Junction Design with Traffic Signals Wednesday March 2 nd 2016
Overview Introduction Context Conventional Approach Sustainable Approach Analysis Design Summary
Introduction
What are Traffic Signals? Purpose To separate conflicting traffic by the division of time and space in a safe, efficient and equitable manner How? The art of designing an installation is in reducing the delay and increasing the capacity while still maintaining a high degree of safety.
A little bit of History Houses of Parliament 1868 Manual Gas Picadilly Circus 1926 Dublin: August 1938 Merrion Square / Clare Street
Context
Purpose Why Where Analysis Design How
Why? Sustainable Approach Pedestrian & Cyclist Priority Conventional Approach DMURS Vehicle Priority DMRB
Where? Urban Areas: Design Speed / Speed Limit 60KMH OR LESS
How?
Conventional Approach
Why Conventional Approach Maximise Vehicular Traffic Capacity
Conventional Approach: DMRB Minimise Vehicle Delay and Optimise Vehicle Capacity Lowest number of conflicting phases and practicable stages in any signal cycle; Each vehicular approach is capable of carrying the maximum predicted flow for that approach; Allocating time to each phase/stage appropriate to the actual traffic flow Co-ordinating control of adjacent junctions to maintain traffic platoons.
Conventional Outcome
Sustainable Approach
Sustainable Approach DMURS Movement and Place
Sustainable Approach DMURS: Movement and Place Smarter Travel (2009) requires greater priority to be given to the movement of pedestrians in order to facilitate more sustainable travel patterns. Reprioritisation of traffic signal timings to favour pedestrians and cyclist Where pedestrian activity is high junctions may have to operate at saturation levels for short periods. Allow pedestrians to cross in single direct (short) movement. Diagonal Crossings may be applied. Buses should not be unduly delayed
Conventional Approach Sustainable Approach
Sustainable Approach: Choice of Junction Junction Options Shared Space Uncontrolled Priority (Stop or Yield) Roundabout Traffic Signals Removal of Traffic Signals?
Sustainable Approach DMURS: Junction Design Guidance Provide Crossings all arms Reduce kerb radii Omit left turn slips Omit Staggered Crossings Omit deceleration lanes pedestrian desire lines reduce crossing width / slow vehicles cyclist safety & minimise pedestrian delays minimise pedestrian delays not required < 60 kmh Pedestrian & Cyclist waiting times of less than 90 seconds
Sustainable Approach End of an Era??
Analysis
Definitions Cycle: A repetition of the sequence of signalling operations, during which each of the demanded traffic movements are served in turn Stage: Period of the cycle which gives right of way to one or more particular phases. Phase: The signal sequence for streams of traffic that receive identical signal display Intergreen: The period between the end of the green display for one stage and the start of the green display for the next stage Early Cut Off: To facilitate a heavy right turn movement from one approach, the green time of the conflicting opposing stream can be terminated earlier. Early Start: Alternative to an early cut off, an early start displays an indicative arrow whilst delaying the start of the opposing traffic.
Typical Layout A B D C
Staging and Phasing: Four Arm Junction
Manual Preliminary Assessment First Principles (TAL 1/06 TA 16/07) y = Ratio of demand to saturation flow y1 = Highest y value in a stage Y = y1 + y2 + y3 for three stage cycle Ymax = 1 (L/C) L = Lost Time Intergreen = 5 secs each Full Pedestrian Stage = 15 secs C = Cycle Time Optimal = 90secs Max = 120 secs Ypract = 0.9Ymax Cpract = 0.9L / (0.9 Y)
Manual Preliminary Assessment Y= 0.71 No Pedestrian Stage L = 15 C = 90 Ymax= 0.83 Ypract = 0.75 Full Pedestrian Stage L = 30 C =90 Ymax= 0.66 Ypract = 0.59 Cpract = 140 + Mitigate Delay: Combine Stages 1 & 2/ Early Cut Off Arm A
Manual Preliminary Assessment Y= 0.6 No Pedestrian Stage L = 15 C = 90 Ymax= 0.83 Ypract = 0.75 Full Pedestrian Stage L = 30 C = 90 Ymax= 0.66 Ypract = 0.59 Cpract = 90
Stages and Phasing: Right Turners
Stages and Phasing: Right Turners Early Cut Off Early Start
Design
Design DMURS (ish)
Design TD 50/04 Inter-visibility Lane Widths Right Turn Lanes Left Turn Lanes / Filters Swept Paths Lighting Location of Signals Pedestrians Cyclists Equestrian Signalised Roundabouts
Pedestrians General Issues: Keep Delays to a minimum Crossing Width: 2.4m minimum Crossing Type: Dished or Raised Stage Options: Full Pedestrian Stage (All Red) Walk with Traffic Staggered
Traffic Signal Control Types Fixed Time : Inefficient / Dependent on historical data Vehicle Actuation: Efficient/ Responds to ongoing traffic conditions Detection / Stage Called Minimum Green Time Maximum Green Time / Next Stage Called Detection / Extension of Green Time Control Systems Junction: Isolated Adaptive Control MOVA (Microprocessor Optimised Vehicle Actuation) TD 35/06 Low Flow: Delay Minimising / High Flow: Capacity Maximising) Network: Linked System / Urban Traffic Control (UTC) SCOOT (Split Cycle Offset Optimisation Technique) SCATS (Sydney Coordinated Adaptive Traffic System)
Summary
Context Conventional Approach Sustainable Approach Analysis & Design Where Why How