SCOOT : Basic Principles - Institute of Highway Engineers · 2nd Int. IEE Conference on Road ......

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www.theihe.org | Traffic Signal Control Course, Birmingham, 20th May 2015

SCOOT :

Basic Principles

Dave Carr

Source : Webster and Cobbe, 1966 &

TRRL Test Track, Crowthorne, Berkshire

1960’s – The Decade of Traffic Signal Research,

Experiments and Theoretical Modelling

Developments in traffic signal control systems

1960 1970 1980 1990 2000 2010

UTC started in mid 60’s

SCOOT development began in

early 70’s and first commercial

systems operational in 1984

(UK total 102)

Siemens 74 Imtech (Peek) 28

TfL

Fixed Time Plans Adaptive Plans

(SCOOT)

Time

Control

System

UTC/SCOOT

Source : TRL Transyt workshop exercise

Example of a Transyt Network

2

Transyt Output

Source : S.E.J. Consulting – Priory Way, Hessle

1970’s : Fixed Time UTC Systems -

Norwich UTC

0

5

Time (years)

0

10

15

20

25

1 2 3 4 5

SCOOT control

Fixed

time

plans

System effectiveness : the ‘ageing’ of Fixed Time Plans

% im

pro

ve

me

nt

ove

r

un

co

ord

ina

ted

co

ntr

ol

(Split Cycle and Offset Optimisation Technique)

Source : M.C. Bell & R.D. Bretherton,

2nd Int. IEE Conference on Road Traffic Control, London, 1986

Pa

yb

ack tim

e (

ye

ars

)

Number of signals in the controlled area

1

2

3

20 40 60 80 100 120 140 160

Payback Times for UTC/SCOOT Systems

UTC and SCOOT traffic control

systems are extremely cost effective.

Almost all systems repay their

capital costs within one year!

Source : UTC – The Kent Experience,

M.S. Bourner, Kent County Council, 1986

3

Source : DfT Traffic Advisory

Leaflet 7/99 : SCOOT UTC

The Flow of Information in a SCOOT

based Urban Traffic Control System

SCOOT/UTC

(traffic signals)

Fault

management

& reporting

CCTV

Text

Message

Signs

Remote

Monitoring

(dial up traffic

signals)

COMET

(strategic

control)

Remote

Office

Terminals

‘Intelligent’ Traffic Control

ASTRID

(data)

ANPR

(journey times)

Barnsley’s Intelligent Transport Systems

Car Park

(occupancy)

Signs

(Computer systems in the control room)

Local network that connect

all ITS computer systems

to data

transmission

System:

Copper;

Fibre optic;

Broadband;

Wireless.

The Barnsley Traffic Control Room The Sandwell (Birmingham) Traffic Control Room

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The Cardiff Traffic Control Room Area

(whole city?)

Regions

(parts of city)

Nodes

(individual

signals)

Stages Links

(approaches)

Detectors

SCOOT Equipment Hierarchy

R SW

R HR

R PW

R CA

R SP

N45111

N45121

N45211

N45221

N45311

N45131 A

N45131 B

N45131 C

N45131 D

N45131 A1

N45131 A2

N45131 B1

N45131 C1

N45131 D1

N45131 / 1

N45131 / 2

N45131 / 3

N45131 / 4

A The conventions on this page

are for a Siemens SCOOT

system. Imtech (Peek)

conventions are mostly

similar but with individual

differences eg ‘G’

rather than ‘N’ for nodes.

