Strategic Consideration on General Design of Chinese Freeway MC System

Copyright © IFAC Transportation Systems, Tianjrn, PRC, 1994

STRATEGIC CONSIDERATION ON GENERAL DESIGN OF CHINESE FREEWAY MC SYSTEM FENGXIANG QIAO' and JUNLI LI' , Southeast University. Department

0/ Communication &- Tra1lSportation

Engineering. Nalljing,

PRC

Abstract . Chinese freeway's monitoring and control systems (MC Systems) are not perpect now, which causes the phenomenon of "monitoring not control". This paper provides a strategic consideration on the general design of chinese freeway's MC system, including its design goals , principles , its system compositions and functions,its control strategies during different stages and it s hardware arrangement principles . Key Words . Transportation; road traffic; tra ffic control; control applications; monitoring

1. INTRODUCTION

functions, the divison of controlling strate-

Chinese economy has experiented a great

gies, the arrangemen of hardware and etc . of the general design of Chinese freeway's moni -

development since it pursures the "Reform

toring and control system.

and Open" policy. The length of freeways already built in China has reached about 2000 kilometers, although the first freeway ap-

2. GOALS AND PRINCIPLES

peared in Chinese main -land only in the early 1980's.

2. 1. System Goals

But the construction of Chinese freeways is still in its primary stage. Their monitoring

The design of freeway's monitoring and control system CMC System) must be helpful to

and control systems (MC systems) are not

the raising of freeway's capacity and the level

perfect, the reason of which may be that the

of survice, to the rapidly discovering of all

lengthes of some early freeways are short Ce.

kinds of unusual phenomena, to the effective-

g.

song freeway in

ly dredging of congestion, and to the properly

Shanghai is only 20. 8 kilometers), traffic

guiding and controlling of traffic, so that traffic can flow on best conditions, and

the length of xing -

flows are not heavy, financial supports are not enough, and etc. But the most important

freeway's rapidity, safety and comfort func-

reason is that the understanding and explain-

tions can be realized.

ning of monitoring and control system

IS

nar-

rowed to only" monitoring", and that a clear

The system goals which must be determined

guiding ideology and a ul1l10rm standard are

in general design are: the maximum traffic

lack, which causes the phenomenon of "moni-

operational safety; the least delay, 1 he least

toring not control" in many freeway systems

fuel comsume, the least number of stops and

in China.

the maximum transportation benefit; the best survice Coffering enough imformations about

This paper gIves a discussion to the goals,

roads, traffic, meteorology ~ environment and

the principles, the system composition and

etc., reducing drivers' psychological tense

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the general pl .. n of the whole freeway and implemented by stages.

ness and physical tiredness); the maximum helps to drivers when difficulty appea rs; and the maximum reliability for system itself.

3. COMPOSITION AND MOULDS 3. 1. Constructional Composition

2. 2. Design Principles According to the above five goals, there are

A main -control-centre is usually necessary

five design principles:

to give general orders, and some sub-control - centres can be set to generate concrete detecting orders, monitoring and control instructions. For example, in the Jiangsu part of Shanghai - Nanjing freeway, whose length

Ensuring against risks and increasing effectiveness. Safety and effectiveness are two aspects which must be overall balanced and considered as a whole during the design processes. When vehicles run in usual conditions,

is about 90 % of the total one, a general control centre is to be constructed in Maqun, located in the outer ring road of Nanjing, and governs five sub - control - centres (named

our main task is to fully utilize carriageways' capacities and ensure the best running states to achieve maximum effectiveness; when unusual phenomena appears, especially when accidents occur, the system must have the a-

Suzhou, Wuxi, Changzhou, Zhenjiang and Nanjing sub-centre).

bility to dredge congestion and give aids to drivers.

Main -control-centre. The location of main - control - centre should be helpful to the connection of main-centre and sub-centres, and to the future expansion. The constructional composition of main - control - centre

Using advanced tecnniques under our national situations. We can use all the advanced detecting, controlling, guiding and etc. techniques and all the advanced equipments. But all must be done on the basis of our national and provinces' situations.

Control board

Sub-centre delivery

Coordinating software, hardware and faults

Reserve computer

automatic diagnosis together. Requirements of hardware equipments can be reduced to the least if .software is excellently designed. And faults automatic diagnosis is the basis for

Driver imformation system

both hardware and software to work well. All these must be coordinated together.

