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.
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