Ramp Metering

Term Paper
Progress Report

Name: Naeem Rezghi
Student ID: 8722229076
Course: Traffic Engineering, CIV4116 -S12
Instructor: Mr. Peyman Misaghi
Date: J uly 1, 2012

T able of Contents
1- Introduction ..................................................................................................................... 3
2- History .............................................................................................................................. 4
3- Ramp Metering Algorithms .......................................................................................... 5
3-1- S ystem Architecture .............................................................................................. 5
3-2- Release Algorithm .................................................................................................. 6
3-3- A rbitration Algorithm .............................................................................................. 7
3-4- S witch On- Off Algorithm ....................................................................................... 8
3-5- Q ueue Override Algorithm .................................................................................... 9
3-6- Q ueue Management Algorithm ........................................................................... 9
3-7- Ramp Metering Algorithm ...................................................................................10
3-8- Data Filtering Algorithm: .....................................................................................10
4- Types of Ramp Metering ............................................................................................11
4-1- Local Ramp Metering ..........................................................................................11
4-2- Coordinated Ramp Metering ..............................................................................12
5- Design of Metered Ramps .........................................................................................13
6- Conclusion ....................................................................................................................17
7- References: ..................................................................................................................18

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Ramp Metering

1- Introduction
Ramp metering is one of the most important methods used for reducing traffic congestion. Ramp control, or ramp metering, has been defined as one of the most effective methods for preventing freeway congestion. The entering traffic to the freeway from on-ramps is regulated so that the flow on the freeway does not exceed the capacity. The ramp meter also helps break the “platoon” of entering vehicles, which created while merging operation.

The first practical experience of ramp metering control was on the
Eisenhower Expressway (I-290) in Chicago, Illinois, in 1963, that a police officer directed the traffic to allow one vehicle to enter at a time, at a predetermined rate.
Nowadays ramp metering has developed throughout the US, with applications in
Minnesota, California, New York, and Washington state. Also the usage of ramp metering system can be seen in European cities like Amsterdam, Paris, and
Glasgow.

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The most important benefits of using ramp metering system can be categorized as following:
 Controlling the traffic flow of freeways by temporarily storing the traffic flow in ramps to ensure that the express way is operated with its full capacity and without any reducing effects.
 To make a break line between different platoons of vehicles entering the freeway so that on ramp vehicles can easily merge to the main traffic flow on freeways.
 Divert some vehicles to other routes due to waiting time in order to reduce the demand of freeways.
In the following this paper will cover different techniques and algorithms of ramp metering systems and different types of ramp metering systems. Then a briefly design method for ramp metering systems will be discussed.

2- History
As it was discussed before, the first experience of ramp metering was in
Chicago in which a police officer who was positioned on the ramp was directly controlled the traffic flow on ramps, stopping vehicles and releasing them in a specific time at a predetermined rate. In United States ramp metering systems began from Los Angles and then gradually improved. There are now about 1,300 ramp metering devices in Los Angles.
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The first ramp metering devices were simple fixed -time ramp meters that their data collection was locally. But in last 30 years, with the improvement of technology, the complexity of ramp metering hardware and control algorithms enhanced, as they can provide a real-time analysis. The objective of these advanced ramp meters is to provide a data analysis plan which gathered from several ramps. These data plan will result in forecasting of mainline flow breakdowns, queue spillbacks pass the off-ramps, and queue spillbacks from entrance ramps into secondary road system.

3- Ramp Metering Algorithms
3-1- System Architecture
Ramp metering process uses negative feedback control loops as it can be seen in Figure 3.1. In this architecture the maximum flow of the main route, i.e. freeway, will remain constant without any disrupting in local routes.

By current architecture there are seven algorithms as following:
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 Release algorithm
 Arbitration algorithm
 Switch on-off algorithm
 Ramp metering algorithm
 Queue override algorithm
 Queue management algorithm
 Data filtering algorithm

3-2- Release Algorithm
The applications of release algorithm are as following:
 It sets the traffic signals for controlling the traffic flow.
 It monitors the actual release rate.
 It manages the transition from signal off to signal on, and vice.

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Figure 3.3 shows the schematic release algorithm.

3-3- Arbitration Algorithm
The arbitration algorithm manages the naïve data which need to be corrected with some adjustment factors. The output of ramp metering, queue management, queue override and switch on-off algorithms are the primary input to the arbitration algorithm. Then so me calibration processes will be done in arbitration algorithm and finally the correct data will output to the release algorithm. Figure 3.4 shows the schematic arbitration algorithm.

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3-4- Switch On-Off Algorithm
Switch on-off algorithm switches the ramp metering devices on or off. For this reason this algorithm has a constant minimum and maximum value. It switches on/off by monitoring the traffic flow, when minimum level of occupancy exceeds. Also it switched off or delays switch on while the flow speed is above the safe speed. Some definitions for this algorithm are:
 M anual On: When upstream line speed is low enough.
 M anual Off: Used for manually off the system.
 Timed: When the day and time maximum speed criteria are reached.
 Timed Occupancy: When the day and time minimum occupancy and maximum speed are reached.
 Timed Flow and Occupancy: When the day and time minimum flow and minimum occupancy are reached.
Figure 3.5 shows a schematic Switch On-Off algorithm.