System expending interface

I

t

~Centre

_

computer

Traffic data displayer Abnormal pbenomena displayer Accident displayer

Considering multiple relations comprehensivFig. 1. Constructional composition of main

ely. Relations between software moulds, be-

-centre

tween MC system and freeway's other traffic engineering systems, between main - centre and sub - centres, and etc. must be consid-

may be illustrated in Fig. 1.

ered comprehensively.

Freeway's main - control - centre may pro-

Designing generally and

vide the following functions: forming general centrol strategies to goven sub - centres and

implementing

by

3L urgent affairs;

stages. In different freeway mileages, differ-

dealing with some important

ent control tactics, different constructional

coordinating functions between freeway mainline and those substitute roads and between

drawings, different managements and etc. are permitted, which must be designed under

subcentres; collecting imformations on the

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system

goal~ .

whole comlOg from sub - centres; utilizing transportation radio to offer informations of traffic conditions, enviroments, road conditions and etc. to drivers; and receiving in-

Monitoring display moulds. Under the management of this mould, the substituting of

structions coming from higher control centres and shareing important informations with

display imformation, the changing of monitoring view, the fixing or printing or reserv-

them.

ing or dilivering of key image,and etc. can be realized.

Sub-control-centre. Fig. 2. shows the constructional composition of sub - centres, the

Operation Mould.

functions of which may be: accepting and executing main - centre's instructions and form

By man -

machine dia-

logue, one can input imformations, parameters, guiding and control orders directly on the control board. And the operational states for every functional moulds and the middle / terminal results can be checked.

their own strategies after considering traffic, road & etc. factors; pre - processing detecting informations and delivering chief one to main - centre timely; in charge of road maintaming and management; 10 charge of acciden t 's detecting, helping , recording, and

Driver

Information

System

Management

Mouds. To guide and control traffic, it is necessary to manage all kinds of dri ver imformation systems, so that traffic can flow con-

predicting affairs in the corresponding area, using advanced manners such as electronic detecting, urgent phone, chosed TV, patrol vehicle, driver's helping system, computer,

tinuously.

electronic display and etc.; monitoring and displaying traffic parameters such as velocity, occupancy, flow, delay, stop, oil comsump-

Traffic data analysing and reservlOg mould. By analysing and reserving traffic da ta, regularities of traffic flow and unusual traffic features can be found to predict future traffic sit-

tion and etc. either in the equipments in sub -centres or on the outer information boards and inner - vehicle displayers; and detecting

uations, to make road reconstruction plans, and to improve recent and future control strategies.

andrectifying faults automatically.

Accident analysing and reserving mould. Ex3. 2. Functional Moulds

pert system can be used to analyse the reason and the regularity of accidents. Chinese free-

By dividing according to software functions,

way traffic accident analysis software must be

12 moulds may be existed in freeway's mOI11toring and control system.

developed in a standard form, considering both science and experiments.

Information collecting and pre - processing

Road maintaining and management mould.

mould . Suitable sampling frequency, data pre

By using expert system, freeway's road and

- processor (if necessary) mus t be designed

traffic facilities can be maintained and man-

carefully.

aged

Some informations can be input

directly from control board (e. g. some road maintaining, accident, meteorological infor-

automatically

and

scientifically,

10-

c1uding statistics, analysis, prediction, eval uation, decision making and etc.

mations) System self - detecting mould. Traffic unusuMain control strategy mould. According to

al phenomenon analysis software, system's

kinds of imformations coming from freeway's

hardware & software fault diagnosis software

mainline, ramps and substitute roads, the

must

best

moulds and the entire system.

control

strategies

which

vary

from

stages, can be formed to meet the needs of

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be developed

to serve every other

4. STRA TEG Y STAGES Traffic volumes will continuously increased

Acciden t alarm

after freeways' building. The recently built freeways in China are normally located in the advenced areas and link two or more large

System fault display Map board Changeable information board

Traffic data display Meteorological detector

Control instruction display

central cities, whose lengthes are all about 300 kilometers and whose volumes are larger

Changeable

than early freeways'. So, we can make different control strategies during different stages.

velocity

Traffic detector Road guality

board T

Toll gate &. ramp controller

detector

I

Main control

4. 1. Foundation of the divition of strategy

centre

Contre computer

stages.

I Control board Printing terminal

The divition of strategic stages is the result of the contradiction between the continuousl y increase of traffic vol umes and the fixed

Toll gate, ramp control

-

Driver information system

freeways' capacities. The foundation of the divition of strategic stages must be traffic vol-

Inquiring terminal

T Camera Urgent phone fPatrol vehide

Closed TV Urgent phone monitor

Road main tainning dept.

ume and the level of service, not simply th e time periods.