Link A has 2

SCOOT detectors

(eg has 2 approach lanes)

The Whole City – what’s called the ‘Area’

SCOOT

Region

‘CA’

(Castle St)

SCOOT

Region

‘SP’

(Spring Bank)

SCOOT

Region

‘HR’

(Hull Royal)

SCOOT

Region

‘PR’

(Princes Ave)

SCOOT

Region

‘MO’

(Mount Pleasant)

Within the ‘Area’ are SCOOT ‘Regions’

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Within the ‘Regions’ are Nodes, Links & Detectors

Node

N10261 Node

N10241

Detectors

C1:entry

C2:entry

X1:exit

A1:stop line

Detector

K1:normal

Detectors

D1:normal

D2:normal

Detector

Q1:entry

Detectors

M1:entry

M2:entry

X1:exit

N1:filter

B1:filter I1:filter

Link N10261M

L1:entry

Link N10261K

Link N10241D

Link N10241C

Lin

k N

10261Q

Lin

k N

10241A

Lin

k N

10261L

Link N10261N

Link N10241B Link N10261I

Region

HR

Flared link

stop line

Nodes N10261 & N10241 can also

be set up as a single ‘MULTI NODE’

for ‘absolute co- ordination’

SCOOT loop in the road surface

2 metres wide

Variable length:

2 lanes max,

best if 1 per lane

Can also be uni-directional

SCOOT Detectors

• 5 types : entry, normal, filter, stop line & exit;

• Best if a detector cover one lane but it is acceptable to

cover two lanes but no more;

• 99% are slot cut in road surface. Above Ground microwave

detectors that are suitable for SCOOT are now available;

• Entry is for the approach from an upstream un signalled

node;

• Normal is for the approach from an upstream signalled

node;

• Entry & normal detectors are typically 10 secs to 30 secs journey

time to stop line (100 to 300 metres). Minimum of 6 secs;

• Filter detectors are used when it is impossible to position an

upstream detector eg a very short approach. Filters are

located beyond the stop line (from 2 to 20 metres) & are

frequently used for early cut off or filter stages;

• Stop line detectors are used to reduce the number of detectors

by re-using an existing (VA) loop;

• Exit detectors are beneficial but not essential. They allow

traffic flow data to be stored in ASTRID.

SCOOT =

Split Cycle Offset

Optimisation Technique

ie there are 3 optimisers: Split (duration of the green times)

Cycle time (changes according to worst node saturation in a region)

Offset (from one signal site to the next)

‘SCOOT’ : what’s in the name ?

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Change to

stage 1

Change to

stage 2

The Split Optimiser calculates the duration of the green

time for the subsequent stage a few seconds before

the end of the current stage.

Time (seconds)

-4 0 +4

The Split Optimiser

Change to

stage 3

Actual green time for stage 1 Actual green time for stage 2 Actual green time for stage 3

-4 0 +4 -4 0 +4

-1 0 +1

Temporary change of

-4, 0 or +4 seconds

Permanent change of

-1, 0 or +1 seconds

-1 0 +1 -1 0 +1

Node

1

Node

2

One cycle for node 1

One cycle for node 2

Change to

stage 1

Change to

stage 2

Change to

stage 1

Change to

stage 2

Difference in offset between

node 1 and node 2

Dis

tan

ce

Time Arbitary zero for time

The Offset Optimiser

-4 0 +4

Permanent change of

-1, 0 or +1 seconds -1 0 +1

Temporary change of

-4, 0 or +4 seconds

The Cycle Time Optimiser

Usually runs every 5 minutes

for each region.

It can also run twice as fast

(every 2.5 minutes) if a trend of

rising or falling flows has been

established.

SCOOT C01

Event Driven Message

Summary of the Optimisers

Optimiser Frequency Change time (seconds)

Split

Offset

Cycle

Time

(cy)

Every stage

change

Once per

cycle

Every 5 or

2.5 minutes

-4, 0, +4 (temporary)

-1, 0, +1 (permanent)

-4, 0, +4 (temporary)

-1, 0, +1 (permanent)

-4, 0, +4 (for cy 32 to 64)

-8, 0, +8 (for cy 64 to 128)

-16, 0, +16 (for cy 128 to 240)

Split Cycle Offset Optimisation Technique = SCOOT

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SCOOT road network data:

similar format to ‘Transyt’

N10261 N10241

Q

L

I

D

K C

B

A

N

X

M X

Region HR

1. max & min stage lengths;

2. intergreens;

3. links in stages;