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3-5- Queue Override Algorithm
In this algorithm the numbers of queues which are waiting to join the main traffic flow are reduced for preventing the adversely affect on local roads. An excessive queue number will be detected with this algorithm and the algorithm can reduce the waiting queue length by releasing the traffic immediately.
Figure 3.6 shows a schematic of Queue Override Algorithm.

3-6- Queue Management Algorithm
This algorithm controls the queue length to maximize the period of ramp metering operation and minimize the overriding of queue in ramp.
Figure 3.7 shows a schematic of Queue Management Algorithm.

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3-7- Ramp Metering Algorithm
This algorithm determines the optimum traffic flow for the main express way, so that the main way remain in its maximum capacity and local roads do not affect from the ramp waiting queues.
Figure 3.9 shows a schematic of Ramp Metering Algorithm.

3-8- Data Filtering Algorithm:
This algorithm calculates the smoothest values for flow, speed and occupancy from the raw data with regression models. Then the smoothed data will output to other algorithms as following:
 M ain carriageway data filtering algorithm: This algorithm take the smoothed data and calculates the smoothed flow, speed and occupancy for each loop pair at each loop site.
 Ramp data filtering algorithm: It inputs the smoothed data and calculates the number of vehicles passing each road loop to be used in queue estimation and control algorithms.

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4- Types of Ramp Metering
As a general categorization, there are two types of ramp met ering controls: local ramp metering and coordinated ramp metering.
4-1- Local Ramp Metering
Local ramp metering systems are the conventional types of ramp meters in which the devices have a pre -timed control. The set of local ramp meters is basically from methods presented in Highway Capacity Manual, but the modification of this basic data is nee ded for each condition. This system is designed to analyze the historical traffic patterns and to determine the quantity of freeways’ flow, but this method has some disadvantages. The main disadvantage of this system is that it cannot provide a data plan, so it cannot forecast changing conditions due to seasonal changing or daily dynamic flows.
Also there is another type of local ramp meters called “Local Traffic Responsive Control”. This type ,as like as simple local ramp meters, provide a local data series, but in opposed to normal ones, this system uses loop detectors to provide a small data p lan. Also this method is much better than the basic local ramp metering system, but it can cause problems during incidents due to lack of a data network plan. So that it may optimize the traffic flow in a small loop, but not for whole of the system.

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4-2- Coordinated Ramp Metering
This method provides a data plan for whole of the ramp systems, not for individual ramps, so that the optimization of traffic flow in entire ramps will be resulted. The coordinated ramp metering system is often considered as the b est method for controlling the traffic flow on entrance of freeways while it is the most expensive and sophisticated ramp metering system. In this system the traffic flow data will be sending to the Transportation Management Center (TMC) where an algorithm is chosen there for optimizing the traffic flow in whole of the system.
Generally there

are

two

types of coordinated

ramp

metering

systems:

coordinated fixed-time control and coordinated traffic -responsive control
4-2-1- Coordinated Fixed-Time Control : This system doesn’ t use real-time analysis, as like as local ramp metering systems, it uses constant historical demand. The advantage of this type is its simplicity and its methodical style for calculating the best solution for each condition.
4-2-2- Coordinated Traffic-Responsive Control : This type uses a real-time analysis with very complex formulas which optimizes the total traffic flows in ramps. 12

5- Design of Metered Ramps
The geometry design of ramps (including the design of ramp meters) should be normally base on projected peak hour traffic volume for 20 years after the construction as cited in Highway Design Manual (HDM) Index 103.2. The annual
Traffic Volume book is not adequate for the reason of designing ramps and the designers require using the current data for this reason. The design of ramps is discussed for different types of entrances as can be read in flowing.
A. Metered Single-Lane Entrance Ramps:
The geometric design for single -lane entrance ramp should be design for up to 900 vehicles per hour. Figures 1 and 2 show the detailing design of this kind of ramps. This is noted that when the truck volume
(3-axles or more) is over 5% on the entrance of a freeway with sustained upgrade exceeding 3%, then a minimum of 150 meter length is needed to be provided beyond the ramp convergence point.
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B. Metered Multi -Lane Entrance Ramps:
When the traffic volume exceeds 900 vph then it is needed to provide an HOV lane or increasing the number of ramps to two or three. The detailed design for two -lane ramps is provided in Figures 3 to 5; and the detailed design for metered three -lane ramps i s provided in
Figures 6 and 7. For Three-lane metered ramp it’s needed to provide a tangential or least radius of 90 meters because these ramps needed to serve the peak hour traffic for urban and suburban freeways. So, for minimizing the revere effect of b us and truck traffics the geometric design is needed to have some specifications as discussed before.
The recommendation width for different metered ramps can be seen in following table:

C. Metered Freeway-to-Freeway Connectors:
These connectors need to pro vide a high warranty link between freeways. Because the drivers who driving in freeways, do not except to stop or reduce their speed in some special places of freeways. So the geometric design criteria for metered freeway-to-freeway should be as following:
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 Standard lane and shoulder widths
 "Tail light" sight distance, measured from 1070 mm eye height to a 600 mm object height, is provided for a design speed of 80 km/h minimum.
(See Figures 8 and 9)
D. Storage Length:
For maximizing the effect of strategies use d in ramp metering systems, an important factor is providing an adequate storage place for queues. The number of stored vehicles is depended on the special characteristics of each freeway. To minimize the impact of ramps on the local

street

operation,

the

designers

should

provide

the

recommended storage length of ramps . If according to geometric limitations the recommended length of ramps cannot be provided, then other alternatives can be used as widening the ramp meters or etc. E. Structural Section:
For considering the future development of ramps, the shoulder of ramps should be equal to their structural section (asphalt layer). In some special locations where there is concern of asphalt failure in loop detectors, a Portland Cement Concrete (PCC) pad may be considered. 15

F. Meter location:
On single-lane ramps the ramp meter signal should be positioned on the driver’s left. The detail of ramp metering signals for other two-lane or three-lane ramps can be seen in Figure 10.
G. Limit Line Location:
The minimum of li mit line location should be 23 m upstream of the 7 m point on the entrance ramp as shown in Figures 1 to 9. A single
300 mm solid white line should be considered across all metered ramp lanes.
H. HOV Preferential Lane:
The association of ramp meter installations to other transportation management system also should be considered. For instance, ramp meter installations should include the professional treatment of carpools and

transit

riders,

etc.

One

of these

transportati on

management systems is High Occupancy Vehicles, called HOV. The access route to HOV needs some ramps that its design geometry specifications can be found in Figures 17 and 18 of Ramp Meter
Design Manual for Department of California Highway Patrol.

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6- Conclusion
In this paper, first a definition and introduction to ramp metering will be defined and discussed in detail. Then the ramp metering concept will be discussed in three main subjects, Ramp Metering Algorithms, Types of Ramp
Metering and Design of Metered Ramps. A briefly discussion about the mentioned three subjects were done, but the main paper will cover these topics in more details. Also a Cost Analysis will be investigated in the main paper between the different methods of using ramp metering systems and it will be presented in the Presentation session.

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7- References:
[1] “Evaluation of Coordinated and Local Ramp Metering Algorithms using Microscopic Traffic Simulation” [Online], by Joseph R. Scariza,
Master of Science in Transportation at the MASSACHUSETTS
INSTITUTE OF TECHNOLOGY June 2003, © 2003 Massachusetts
Institute of Technology. All rights reserved.
[2] “Evaluation of Ramp Control Algorithms Using A Microscopic Traffic
Simulation

Laboratory,

MASTER

OF

MITSIM”

SCIENCE

[Online],

IN

by

Masroor

TRANSPORTATION

Hasan, at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 1999,
©1999 Massachusetts Institute of Technology. All rights reserved.
[3] “Optimization

and

Micro

simulation

of

On-ramp

Metering

for

Congested Freeways” [Online], by: Gabriel C. Go mes, University of
California, Berkeley, California PATH Research Report, UCB -ITSPRR-2004-44, November 2004, ISSN 1055 -1425.
[4] “RAMP

METERING

ALGORITHMS

AND

APPROACHES

FOR

TEXAS” [Online], by Nadeem A. Chaudhary, P.E. Research Engineer
Texas Transportation Institute and etc, September 2004, TEXAS
TRANSPORTATION INSTITUTE, The Texas A&M University System,
College Station, Texas 77843 -3135.
[5] “RAMP METER DESIGN MANUAL” [Online], Prepared by: Traffic
Operations Program In Cooperation with: Design and Local Prog rams
And Department of California Highway Patrol, January 2000.
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[6] “Adaptive ramp metering” [Online], Development of an adaptive capacity-demand ramp metering method, Marc Stanescu, May 2008 ,
Published by: ITS Edulab.
[7] “A New Ramp Metering Control Algorithm for Optimizing Freeway
Travel Times” [Online], By: Darren Lierkamp, This thesis is submitted in fulfillment of the requirements for the degree of Masters of
Information Technology The School of Information Technology and mathematical Sciences, The Univers ity of Ballarat, Ballarat, Victoria
3353, Australia.
[8] “HANDBOOK OF RAMP METERING” [Online], EURAMP, IST-200223110, European RAmp Metering Project, Contract NO 5076645,
Project Coordinator: IBI Group UK Ltd (IBI).
[9] “Integrated Ramp Metering Design and Evaluation Platform with
Paramics” [Online], by: Lianyu Chu, Will Recker, Guizhen Yu,
California PATH Research Report, UNIVERSITY OF CALIFORNIA,
BERKELEY ,UCB-ITS-PRR-2009-10, January 2009, ISSN 1055 1425.
[10] “Freeway congestion, ramp metering, and tolls” [Online], by: Pravin
Varaiya,

Department

of

Electrical

Engineering

and

Computer

Sciences, University of California, Berkeley, CA 94720 USA, July 25,
2007.

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