Signal Optimization (Coordination) Program
One of the fundamental parts of the City’s Congestion Management Plan 2016 – 2020 is to maintain signal timing plans to ensure they are up-to-date and responsive to the needs of all road users. The aim of the City’s Signal Optimization Program is to undertake signal coordination studies on a five-year cycle for major arterial roads, and on a 10-year cycle for minor arterial roads. Within the five-year cycle, a one-time study may be required for a portion of the route if there are significant changes in traffic volumes or land use. Coordination studies are not undertaken for traffic adaptive systems, such as SCOOT.
The City uses Synchro® software to develop optimized signal timings plans. Studies are done in conformity with the City’s Guidelines for Using Synchro 9 (including SimTraffic 9).
"Signal Retiming" vs. "Signal Coordination" or "Signal Optimization"
Toronto’s Signal Optimization Program is a coordinated effort designed to make the most efficient use of Toronto’s 2,376 traffic signals (as of July 24, 2019) by improving traffic signals, gathering up-to-date traffic data, and taking advantage of new technologies. “Optimization” in this context refers to all maintenance, upgrades, timing adjustments, and miscellaneous efforts to improve our signals.
The basic goal of signal coordination is to take a group of fairly closely spaced vehicles (called a platoon) travelling in the same direction through a series of intersections at or near the speed limit.
How the City Retimes a Route
City staff start by gathering data for each intersection along the route to establish the most up-to-date travel patterns. Once the data is gathered, engineers use computer programs to develop the best timing scenarios for each intersection on both an individual intersection and a route basis. Generally, signal timing plans are developed and/or updated for six periods – morning peak, day off-peak, afternoon peak, evening off-peak, night, weekend. Traffic diversion plans are also developed for routes that run parallel to the City’s expressways e.g. Leslie Street or Victoria Park Avenue.
What a Driver Should Expect After a Corridor is Retimed
As the goal is to minimize overall delay throughout the road network, drivers can expect to be stopped less frequently with the busiest traffic movements being given precedence over the less busy traffic movements. For example, the Leslie Street signals were generally coordinated with preference to southbound traffic in the morning peak period, northbound traffic in the afternoon peak period, and both directions during all other periods.
Signals are grouped into zones that are called control areas that can change by time of day. Generally, the control areas in the morning and afternoon peak periods are bigger since our aim is to move platoons of traffic to reduce travel time, stops, vehicle delay and fuel consumption. In the off-peak period, we operate major/major intersections (such as Leslie Street and Sheppard Avenue) by themselves because of their operating characteristics. Drivers may encounter delays when the control areas change.
Signals on the City’s major arterials are coordinated all the time. Signals on the City’s minor arterials and collectors are coordinated at all times except overnight generally between 10 p.m. and 6 a.m.. During the non-peak times, there are fewer cars on the minor arterials and collectors and therefore less benefit from coordination to the overall driving public. In addition, drivers are less willing to accept the side street delays.
Guidelines for the Design of Traffic Signal Coordination
- Signals spaced less than 1 km apart are to be coordinated during the peak periods.
- Signals spaced less than 0.8 km apart are to be coordinated during the off-peak periods.
- Where the percentage of traffic flow is greater than 55 per cent in one direction, one way progression in that direction is to be provided; otherwise two way progression is to be provided. When favouring one direction, emphasis should be on coordinating relative to the start of green intervals.
- If a capacity problem exists in the heavier volume direction, then the lower volume direction should be favoured for the section of route and/or period during which the capacity issue occurs.
- For signals spaced 100 to 150 m apart, the amber intervals should be synchronized under system control during all times of the day.
- For signals spaced less than 100 m apart, implement physical hardwire interconnect and simultaneous amber indications, or limited vision signal heads.
- The posted speed should be used to establish signal coordination plans.
Benefits of a Properly Coordinated System
- Less frequent stops in the coordinated direction of travel.
- Better speed harmonization which can increase safety and reduce rear-end collisions.
- Reduces the impact of automobile travel on energy consumption and air quality.
Measures of Effectiveness (MOEs) are measurable parameters that demonstrate the benefits, impacts, and cost-effectiveness of signal timing plan alternatives for the individual intersection, associated route and entire network. The City uses these parameters to evaluate the effectiveness of signal coordination studies. The following MOEs are reported: vehicle delay (hr), stops (#), average speed (km/h), fuel consumed (L) and greenhouse gas emissions (kg). In addition, an overall benefit-cost analysis is developed for each individual corridor.
The 2012 – 2016 studies have resulted in reductions in overall vehicle delay, travel time, vehicle emissions, stops and fuel consumption on the routes that were optimized; there was a slight increase in vehicle speed on these routes.
Based on the United States Environmental Protection Agency’s Greenhouse Gas Equivalencies Calculator, the reduction of fuel consumption achieved by the 2012-2016 studies is equivalent to the reduction of carbon dioxide emissions from 6,458 homes’ electricity use for one year or carbon sequestered by 41,395 acres of forest in one year.
The benefit/cost ratios from 2012 to 2016 were between 33:1 and 75:1 with a total cumulative saving over the three-year life cycle period of $271.1 million across all routes. The total life cycle benefit/cost ratio is estimated at 53:1. This means that for every dollar invested by the City, there was a potential saving of $53.00 to the public.
Limitations of Signal Coordination
Signal coordination is subjected to a number of constraints which limit the City’s ability to provide perfect coordination over long stretches of roadway. Such limitations include changes in roadway environment, midblock traffic disruptions (e.g. driveways, on-street parking, pedestrian crossovers), and the competing roadway demands of pedestrians, bicyclists, transit vehicles, and cross-street traffic. It is also inherently much more challenging to provide perfect coordination on two-way corridors compared to one-way streets. Hence, while we are able to provide nearly perfect coordination along routes such as Adelaide Street and Richmond Street where we are coordinating in one direction only, we cannot achieve the same performance level along routes such as Leslie Street since we must accommodate for two directions of travel.