4. link types;

5. upstream & downstream links,

Node

N10261 Node

N10241

Detectors

C1:entry

C2:entry

X1:exit

A1:stop line

Detector

K1:normal

Detectors

D1:normal

D2:normal

X1:exit

N1:filter

I1:filter

Link N10261M

L1:entry

Link N10241C

Lin

k N

10261Q

Lin

k N

10241A

Lin

k N

10261L

Link N10261N

Link N10261I

Flared link

stop line

Data preparation for a SCOOT Region

Region

HR

Link N10241B

B1: filter

Detector

Q1:entry

Link N10241D

Link N10261K

Detectors

M1:entry

M2:entry

outstation X10260

ip address 192.168.172.1 outstation X10240

ip address 192.168.172.2

Entering the data into the SCOOT/UTC computer SCOOT Validation

Last queued vehicle

Queue clear

time in seconds

SCOOT

loops

Stop line

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‘Roving Terminal’ for SCOOT Validation Link Validation

1. Journey time;

2. Queue clear maximum queue;

3. Start lag;

4. End lag;

5. Saturation occupancy (STOC).

Validation Is the process of setting up SCOOT so that it accurately models what is

happening on street. Each link must be validated independently. The process will take

up to an hour for each link and the following parameters have to be checked and assessed:-

…is the time taken (in secs) by a free flowing vehicle to

travel from the detector to crossing the stop line.

… is the time (in secs) for the link to clear if it were completely full – ie for a

vehicle stopped over the detector to travel to and cross the stop line.

… is the time (in secs) from a SCOOT stage starting to

the first vehicle crossing the stop line.

… is the time (in secs) from a SCOOT stage finishing to

traffic ceasing to travel over the stop line.

… is the discharge rate for a SCOOT link from the stop line measured in Link Profile Units (LPUs)

It can be equated to the saturation flow which is normally measured in veh/hr. SCOOT uses STOC

to determine how quickly vehicles discharge when the link is green. Typical values of STOC are

between 8 and 12 LPUs/sec for 1 lane and between 12 and 16 LPUs/sec for 2 lanes.

Probably the most

Important validation

parameter is ‘STOC’

and is almost like

‘saturation flow’

Operator Terminal Screen Display Operator screen

window for a single node System

code

number

Actual stage green times

& inter-greens

SCOOT

‘plan’

data

SCOOT green time splits are stage based and NOT phase based as in controller configurations!

Screen data

updated

every

second

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Node Fine Tuning Display Region Fine Tuning Display

Low traffic flows:

signals should operate under local VA or

MOVA control eg 21:00 to 06:30 on Monday to Friday

High traffic flows:

signals should operate under SCOOT

control eg 06:30 to 21:00 on Monday to Friday

Times for implementing SCOOT control

Whole city traffic flows

An appropriate timetable entry

for enabling SCOOT control on a

(Siemens) system would be:-

06:30 SCOO RAS

21:00 XSCO RAS

Times for implementing SCOOT control

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Part of a UTC timetable

www.theihe.org | Traffic Signal Control Course, Birmingham, 20th May 2015

SCOOT :

Basic Principles

to Strategies

Dave Carr

1960 1970 1980 1990 2000 2010

UTC started in mid 60’s

SCOOT development began in

early 70’s and first commercial

systems operational in 1984

UTMC research programme

started in 1997 & so did Siemens

ITMC (Integrated Traffic Management Computer) product. COMET was

developed and started to appear

from 2000.

(UK total 102)

(UK total 78)

Fixed Time Plans Adaptive Plans

(SCOOT) Strategies within

UTMC databases

Time

Control

System

‘COMET’

UTC/SCOOT

Developments in traffic signal control systems

UTMC systems are

Made by Siemens,

Envitia, Cloud Amber, Mott McDonald & Amey

ASTRID* screen window

My

favourites

shown with an

* Automatic SCOOT Traffic Information Database

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Strategies for traffic signal control systems:

MOVA to and from SCOOT

M1 jcn 37

A628

Dodworth

Rd

A

B

C

R

D

S

J21111

traffic

signals

A6133

Broadway

J21111: A628 Dodworth Rd/A6133 Broadway, Barnsley.

