TRAFFIC RESPONSIVE SIGNAL COORDINATION TRB TRAFFIC SIGNAL SYSTEMS COMMITTEE MIDYEAR MEETING JULY 25-27, 2003 – TORONTO, ONTARIO DENNIS EYLER VICE PRESIDENT SRF CONSULTING GROUP, INC. MINNEAPOLIS, MN
Purpose of Presentation Provide an overview of the capabilities of traffic responsive master controllers operating full traffic actuated intersections Present a few of the differences between adaptive and traffic responsive Suggestions for setting up a traffic responsive system TO GET THE OWNERS OF TRAFFIC RESPONSIVE MASTERS TO USE THEM!
Definition of a traffic signal A traffic signal is a device that allows traffic engineers to leave their intelligence at an intersection to operate it in their absence.
My perspective I have designed and operated over 40 traffic responsive arterial coordination systems consisting of full traffic actuated intersections. Most were on suburban arterial roadways with speeds in the 50 to 60 mph range
Arterial coordination systems in the Minneapolis suburbs 50 +MPH 40- 45 MPH Under 40 MPH
Audience poll How many people here are operating or have operated traffic responsive systems? Are these systems also operating with full traffic actuated intersection controllers? How many are on roadways with speeds above 50 miles per hour? Anyone used this type of system in an urban grid? How many people here are currently running an adaptive control system?
Why the poll? I am always willing to stand trial before a jury of my peers. However, I do want to make sure that I am in the presence of one.
Definitions - Traffic responsive master controller also known as “closed loop” • Has a library of prepared system timing plans – most systems are capable of 100 + plans • Variables • Cycle length, Offset, Splits, Grouping • Plan selection basedon • Volume levels, Directional distribution, Speed, Other inputs • Full traffic actuated controller – • Vehicular and pedestrian phases are enabled by detection. Vehicular phases are also extended by detection.
Definitions • Coordination • Merely a series of force offs and holds applied in an organized (presumably logical) manner to provide optimal flow through a group of traffic signals • Optimal • Like beauty, it is defined by the “eye of the beholder”
History of the traffic responsive & adaptive systems(at least that part that I can remember) • Early 1950’s – the 1022 controller with platoon carryover effect • Actually primitive adaptive control • 1960’s – electro-mechanical technology • Pre-timed controllers used as coordinators • Mn/DOT uses mutual coord device for 2 to 4 intersection systems, which creates a virtual single controller • Late 1960’s - First solid state master controllers • Mn/DOT insists on full actuated operation & uses leased phone lines for some two-way communication • Early 1970’s • Mn/DOT master controller cabinets are full ATR’s with data recording systems • Digital master controllers with digital coordinators • Late 1970’s – microprocessors and development of improved timing software • Microprocessor master controllers and microprocessor coordinators • Type 170 controllers
History (continued) • Early 1980’s • Second generation microprocessor controllers with internal coordination and precise time clocks also allows wider use of time based coordination • All temperature modems allow dial-up systems and give us the “closed loop” system as we know it today • Use of personal computers and Type 170’s as master controllers • Mid 1980’s • Use of arterial masters in urban networks • Duluth • Peoria • Others
History (continued) • 1980’s and beyond - Adaptive control systems are developed and deployed • SCOOT, SCATS, UTOPIA • TRAC • RT Tracks (OPAC, Rhodes and others) • City of Los Angeles • After 1980 - for traffic responsive systems • Development of area wide supervisory systems • Increased system capabilities
Arterial Signal Control Theory High Isolated – full actuated Responsive or adaptive Justification for “adaptable” operation Rigid coordination Low 1 2 3 4 5 6 7 Intersections per minute of travel time
Signal Control Theory High Signal control is adapted to traffic conditions Justification for “adaptable” operation Traffic is adapted to signal control Low 1 2 3 4 5 6 7 Intersections per minute of travel time
Responsive and Adaptive Objectives • Adaptive control systems • Minimize stop delay by optimizing splits and reducing cycle lengths • Stops are minimized through offset “optimization” • Traffic Responsive systems • Stop delay is reduced by cycle length selection and split control • Stops (particularly high-speed) are minimized by strict offset control and cycle length control • Oversimplifications • Adaptive minimizes stop delay, responsive minimizes stops • Adaptive works best in an open network of “equal” roadways, responsive works best on a high speed arterial or in a grid of regularly spaced intersections
Responsive and Adaptive Adjustments CYCLE LENGTH CYCLES
