Project Progress Report
Ramp Metering in Freeway System
Submitted To:
The 2014 Summer NSF REU Program
Sponsored By:
The National Science Foundation
Grant ID No.: DUE – 0756921
College of Engineering and Applied Science
University of Cincinnati
Cincinnati, Ohio
Prepared By:
Emma Hand, Civil Engineering, University of Cincinnati
Jared Sagaga, Computer Science, University of Cincinnati
Isaac Quaye, Aerospace Engineering, University of Cincinnati
Report Reviewed By:
Heng Wei, PhD, PE, EIT
REU Faculty Mentor
Associate Professor
Department of Civil and Architectural Engineering and Construction Management
University of Cincinnati
June 20, 2014
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Abstract
In 2013, traffic congestion cost commuters in the U.S. approximately $101 billion in lost time
and wasted fuel.
Local governments and transportation agencies have used a variety of
mitigation strategies to reduce the cost of traffic congestion. This report examines one such
strategy, ramp metering. Using a modelling approach to evaluate the various types of metering,
we will be taking into consideration various components such as operational characteristics, the
ramp meter system in effect, and the amount of lanes on the on-ramp. The key element of
deploying a ramp metering system is to control the traffic entering the freeway mainline, with the
intent to reduce congestion and in turn reduce travel times and ensure the safety of motorists.
Data collected during this project along with previously gathered data will be used to create
traffic simulations using the micro simulation software VISSIM, and to determine the
effectiveness of the placement of these meters.
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Introduction
Ramp metering systems are traffic devices used to control traffic entering the freeway
mainline. Ramp meters are being used in states such as Arizona, Michigan, Minnesota
and others, and have been shown to successfully regulate the flow of traffic on the
freeway in order to reduce congestion, collisions and travel times to destinations.
Different types of metering systems are used in differing situations, and each has its own
benefits and drawbacks, including maintenance costs and ease of use. Ramp meters have
been under development for decades, and have been proven in many cases to be
successful, with benefits far outweighing any drawbacks. Departments of Transportation
(DOT) in several states have performed tests which have proven the effectiveness of
ramp meters, and have included the voice of the public in meter installation projects in
order to gain the acceptance of residents and others who will be affected by the metering
systems.
While ramp meters have been proven to be successful, there are some
limitations to these systems. They are very expensive to implement and maintain, and
complicated algorithms are used that will render ramp meters ineffective if there are any
errors. Isolated ramp meters fail to detect upstream or downstream traffic flows, which
can result in serious traffic congestions when there is sudden traffic change. Regardless
of these limitations, ramp meter strategies are expanding nationwide.
Background Literature Review
Ramp Meters in Different States
Several states around the country use ramp metering to control traffic, increase freeway
safety, reduce travel time and maximize freeway throughput.
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Some of these states
include Minnesota (433 ramp meters), Arizona (300 ramp meters), California (1,000
ramp meters), and Washington (280 ramp meters) (Minnesota Dept. of Transportation;
Arizona Dept. of Transportation; California Dept. of Transportation; Jacobson, Stribiak,
Nelson, Sallman). The types of ramp meters used vary from state to state. In Minnesota,
depending on the ramp and traffic conditions, either fixed time or responsive ramp meters
are installed, and are monitored throughout the entire state in a single system containing
many sub-systems (Jacobson, Stribiak, Nelson, Sallman). In Washington, responsive
traffic meters and fuzzy logic are used to run the ramp metering system statewide
(Jacobson, Stribiak, Nelson, Sallman).
The introduction of ramp metering to Minnesota and Washington brought about several
benefits, but also presented each state with some difficulties during the implementation of
the metering systems.
Some of the difficulties that were faced by each state’s
Department of Transportation about ramp metering include:

Poor performance in inclement weather or during special events

Vehicle queues force overrides causing the algorithms to restart

Staffing, training, and ramp metering implementation

Complete acceptance by the public

Poor marketing of its benefits and high reciprocity at a low expense
The Departments of Transportation in Minnesota (Mn/DOT) and Washington (WSDOT)
are still facing these issues today (U.S. Dept. of Transportation).
With technology
improving every day, however, the difficulties are not as severe as when ramp metering
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was first introduced onto these states’ freeways.
These difficulties can also cause
decisions on ramp metering installation to take some time, especially if public input is
needed to make the decisions. Washington includes the public in its ramp metering
program, with public outreach and disseminating information being vital to any planning
of ramp metering installation (Jacobson, Stribiak, Nelson, Sallman). Minnesota has also
implemented this type of method into their future plans for proposed ramp metering
installations after performing an evaluation in 2001 on their ramp metering system in
Twin Cities.
Uses of Ramp Metering
According to the FHWA (Federal Highway Administration),
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Ramp meters are used to regulate and reduce traffic volume on freeways by spreading
out queues of vehicles over a period of time.
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Reduced traffic congestions are a result of traffic meters, increasing freeway speeds
and thereby improving travel time and travel time reliability.
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Metering systems help lessen crashes on freeways around the entrance ramps, in
effect ensuring the increased safety of motorists.
Types of Ramp Metering
There are different types of ramp metering systems that are put in place, each with its
own benefits and limitations.
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Fixed Ramp Metering
Fixed Ramp Meter systems, also called Pre-timed Ramp Meter systems, operate on a
fixed ramp cycle, or period of time that the meter goes through the colors red and green.
This pre-timed meter cycle is based off of data from past traffic conditions, assuming the
patterns of these conditions are fairly constant from day to day (Kang). Different meter
cycles are used depending on how many cars are intended to pass through. A system
designed to break up platoons, or large groups of vehicles, has a cycle between four to
seven seconds, with meter rates lasting just long enough for one or two cars to pass
through at a time. During times of the day when traffic is not expected to be as busy,
cycles last ten seconds or more allowing three or more vehicles to pass at a time. In the
present study, the cycle used for the single lane on ramp will be four seconds and the
cycle for the two lane ramp will be 6.56 seconds.
Benefits
Fixed ramp meter systems have low maintenance costs, and provide drivers with a
reliable pattern to which they can easily adjust (Kang). The pre-timed systems provide
benefits associated with reduced congestion. Travel time and side-swipe accidents that
happen when incoming traffic merges onto the mainline freeway are lessened, while
throughput, or the lack of traffic stand-stills, is increased.
Limitations
Fixed meter cycles do not respond to any traffic conditions on the freeway mainline,
remaining unaltered even if there are sudden fluctuations in the traffic. There can also be
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a problem with fixed meter systems when the amount of vehicles on the on-ramp reaches
capacity, because traffic enters the on-ramp at a greater rate than the meter allows traffic
to access the freeway.
Traffic Responsive Ramp Metering
The meter cycles of responsive ramp meters are based on real-time measurements from
sensors installed along the freeway network shown in Fig. 1. The mainline loops give the
occupancy of the mainline traffic. The passage loop gives the count of vehicles that pass
through the meter. The demand loops relay to the meter when there are vehicles waiting
to enter the freeway; when these sense no vehicles, the meter remains red. The queue
loop senses how many vehicles enter the on-ramp and whether it is full. All of these
factors contribute to the meter’s determining of the meter rate. These meter systems can
be either local or coordinated. The local ramp metering method uses measurements from
an area around a single ramp whereas the coordinated ramp metering system uses data
from the entire network. Sites have differing traffic conditions, and based on these
conditions an apt algorithm is used. Depending on the algorithm used, coordinated
responsive systems either sense only traffic from local arterials, streets by the highway,
or communicate with meter systems on adjacent ramps. (Papamichail I., and
Papageorgiou, M.)
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Figure 1. Responsive ramp metering system diagram
