on route choice. The theoretical framework of CRCMs was further evaluated by Maher and Akcelik (1975), Gartner and Florian (1976), and Allsop and Charlesworth (1977), who considered the effects of traffic signal controls on drivers' route choices. Smith (1979Smith ( , 1981aSmith ( , 1980Smith ( , 1981b conducted tests on a traffic signal control policy that relied on the existence of equilibrium in a traffic system. ...
Rapid increases in Saudi Arabia’s vehicular traffic are challenging its urbanized road networks’ safe and efficient operation. Facing both physical and economic constraints, transportation planning stakeholders in the country are seeking alternative methods for improving traffic operations and safety systemwide that do not rely upon infrastructure expansion. Using a sector of the Dammam metropolitan area in Saudi Arabia as the study area, we proposed and evaluated a comprehensive, integrated approach to improve both traffic system operations and
safety in this urbanized road network. A combined route choice and control modeling framework was used to evaluate the potential systemwide benefits of concurrent driver information regarding the best available route and traffic signal control enhancements to facilitate operational improvements. Benefits were quantified as improvements in total systemwide travel times and reduction in total systemwide delays. To evaluate associated road safety improvements, a comprehensive road safety audit (RSA) was performed in the study area and
Highway Safety Manual crash prediction methods were applied to estimate the potential reduction in crashes. Results indicated that concurrent driver information and an upgrade to vehicle-actuated traffic signal controls could improve total systemwide travel time by 22% and reduce the total systemwide delay by over 50%. If appropriate remediation measures are taken to address issues identified during the road safety audit, crashes could be reduced by up to 50 % per year at selected intersections. The study results infer that road safety improvements should be an integral part of any broader traffic systems improvement process and that the con-
current consideration of both traffic system operations and safety could provide the best return on investments. Further research could identify additional variables for consideration in the proposed comprehensive, integrated traffic systems improvement process and evaluate the transferability of this approach using a larger road network than the one considered in this study.
... Allsop based on his investigation was first to suggest that the traffic controls can impact the route choices of drivers [Allsop, 1974]. Maher and Akcelik [Maher and Akcelik, 1975], Gartner [Gartner, 1976], and Allsop and Charlesworth [Allsop and Charlesworth, 1977] investigated the joint route choice and control research problem on a theoretical level. Smith [(Smith, 1979), ], and Shefi and Powell [Shefi and Powell, 1982] investigated the problem for equilibrium. ...
Combined Traffic Assignment and Control (CTAC) models have been the topic of academic research
for the last three decades. The research problem has been explored by several researchers for solution
algorithms, model formulations, and implementation efforts. Although proven in academic research,
the use of CTAC models is rare in engineering practice. The practice tends to ignore the interaction
between drivers’ route choices and controls by keeping the traffic assignment and traffic control
optimization processes separate. Previous research emphasizes that CTAC models should be used in
practice as they can capture the control-driver interaction very well. The paper presents the benefits of
capturing interaction between drivers’ route choice and traffic controls. The benefits were computed in
terms of providing the drivers with network travel time information from past travel experience with
improvements in traffic controls. Six scenarios were tested on Park City, Utah road network using
Static and Dynamic Assignments with Fixed-Time, Vehicle Actuated, and Adaptive Traffic Controls.
The results show that the improvements of traffic controls to Adaptive Controls alone can substantially
reduce total delays and improve total-travel time. Across the six scenarios, the total delay reductions
and total travel time improvements were the highest for the traffic system when the drivers had network
travel time information from past travel experience with signal-controls improved to Adaptive
Controls. Further experiments are needed to compare the benefits for larger regional networks and
other simulation software.
... Allsop [5] suggested that the traffic controls impact route choice. Maher and Akcelik [6], Gartner [7], and Allsop and Charlesworth [8] investigated CTAC on a conceptual level by studying the use of signal control to influence route choice. Dickson [9], Smith [10,11], Shefi and Powell [12], and Marcotte [13] investigated the problem for the existence of equilibrium. ...
