SCOOT: Basic Principles

Transcription

1 SCOOT: Basic Principles Steve Holder Atkins Transportation Consultancy IHE Professional Certificate in Traffic Signal Control This presentation should assist you with the following competences; Competence 23 Design a Traffic Signal Scheme Competence 35 Calculate CLF, UTC & Scoot Plans Competence 36 Assist with operating UTC/Scoot Systems (inc. amending database / Scoot validation) Competence 38 Link Traffic Signals on Arterial Routes Traffic Signal Control Course, NAL Worcester, 1 st June 2016 The Golden Age of Motoring. The reality of modern car ownership on an antiquated road structure. 1

2 1950 s/1960 s the period of Traffic Signal Research, Experiments and Theoretical Modelling Source : Road Research Technical Paper No. 56 (1966) F.V. Webster & B.M.Cobbe TRANSYT TRAffic Network StudY Tool TRANSYT was developed from Peter Whitings Combination Method which centres on the simplicity of platoon structures. The TRANSYT program was developed in 1967 by Dennis Robertson using assembler language, and it was first tested later that year on the Cromwell Road in London. 2

3 TRANSYT PROGRAM Transyt Performance Index Network Data Network Layout Link Lengths Traffic Flows Saturation Flow Rates Vehicle Speeds Signal Stages Predicted Stops & Delays TRAFFIC MODEL SIGNAL OPTIMISER Best Signal Timings Example Transyt Network Transyt output 3

4 % improvement over uncoordinated control 07/06/2016 Transyt issues. Fixed time plans age due to various factors. Based on historic flow data Accuracy of flow data Variability in the real world General trends of traffic changes Source : M.C. Bell & R.D. Bretherton, 2 nd Int. IEE Conference on Road Traffic Control, London, 1986 Fixed time plans Time (years) Something more was needed. A system that could maintain the effectiveness of the new Transyt plans A system that could remove the inaccuracy of historic data A system that automatically update itself A system that could take into account second by second changes in traffic flow SCOOT Split Cycle Offset Optimisation Technique System that produces signal timings that are constantly updated Uses flow data that is automatically updated Can take into account variability in traffic volume and routing 4

5 % improvement over uncoordinated control Payback time (years) 07/06/ Payback Times for UTC/SCOOT Systems SCOOT Control (Split Cycle and Offset Optimisation Technique) 2 UTC and SCOOT traffic control systems are extremely cost effective. Almost all systems repay their capital costs within one year! 10 5 Fixed time plans Source : M.C. Bell & R.D. Bretherton, 2 nd Int. IEE Conference on Road Traffic Control, London, 1986 Time (years) Source : UTC The Kent Experience, M.S. Bourner, Kent County Council, 1986 Number of signals in the controlled area The Urban Traffic Control System Urban Traffic Control Centre's Source : DfT Traffic Advisory Leaflet 7/99 : SCOOT UTC Coventry Urban Traffic Control Centre Circa

6 Coventry - today Birmingham Coventry s Urban Traffic Control Centre Circa 2015 Scoot what s in a name? SCOOT = Split Cycle Offset Optimisation Technique There are 3 optimisers Split Cycle time Offset Principles of Scoot Scoot uses 3 key ideas to underpin its strategy; 1. Measures Cyclic Flow Profiles 2. Online Traffic Model 3. Incremental Optimisation 6

7 Example of Scoot Principles Cyclic Flow Profile The Split Optimiser The Offset Optimiser 7

8 The Cycle Time Optimiser Summary of the Optimisers Scoot Plans Scoot Hierarchy Timing plans are used by Scoot to control the signals Timing plans are used as a base for Scoot to proportion the cycle time Only certain cycle times can be used Stages Area (whole town/city) Regions (parts of city) Nodes (individual signals) Network (site data) Links (approaches) Detectors 8

9 Scoot Data Scoot region data can be thought of having two distinct elements; 1. Network data - the topographical definitions of the region. 2. Link data - defined in the network data; individual approaches within the region. The whole city - Area Scoot Regions Scoot Region Example = approximate area of Scoot region 9

10 Nodes, Links and Detectors Region Diagram = Node = Link Scoot Link Types There are 4 types on an Imtech system Entry links coming into a region Normal links between links Filter links normally after the stop line Exit links leaving a region Scoot Detectors Usually inductive loops (well over 95%) Other technologies available i.e. Magnetometers Overhead detectors (e.g. microwave) 10