Understanding delay(not handled adequately by the HCM) • Delay is the time to traverse an area that is addition to the time it would take at the normal travel speed • Delay consists of: • Added path length (example: a loop ramp has a longer travel path than a directional ramp) • Geometric delay – traffic must slow because of intersection geometry (example: a roundabout) • Control delay – this has two components • The initial imposition of the control (example: a stop sign) • Delay because of a division of intersection capacity • Congestion delay – travel time added because of the interaction of the vehicles in the traffic stream • Speed differentials – cars versus trucks • Different driver behavior
Understanding delay • Lost time for stopping • A car - 30 MPH to stop to 30 MPH loses 12 to 15 seconds over traveling at a consistent 30 MPH • A truck losses 30 to 35 seconds • For 55 MPH a car loses 25 to 30 seconds • A truck at 55 loses 60 to 80 seconds (as do any vehicles behind that truck) • If delay is $13 for cars & $21 for heavy commercial vehicles at 7%, then a 30 MPH stop is worth $0.058 • A 55 MPH stop is $0.121 • Vehicle stopping costs are $0.045 and $0.15 for cars and trucks at 30 MPH and $0.085 and $0.30 for cars and trucks at 55 MPH • Total cost of stop $0.11(30) and at $0.22 (55) • Idling delay is $0.22/min and fuel adds another $0.03 for a total of $0.25
Implications • At high speeds, reducing mainline stops by adding delay to the side street is typically justified. • Early versions of the HCM virtually ignored lost time due to stops and assigned it a value of 30% of other intersection delay. • At 55 MPH and with V/C ratios of .5 to .6 “snappy timing” can cause lost time due to stopping to be 2/3 of the total delay. For a high-speed approach near capacity, lost time for stopping would be still be over 40%.
Traffic responsive system capabilities • Master controller: • Uses a library of prepared system timing plans • Most systems are capable of 100 + plans • Variables • Cycle length • Offset • Splits – real time with actuated controllers • Grouping • Crossing artery synch • Plan selection based on • Volume levels & directional distribution • Speed • Time of day • Special detection & other inputs • Serves as a communication hub and allows remote intersection monitoring and timing plan changes
Adaptive system capabilities • Central controller: • Processes data and is home to the “algorithm” • Coordination is “real time” • Infinite plans • Communication hub with some monitoring • May have an emergency backup fixed plan • Variables • Splits • Cycle length • Offset • Grouping • Adjustments are based on prediction of arriving traffic: • Size of platoon • Turn percentages • Arrival time
Arterial time-space diagram ¼ mile spacing - 45 mph progression speed – 120 second cycle Lead – lag lefts Lead lefts Lag - lead lefts
Arterial time-space diagram 1/2 mile spacing - 50 mph progression speed – 75 second cycle
Stated objections to traffic responsive control • Labor to develop and maintain timing plans • Expertise required to setup system • Rigid cycle lengths • Slowness of response to changing conditions • Early releases causes coordination problems • Funding is available to install adaptive control, funding may not be available to hire staff for operating a traffic responsive system
Actuated mainline green in coordination Mainline extension Added mainline green from no call on following phases and force offs held in place Coordinated green Added front end green from unused phase time and force-offs moved forward
TR Systems Setup Issues • Understand what detection your master controller will have available to make its plan selection • Where is capacity an issue • Where is directionality of flow an issue • Detection to determine offset and cycle length may be at different locations
TR Systems Timing Issues • System timing plans should cover a range of representative conditions, not be a collection that is simply created from computer solutions that are based on data snapshots • Round off traffic data • Chart the day’s expected flows and fluctuations • Check the “natural” cycle lengths • Constrain software for best solutions within cycle length ranges
TR Systems Timing • Create plan library to handle the range of traffic conditions • Create timing plans for saturated conditions • Create timing plans for incidents • Determine the “free to coordinated” threshold (about 100 vehicles per lane per hour) • Test plans to see which conditions overwhelm and at which point they are sluggish • Outline a typical daily schedule of which plans are in use at which times • Look at how offset adjustments and cycle length changes will be made. Have major changes occur at the most congested intersection
The future of arterial systems • Modern adaptive control and traffic responsive control are not far apart • Eventually, several adaptive control algorithms will reside in a system and be available for use when needed. This is similar to what happens today with systems that switch between TOD & TR • Adaptive control algorithms will use normal detector locations or use alternate detection locations with video detection
Observations and lessons learned • Hardware and technology can only go so far, you still need quality people • Early release is considered a “problem” for a traffic responsive arterial system. For adaptive control it’s considered a “feature” • If you can understand it, it’s obsolete