naeem rezghi ramp metering

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Ramp Metering

Term Paper

Progress Report

Name: Naeem Rezghi

Student ID: 8722229076

Course: Traffic Engineering, CIV4116-S12

Instructor: Mr. Peyman Misaghi

Date: July 1, 2012


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Table of Contents

1- Introduction ..................................................................................................................... 3

2- History.............................................................................................................................. 4

3- Ramp Metering Algori thms .......................................................................................... 5

3-1- System Architecture .............................................................................................. 5

3-2- Release Algorithm.................................................................................................. 6

3-3- A rbitration Algorithm .............................................................................................. 7

3-4- Switch On-Off Algorithm ....................................................................................... 8

3-5- Queue Override Algorithm.................................................................................... 9

3-6- Queue 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 platoonof

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 nave 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 some 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:

Manual On: When upstream line speed is low enough.

Manual 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:

Main 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 metering 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 needed 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 plan. 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 best

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 doesnt 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.


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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 is provided in

Figures 6 and 7. For Three-lane metered ramp its 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 bus 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 provide 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 used 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.


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F. Meter location:

On single-lane ramps the ramp meter signal should be positioned on

the drivers 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 limit 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 transportation

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, MITSIM [Online], by Masroor Hasan,

MASTER OF SCIENCE IN TRANSPORTATION 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. Gomes, University of

California, Berkeley, California PATH Research Report, UCB-ITS-

PRR-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 Programs

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 University of Ballarat, Ballarat, Victoria

3353, Australia.

[8] HANDBOOK OF RAMP METERING [Online], EURAMP, IST-2002-

23110, 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.

naeem rezghi ramp metering

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