11 Scoot Loop Siting - 1 Scoot Loop Siting - 2 Offside edge of detector approx. 1 metre from centre line At least 25 to 30m downstream of Pelican crossing markings At least 10 to 15m downstream of signalised junction Avoid placing loops where they are likely to get parked or queued on if possible. Try to place loops so traffic can achieve free flow speeds. Preferred detector locations Normal Links Entry Links Upstream end of the link m from the stop line 10 15m from the previous junction Beyond the expected 1m from the kerb edge maximum queue 1m from the centre line 2.5m between detectors on adjacent lanes Scoot Loop Siting - 3 Scoot (Inductive Loop) examples Recommended loop length = 2 metres (in direction of travel) One loop for 1 or 2 lanes Two loops for 3 or 4 lanes Three loops for 4 + lanes 11

12 Scoot Loop Actual example Scoot Loop Siting - summary Narrow loop due to lane width. Must not detect oncoming traffic. 2 metres deep Variable length: 2 lanes max per single loop 1 per lane = best practice Critical to deploy correctly Can adversely effect Scoot performance Please note that compromises sometimes have to be made, but take that into account in the data. Remember: Rubbish In = Rubbish Out! Scoot Loop Example Scoot Detector Pack 12

13 Network Data Example Link Data Example - 1 Link Data Example - 2 Data preparation for a Scoot Region Parameters critical to Scoot performance; Congestion Importance Factor (CGIF) Journey Time (JTIM) Maximum Queue Time (MAXQ) Saturation Occupancy (SATO) 13

14 Parameter Definitions Scoot Validation - 1 CGIF - how important is it to avoid congestion? (0=unimportant / 7= critical) JTIM Average time for a vehicle to travel from detector to stop line in free flow conditions MAXQ length of time a maximum queue takes to clear the stop line (i.e. a queue that is from the stop line to the detector loop itself) SATO* the maximum outflow rate that traffic can cross the stop line in link profile units per second; *Subject of Scoot Validation This is the process of fine tuning the saturation occupancy value to mirror actual traffic behavior on street. Uses an on street observer (with a stop watch) to time the period it takes a queue to clear the stop line on the relevant link and either a roving terminal or other access to a system terminal. Scoot Validation - 2 Operator Screen for Validation 14

15 Scoot Validation: Original Method Saturation Occupancy; Filter Links 1 Street Count of queue at start of green (vehicles) Measure queue clear time as time from start of green so that the last delayed vehicle crosses the stop line. Control Room Queue at start of green (LPU s) from the M10 message Convert to vehicles (approx. 17 LPU s per vehicle) Modelled queue clear time M11 message M75 & M77 (Scoot v4.5 or later) M14 for additional queue detail Compare street values with Scoot model over a number of cycles Adjust saturation occupancy such that the model matches on-street observations (+ check new value) Notoriously difficult to calculate Methodology; measure the usage (saturation) of the filter stage and compare to the Scoot model Downstream node; Scoot should be active (Scoot messages required) / Split optimisers should be in limbo mode (not optimizing) Initial value; start with a reasonable estimate of saturation occupancy / typically 6-9 LPU s per second for a single lane Saturation Occupancy Filter Links 2 Street Each cycle measure: Green length (g) Time taken for vehicles queuing at start of green to discharge (t) Number of other (non-queued) vehicles that also go through on green (n) Estimate saturation as: DoS = (t+2n)/g x 100(%) Control Room Degree of saturation from the M08 message Compare calculated street values with Scoot model over a number of cycles Adjust saturation occupancy such that model matches on-street observations (+ check new value) Values within 10 15% of each other is a sufficient match Roving Terminal 15

16 Extract from a UTC Timetable UTC Timetable explanation Other Facilities Scoot through the years Bus Priority in Scoot ASTRID (Automatic Scoot Traffic Database) INGRID (Integrated Incident Detection) Version 3.1 bus priority & incident detection Version 4.2 estimates of pollutants Version 4.5 bus priority enhancements Scoot MC3 packet switched comms, congestion supervisor & stage skipping Scoot MC3 (SP1) ped crossing improvements Scoot MMX ped priority & emissions estimates Scoot MMX (SP1) journey time reliability facility 16

17 Results from Scoot - Nationally Coventry London M25 Preston Southampton Worcester York Results from Scoot - Internationally Beijing Santiago Sao Paulo Toronto Further Reading. IF YOU THINK THINGS ARE BAD 17

18 And finally. Thank you for listening. Any questions? 18