Benefits
The local and coordinated ramp metering strategies have proven to be more efficient than
the fixed traffic ramp meters because of the sensors that communicate between the
freeway and the ramp meters. There are no backups onto local arterials due to the sensor
at the entrance to the on-ramp. Sensors detecting the current traffic conditions on the
mainline freeway allow the meter to change its rates accordingly. The traffic responsive
strategy is a better regulator of traffic from the ramp joining the freeway.
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Limitations
Coordinated ramp meter systems are extremely complex, and thus very expensive to
install and maintain. Isolated systems do not take into account the traffic upstream or
downstream of the on-ramp. This can cause problems if sudden traffic changes occur
further out than the isolated system senses, and the ramp meter allows too much traffic to
enter the freeway. (Papamichail I., and Papageorgiou, M.)
Goals and Objectives
The objectives of this project are to investigate and understand the effectiveness of ramp
metering placements, and determine the number of installments needed on a stretch of
highway. The effects of single and two lane ramp metering implementation will be
observed, through data collected from I-275 and US-42 Lebanon Road during peak
periods, simulations created by the group in VISSIM, and information gathered from
several other sources.
Scope of Study
The main focus of this research will be on the traffic conditions at a single lane on-ramp
without a ramp meter, and both single and two lane on-ramps with ramp meters.
The selection of the sites should meet the following criteria:
1) There are elevated locations nearby for placing the camcorder to capture the traffic.
2) Location should be busier in the peak hours than the normal flow of freeway.
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Based on the above criteria, the I-275 and US- 42 Lebanon road intersection is the chosen
study site selected for the current research. Video data will be collected and postprocessed using a traffic counter, and a GPS device will be utilized while driving on a
given stretch of the road during peak hours of the day. Traffic flow on the freeway
mainline, on-ramp, and arterials will be observed, and both a single and two lane ramp
implementation will be investigated. Information gained from the observations of these
on-ramps will be analyzed in order to determine which type of ramp metering is most
effective and efficient. The gathered data will be used to create simulations of possible
real-world scenarios in VISSIM. The simulations will also aid in the investigation of
future implementation of ramp metering.
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References
Arnold, Jr., E. D. (1998). “Ramp Metering: A Review of the Literature,” Technical Assistance
Report No. VTRC 99-TAR5, Virginia Transportation Research Council, Charlottesville, Virginia.
Department of Transportation, California (2007). "Why Are There Signals Installed at Some
Freeway Onramps?" Why Are There Signals Installed at Some Freeway Onramps? Web. 16 June
2014.
Department of Transportation, Minnesota (2011). "Ramp Meters." Minnesota Department of
Transportation. Web. 16 June 2014.
DeWelles, Angela (2011). "ADOT Blog: Getting the Green Light: Valley Ramp Meters Now
More Efficient." ADOT Blog: Getting the Green Light: Valley Ramp Meters Now More
Efficient. Web. 16 June 2014.
Federal Highway Administration (2013). "Ramp Metering Presentation." Localized Bottleneck
Reduction Program. US Department of Transportation. Web. 16 June 2014.
Jacobson, Leslie N., Jason Stribiak, Lisa Nelson, and Doug Sallman (2006). "Chapter 11 - Case
Studies." Ramp Management and Control Handbook. Washington, DC: U.S. Dept. of
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Kang, S., Gillen, D. (1999). “Assessing the Benefits and Costs of Intelligent
Transportation Systems: Ramp Meters,” California PATH Research Report No. UCB-ITS-PRR99-19, Institution of Transportation Studies, University of California, Berkley, California.
Arizona Department of Transportation. (2003). Ramp Meter Design, Operations, and
Maintenance Guidelines.
Papamichail I., and Papageorgiou, M. (2008). “Traffic-Responsive Linked Ramp-Metering
Control,” IEEE Transactions on Intelligent Transportation Systems, Vol. 9, No. 1, n.p.
State of California Department of Transportation. “Ramp Metering In Caltrans District 7 (Los
Angeles and Ventura Counties).” 2005.
Yu, G., Recker, W., Chu, L. (2009). “Integrated Ramp Metering Design and Evaluation Platform
with Paramics,” California PATH Research Report No. UCB-ITS-PRR-2009-10, Institution of
Transportation Studies, University of California, Berkley, California.
Zongzhong, T., Nadeem, A. C., Messer, C. J., Chu, C. (2004). “Ramp Metering Algorithms and
Approaches for Texas,” Transportation Technical Report No. FHWA/TX-05/0-4629-1, Texas
Transportation Institute, The Texas A&M University System, College Station, Texas.
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