Advisor, International Road Dynamics
One of the most visible components of the Smart City is the traffic management system, with traffic sensors doing the behind-the-scenes work to power these systems. Think of traffic sensors being the seven-eighths of the iceberg under the water. While the one-eighth above the water gets all the attention, it is the traffic sensors below the water that act as a foundation to hold it all up. Sensors work silently and efficiently in the background to provide the foundational data for all the neat things we can do in traffic management and smart cities.
What makes for detection perfection? Let us start by looking at sensor systems for intersections. These are typically deployed when traffic signals are used to control the traffic at an intersection. From an engineering point of view, an intersection represents a potential conflict between different traffic streams. There are two ways that you can resolve this conflict – space or time separation. Space separation involves a whole lot of money to build a concrete and steel overpass that effectively separates the conflicting traffic streams. Time separation is more commonly referred to as traffic signal control. We share the amount of time available at the intersection according to a plan that enables all flows to operate effectively.
An important aspect of traffic signal control lies in ensuring that the amount of time offered to an intersection approach is consistent with the varying traffic volumes through the intersection. This is often referred to as adaptive traffic signal control. Of course, to effectively adapt traffic signal timings to the variations in flow through the intersection, it is necessary to sense or detect traffic, pedestrian, and bicycle flows at the intersection.
There are several different ways to sense traffic at an intersection. These include the established approach of installing loops of copper wire into the road surface. When a voltage is applied, an inductive field is generated above the road. As vehicles cut the inductive field, variations in the voltage can be detected and represented as a vehicle. Another variation on this theme is the use of a device about the size of a hockey puck to generate the inductive field, with wireless communications to a roadside controller. Both approaches can be considered as intrusive detection since the roadway surface has to be cut to insert the sensing devices.
More recently, a nonintrusive approach has emerged, in the form of video image processing and microwave sensors for traffic control which are installed above the intersection and require no damage to the roadway for installation or maintenance. The benefit is to simplify and minimize (or eliminate) the need for traffic control.
So, what exactly would detection perfection look like? Here is a table that summarizes a few important factors and compares the different technology approaches:
When selecting an appropriate sensor for a specific purpose in transportation management, it is important to take a complete view on the quality aspects of the sensor. While inductive loops have a history of delivering the highest accuracy with respect to traffic signal control detection, they also have an Achilles’ heel with respect to downtime. If a sensor is not online, then it does not matter how accurate it is. The nonintrusive techniques described can deliver accuracies approaching those of the inductive loops but do not suffer from the problem of downtime and unavailability. A fair and complete approach to sensor assessment would be to apply a quality index. This would represent a combination of accuracy and availability and should indicate that nonintrusive techniques, particularly microwave, are much more effective, when this balanced view is taken.
IRD as a leader in the fields of sensing, traffic management and truck compliance, recently extended its product offering to include superior microwave detection products. This new line of iCOMS presence detection sensors can be deployed at intersections to supply data for traffic signal control or along highway links to provide additional data for traffic engineering and transportation planning. Of course, both uses can feed into a bigger picture of smart data management for a smart city. ICOMS products represent a cost-effective approach to nonintrusive sensing on urban streets. ICOMS sensors address most, if not all, of the parameters listed above when defining detection perfection. iCOMS sensors are nonintrusive, have no moving parts and are robust in operation under different weather conditions. They have the flexibility to be applied to both intersection and highway link locations in a cost-effective manner.
In Part 2 of Detection Perfection, we will take a closer look at what sensors mean to the Smart City.Back