Technical – Page 3

If you receive construction emails from us, you might know that we’ve installed vehicle detector loops at intersections with traffic signals. But if you’re like most people, traffic lights, and their various components [what are vehicle detector loops, anyway?] are probably one of those subjects you don’t give a lot of thought to. So next time you’re waiting for that light to change, here’s a primer on vehicle detector loops, and why you’ll be glad we’re installing them as part of our projects.

To begin with, vehicle detector loops [the technical term is “inductive-loop vehicle detectors”] are flat, loose coils of wire covered in light plastic, which are buried in the asphalt under the lanes at an intersection.

In York Region, most of our vehicle detector loops are approximately 4 metres square, and extend from the pedestrian crosswalk and across the stop bar [the wide white line going across each traffic lane at intersections] for approximately 15 metres.

The point of a vehicle detector loop is to detect when vehicles are sitting at the intersection. Vehicle detector loops are able to do this through a process of magnetic induction, which results when metal objects [i.e., vehicles] are nearby. Put simply, the presence of the vehicle results in a change in the magnetic field of the loop. This change is detected by the traffic signal controller [a large box located near every signaled intersection], which in turn sends a message to the traffic signal to begin turning from red to green.

York Region owns and or maintains 848 signalized intersections [traffic lights occasionally are used in other settings such as single lanes through construction zones]. Most of York Region’s traffic loops are located on side street lanes, in left turn lanes to activate advanced left turn signals, and on rapidways to detect transit vehicles.

The Region also uses “Matrix” vehicle detection, a pole-mounted system using radar imaging, in construction zones where lanes are moved, and where it’s problematic to install traffic loops. For more information on the technology of traffic signals, check out york.ca/intersections.

Ultimately, traffic loops improve the performance of an intersection, helping traffic flow by detecting you better.

When it comes to traffic lights, there is a clear favourite: no one likes red, but everyone loves green. And those advanced green arrows are great, except that they never seem to last long enough. Seriously, traffic signals are one of those aspects of commuting that we all have strong feelings about. But what determines when a light changes from red to green, and how long that advanced green should last? Let’s try to shed some light on that…

There’s nothing random about the timing of traffic signal phases, and their design has only one goal: to move traffic and pedestrians as freely and safely as possible along our roadways. As with all aspects of civil and urban design, things are more complicated than they might seem, requiring clear priorities and tradeoffs to balance out everyone’s needs. Here are the basics.

In traffic engineering-speak, a signal phase refers to the operation for all approaches to an intersection [e.g., a red light will show for a side street at the same time as the main road has a green light]. A cycle is the entire combination of phases for an intersection [red, green, amber, advanced green etc.]. A cycle can range from 90 to 160 seconds [meaning if you miss a green light, that’s how long you could wait until the next one], although the timing depends on the intersection and the time of day.

Determining what phases are needed for the cycle, and how long each phase will last, reflects the needs of all users – including transit, pedestrians, cyclists and drivers. Some phases in the cycle length ensure that road users are not in conflict with one another [for example, drivers can’t exit a side street at the same time as drivers are going straight through on the main road]. Also, some users’ needs will be parallel within a phase – e.g., pedestrians, transit and drivers all travelling in the same direction.

Decisions about phases, and how long they last, take into account actual traffic volumes and how traffic patterns change throughout the day. Timing is designed to make the intersection work as efficiently as possible [meaning moving through the largest numbers of users], and minimize delays for all road users [although with many roads at or over capacity during rush hour, signal timing alone can’t solve congestion]. Signal priority is also provided to fire, ambulance and transit, where the signals change to provide priority right-of-way to emergency vehicles and some transit vehicles, without violating the pedestrian timings.

Timing for each phase is based on the minimum timings required by provincial standards. These include minimum timings for pedestrians, motorist and vehicle clearance [amber and red timings] based on several factors, including the width of the intersection, and traffic speed [posted and operating].

Proximity to other infrastructure also has an impact on priorities and the timing of phases. For example, the Ontario Ministry of Transportation may have jurisdictional control over the timing of lights at some intersections, depending on how close the intersection is to a provincial highway off-ramp or railway crossing.

Ultimately, any one cycle has only so many seconds, and no one wants to wait longer than they have to. So the design of traffic signals needs to balance everyone’s needs, while working out the best way to move traffic through an intersection and along a thoroughfare, and minimizing delay for all road users. York Region’s Traffic Signal Operations department continually reviews and assesses the performance of the region’s 848 signalized intersections, and adjusts signal timing to get people moving as freely as possible. Please contact traffic@york.ca if you have any traffic signal concerns.

Whether you’re crossing intersections on foot, bus, bike or car, traffic signals are there to move everyone along safely.