Traffic sensors detect (count) the road users that are moving in the signal-controlled junction or pedestrian crossing. They are necessary for the assurance of the adaptive operation of the junction, so that the traffic flows are regulated as efficiently as possible (in order to ensure the highest possible capacity of the transport flows and to minimize the time road users spend standing at the junction). Moreover, sensors are necessary for the calculation of traffic flows (collection of statistics). All data collected from the sensors is stored in the server and used for traffic flow analysis, traffic management planning, and optimization.
Two types of sensors are used in Vilnius City: transport sensors that are divided into three categories (inductive loops, vision sensors, and infrared sensors) and the buttons for pedestrians and cyclists.
Vision sensors operate based on the principle of image recognition. The vision sensor is a video camera configured using special software: a virtual zone is placed on the surface of a virtual street (portion of the street’s area) whose purpose is to recognise a vehicle. As a vehicle goes through this zone, it is detected (counted). During programming, the direction of the vehicles that are to be detected (recorded) is also specified. When programming the video sensors, it is necessary to also take other factors into account such as sensor sensitivity, location, detection angle, distance to the carriageway, and the width of the detected traffic lanes. Proper maintenance of the vision sensors and software updates reduce the margin of error in the calculations of transport flows.
Inductive loops operate based on the principle of electromagnetic detection: a vehicle that goes through an inductive sensor embedded in the road surface generates an electromagnetic impulse which is processed by the junction controller and counted as a unit of the transport flow. The processed data is sent to the server of the Traffic Management Centre.
The infrared sensor’s operating principle is based on the detection of vehicles by the measurement of their infrared radiation emitted from the selected detection zone (the number of detection zones in the sensor is equal to the number of traffic lanes in which it is calculating the traffic flows). Vehicle detection ignores slow changes in road surface temperature caused by the changing weather condition. Infrared sensors are suitable for counting not just vehicles but also motorcycles, bicycles, and pedestrians.
Buttons for pedestrians and cyclists in Vilnius City are touch-based, i.e. you just touch the button with your palm, and the caption “Laukite” (“Wait”) lights up on its upper part.
The pedestrian buttons in the newly designed or reconstructed junctions and pedestrian crossings are adapted for partially-sighted persons. They have an elevated directional arrow placed on the button’s frame and give an additional audible signal at a red light. If a sensor-based button adapted for partially-sighted persons is installed, it has the function of button push confirmation (audible signal or vibration).
It does not matter at all how many times you push the button for pedestrians or cyclists. One push is enough for the junction controller to react to your query. The number of pushes does not determine how soon the light will turn green for pedestrians or cyclists;
It is important to remember that the waiting times for the green light after pushing the button vary in different junctions: if there is one or multiple junctions near the junction (pedestrian crossing) which is being crossed, the operation modes will be synchronised between the nearby junctions and the transport flows will be coordinated between them as well. This kind of traffic management method is called partial adaptivity of a junction. Therefore, after pushing the button, a pedestrian or cyclist will receive permission to cross the street not immediately, but at a pre-determined time. In such a case, the pedestrian’s or cyclist’s maximum waiting time could be up to 110 seconds (during the peak hours). If another traffic management method is used (complete adaptivity of a junction), the pedestrian’s or cyclist’s waiting time could be cut down significantly to the duration between 0 and 50 seconds. This traffic management method is possible in individual junctions or pedestrian crossings where the junctions’ operating modes are not synchronised with one another