Detailed analysis in 2009 confirmed the benefits of SCOOT with queue relocation

compared to MOVA. The purpose of the queue relocation was to reduce the delays on

the A628 Dodworth Rd (links B and D) and this has been achieved by allowing delays on

the other links to be increased. It should be noted that queue relocation is only

implemented when individual links have degrees of congestion that exceed

predetermined thresholds. At all other times, SCOOT and MOVA co-exist and equitable

delays are experienced by all links.



MOVA loop

SCOOT loop



M1 jcn 37

A628

Dodworth

Rd

A

B

C

R

D

S

J21111

traffic

signals

A6133

Broadway



SCOOT link N21111B

congestion threshold 10%

SCOOT link N21111D


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UTC system log filtered for relevant messages for Friday 29th to Monday 31st March 2014:

(note SCOOT wasn’t actioned on Sunday 30th)


VMS legends associated with Dodworth Rd

ASTRID graph showing the N21111 node congestion

& N21111B link congestion on 31st March 2014

SCOOT node N21111

congestion threshold

20%



N21111B link




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****** Start of system log for 31-MAR-14 ******

Mo 07:36:15 B002 B003 B012 RDR RTE : stgy7101 : queue on A628 Dodworth Rd to M1

Mo 07:41:38 B002 B003 B012 RDR RTE : stgy7102 : congestion on A628 Dodworth Rd to M1 Mo 08:10:02 B002 B003 B012 RDR RTE : stgy7101 : cleared

Mo 08:10:02 B002 B003 B012 RDR RTE : stgy7102 : cleared

Mo 08:11:12 B001 RDR : stgy7105 : extreme.cong on Dodworth Rd from M1 to N21111

Mo 08:16:13 B001 RDR : stgy7105 : extreme.cong cleared

Mo 08:35:14 B002 B012 B014 RDR RTE : stgy7107 : congestion on Pogmoor Rd at Dodworth Rd

Mo 08:50:12 B002 B012 B014 RDR RTE : stgy7107 : cleared Mo 09:00:35 B005 RDR : stgy7103 : queue on Broadway

Mo 09:05:35 B005 RDR : stgy7103 : cleared

Mo 15:38:00 B002 B003 B012 RDR RTE : stgy7102 : congestion on A628 Dodworth Rd to M1



Mo 15:46:39 B002 B003 B012 RDR RTE : stgy7102 : cleared Mo 15:51:40 B002 B003 B012 RDR RTE : stgy7101 : queue on A628 Dodworth Rd to M1

Mo 15:56:22 B001 RDR : stgy7105 : extreme.cong on Dodworth Rd from M1 to N21111


Mo 16:00:18 B002 B003 B012 RDR RTE : stgy7102 : congestion on A628 Dodworth Rd to M1


Mo 16:25:11 B001 RDR : stgy7105 : extreme.cong cleared Mo 16:28:34 B002 B003 B012 RDR RTE : stgy7102 : cleared


Mo 16:40:14 B002 B012 B014 RDR RTE : stgy7107 : congestion on Pogmoor Rd at Dodworth Rd



Mo 17:30:22 B002 B003 B012 RDR RTE : stgy7102 : congestion on A628 Dodworth Rd to M1 Mo 17:46:58 B002 B003 B012 RDR RTE : stgy7102 : cleared


****** End of system log for 31-MAR-14 ******

VMS sign

number (s)

SCOOT

region

VMS

legend

UTC system log filtered for relevant messages for Monday 31st March 2014


VMS legends working automatically on

Shambles St (sign B002)

Free text VMS to show real time queuing & congestion

COMET overview window showing VMS legends Fri 11th April 2014 at 17:20



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SCOOT : Basic Principles - Institute of Highway Engineers · 2nd Int. IEE Conference on Road ......

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