11-14 Dynamic Variable Speed Limit Control: Design, Analysis and Benefits

Project Number


Project Summary

Dynamic Variable Speed Limit Control: Design, Analysis and Benefits

Project Status


Project Report



Topic Area

Urban Mobility

P.I. Name & Address

Professor of Electrical Engineering Systems, Ming Hsieh Department of Electrical Engineering; USC Viterbi School of Engineering
University of Southern California
3740 McClintock Avenue
Hughes Aircraft Electrical Engineering Center (EEB) 200B
Los Angeles, CA 90089-2562
United States

Project Objective:

The use of variable speed limits (VSL) along highway lanes in an effort to control traffic flow is a technique that has been around for some time. It has been implemented in various parts of Europe and has been studied by several researchers during the recent years. The incentive of using VSL has been mainly safety from the application point of view but benefits such as improved traffic flow rates, lower travel times, smooth speed and density distribution and possibly lower pollution have been conjectured in literature and in some cases analyzed using mainly macroscopic traffic models. The use of aggregate flow or macroscopic models and optimization techniques to develop and test these dynamic VSL controllers (which can be activated during incidents or other disruptions) has led to optimistic results in terms of lowering travel times, sometimes by as much as 20%.

However, a closer look at these results shows that using the same macroscopic model to design and test VSL controllers raises questions as to whether the simplicity of the models used for evaluation are responsible for these optimistic results given the fact that other studies using microscopic simulations fail to demonstrate improvements on travel times, albeit for different VSL strategies. The question of whether the VSL strategies, or the macroscopic models used to analyze them, or both are responsible for the large differences (not only quantitative but also qualitative) in traffic flow and travel time benefits reported, remains unanswered. Consequently, the problem of what are the most appropriate dynamic VSL controllers and what benefits can be guaranteed in a consistent manner under different traffic flow conditions is an open one.

This research capitalizes on past results obtained from modeling and traffic flow analyses. It addresses the design, analysis, and evaluation of dynamic VSL controllers. A control engineering approach is used, in which the control strategies are designed based on simplified models (validated macroscopic traffic models, in this case), but applied and tested on validated microscopic traffic models under different traffic conditions. The dynamic VSL control design will be based on optimizing travel times, smoothness of traffic, environmental impacts, and, indirectly, safety. Macroscopic traffic models and microscopic simulation models based on VISSIM of large sections of I-110 and I-710 in Los Angeles County will be used as examples for design and evaluation. The I-110 has several bottlenecks where VSL control may help during peak hours and I-710 has a high volume of trucks serving two major ports which will allow us to examine the impact of truck traffic on VSL. Data from California's Performance Measurement System (PeMS) and other sources will be used to validate the macroscopic and microscopic simulation models.

The evaluation of the dynamic VSL control strategies will be based on comparison of the benefits in terms of traffic flow, travel times, smoothness of traffic, number of lane changes, and environmental impacts with control and without control under different traffic conditions which will include bottlenecks, incidents, and high/low peak traffic situations. The modal emissions model developed by the research group at the University of California at Riverside for different classes of vehicles will be used to measure fuel consumption and pollution levels for all vehicles in the network in order to assess the environmental impacts of different VSL strategies. Monte Carlo simulations will be performed in order to reduce the effect of random errors and check the consistency of results.

Task Descriptions:
(1) Macroscopic and microscopic simulation models for I-110 and I-710
(2) Dynamic Variable Speed Limit control
(3) Analysis and evalutation of dynamic VSL using the macroscopic models
(4) Evaluation of dynamic VSL using the microscopic simulation models
(5) Potential for application and implementation issues

Milestones, Dates:
(1) August 2010 – December 2010
(2) January 2011
(3) February 2011 – March 2011
(4) April 2011 – May 2011
(5) June 2011 – July 2011

Total Budget:

Student Involvement:
One graduate student at 50% effort, 9 months

Relationship to Other Research Projects:
Related to 08-04, 09-11; part of goods movement and mobility focus area

Technology Transfer Activities:
Project report will be posted soon

Potential Benefits of the Project:
Improve speed, travel time, environmental impacts, and safety on highways

TRB Keywords:
Freight Transportation, Highways, Operations and Traffic Management

Primary Subject:
1p.1 To design, analyze and evaluate using extensive macroscopic and microscopic traffic simulation studies, dynamic variable speed limit control strategies.