... Merge delay occurs on the ramp when an automobile waits for an acceptable gap in the freeway flow. It is reasonable to assume that the automobiles on the ramp wait for a gap of length D; thus, we can calculate the average merge delay from the queuing theory for (M/M/1) queues as {</>'/[exp(pD)-I] -rp\-1 (9) where ¢' =freeway curb-lane flow that inhibited the merge process and p' = vehicular density in that lane. If we combine transit time, metering delay, and merge delay, the average travel time on a freeway entrance ramp is ...
A program for optimizing most of the significant traffic engineering quantities while allowing for the fact that drivers can and do change their routes and modes of travel is proposed. The program requires the person origin-destination table as input and gives the best traffic-signal settings, reserved-lane assignments, and ramp-metering rates as outputs. the optimization can be for minimum person time, for minimum fuel consumption, or for a combination of both. The optimization was coded by using arbitrary but reasonable models for the components and run for a hypothetical network. Sample results are given.
We define potential energy function to measure traffic congestion and prove its rationality. Then we propose a bi-objective optimization model for the traffic guidance and control coordination based on eliminating congestion and minimizing the total traveling time. We realize the equilibrium of flow of network in a certain time by properly loading and unloading traffic flow volume and short- step adjustment for signal timing. This paper presents the detailed steps of algorithm of solving the quasi-optimal of the model. The coordinated algorithm is tested in the network built by software VISSIM. The simulation results show that the mean potential energy, mean-variance and mean traveling time gradually decrease after coordinations.
In order to prevent congestion of local road network which often leads to large scale road network over-saturation, the over-saturation states of road sections and road network were analyzed, and the method of road network over-saturation judgment and the method of ripe time judgment to trigger the guidance and control strategy were proposed. Based on graphic theory, the traffic guidance model was established under fixed traffic demand, taking the maximum saturation minimization as the objective, capacity and link flow balance as constraints. Traffic control model was established taking the link saturation variance minimization as the objective and link capacity and maximum phase time incremental as constraints. The models were solved by use of Genetic Algorithm. The experiments on case road network reveal that traffic guidance leads to reduction of maximum link oversaturation by 19.6%, and traffic control model leads to equilibrium of the saturation of each link the reduction of variation by 12.9%. As a result, the collaboration of traffic guidance and traffic control can significantly improve the performance of road network. To certain extent, the model can prevent large scale oversaturation and congestion of road network.
The regional travel demand models are generally macroscopic in nature and do not include traffic controls in the traffic assignment process. In travel demand models, the road capacities are kept fixed within the functional classification of roadways and free-flow-speeds are adjusted to accommodate the impacts of traffic controls and traffic operations. Part of the reason this approach is adopted in travel demand models is there macroscopic application, where the focus is extensively on the region wide results for transportation planning. While there are advantages in using this approach, the cost is usually paid in "lost capacity on projects" due to the absence of traffic operations in modeling; more precisely the absence of traffic controls tend to present partially skewed output from the travel models. Combined Traffic Assignment and Control models can address this issue by including the impacts of traffic controls in the modeling process. This paper evaluates the benefits of combined traffic assignment and control modeling framework implemented on a regional scale compared to a traditional four step regional travel demand model. The study quantifies the benefits in terms of providing network travel time information to drivers to make route choice in comparison to improving the traffic controls on a large regional network (on a mesoscopic level). Several experiments were performed on a study area using Static Traffic Assignment (STA) and Dynamic Traffic Assignment (DTA) with fixed and vehicle-actuated controls. The study area network is a regional transportation network for the Wasatch Front Region in Utah. The results suggest that if implemented on regional travel models, the CTAC framework can help reduce the VMT and reduce regional delays by over 6%. Further studies are needed to expand on this idea with multimodal modeling and testing on other regional networks.
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