Traffic management dept. Service llrea

4. 2. Strategy during the first stage.

Rescue dept.

Normally, during the primary period, traffic F ig. 2. Constructional composition of subcentre

volumes are far lower than capacities and the levels of service are A or B. Simple control

System evaluation mould. Efficiency evaluation system of freeway's MC system may be

control and (if necessary) ramp control. Ramp control may be used less than mainline

established by choosing suitable efficiency parameters, their weights and ecnomy convert-

control because during this stage, it is impor-

strategies may be adapted, such as mainline

tant to attract more vehicles onto freeways .

ing values to keep system's optimal operaton.

The factors which must be considered now are the safety of merging and weaving, the

Automatic traffic management mould. Illegal

well distribrution of traffic flow, the well

traffic actions will be detected, recorded and penalized automatically to the full by the application of this mould and of corresponding devices.

forestalling of accidents, and etc.

transportation broadcasting, carriageway closen, changeable information board con-

System software management mould.

trol, and etc. Most functions will be realized in sub-centres.

Control

manners include changeable velocity control,

All

above software moulds must be managed under a uniform system management software so that computers' capacities and data infor-

4. 3. Strategy during the second stage.

mations can be used to the extence and all moulds can get their best uses.

By the increasing of traffic volumes, the lev770

els of service will drop to a certain degrees (say, C or D) and the transportation efficiency will certainly be reduced. The proper strategies may be the integrated ramp control

are four principles for hardware arrangement: meeting the needs of information collection and being convenient for communication and data processing; acting the orders of monitor-

and mainline control. Traffic conditions all over the ramps and the main line must be considered and the metering manners and the metering rates for every ramps must be determind under a uniform strategy, the aim of which is to provide all vehicles entering the freeway best system running. Mainline metering is still important during this stage for

ing, guiding and control; arranging simply and being convenient for repairing and extending; being used in groups if possible. And four aspects must be taken into consideration in hardware choosing: advanced functions; good gualities; ecnomical choosing (using national products as possible); and automatic faults diagnosing.

the keeping of a continuous and not congested flow, and for the coordinating to ramps' metering control. Here, control areas may be restricted to freeway itself and its ramps, or if necessary, including less important up s tream intersections of ramps. Most control orders will also be generated by sub - cen tres.

5. 2. Hardware arrangement. Many hardware arrangement concern with the destruction of road surface and the expansion of computers' capacities and communication channels. So before road constructions during the first and the second stage, one must consider the arrangements of hardware during the second and the third stage, that is, consider how many rooms should be left for later according to a detailed list of hardware's important arrangements and replacements, the exact dates of which during the second and the third stage must be choosen in freeway's important repairing periods as possible so as to reduce financial wastes.

4.4. Strategy during the third stage . Freeway is one of the roads in the regional comprehensive transportation network. When traffic volumes increase to a certain extance, it is not enough to research only on freeway itself and its ramps. It is necessary to consider the general transportation efficiency of freeway, ramps, interrelated and parallel highways, and even to consider the connections to all possible UTCS (Urban Transportation Control System). During this

6. REFERENCES

stage, with the closely cooperating of subcentres, UTCS information systems, higher

Bruce, N. J. , L. S. Buckels and B. E. Peterson. (1991). Network design program-

control centres and etc. , main -control cen-

ming of U. S.

tres have to play an important part in generat-

Journal of Transportation Engineering, Vol. 117, No. 4 , July/August, pp. 457 - 479.

ing system optimal strategies, making proper reconstruction plans to freeways and other concerned highways, and etc.

highway improvements, the

Linkenheld, J. S. , R. F. Benekohal and J. H. Garrett. (992). Knowledge-based system for design of signalized intersections. the Journal of Transportation Engineering, Vol. 118, No. 2, March/April, pp. 241-257.

5. HARDWARE ARRANGEMENT 5. 1. Requirements of hardware.

Yorgos J. S., 1. Z. Argiropoulos and P. Michalopoulcs. (1990). On -line traffic as-

Hardware, which is the basis of information

signment for optimal freeway corridor control. the Journal of Transportation Engineer-

!E.g, Vol. 116, No. 6, November/December,

collection, traffic guiding and control, assures the existance of the MC system. There

pp. 744 -755.

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