SmartSensor HD - Interprovincial Traffic Services

CHAPTER 7 • DATA SETUP AND COLLECTION 73NoteIf the volume in the interval is zero, and the occupancy is less than 20%, the speedin the interval will be the speed of the previous interval. If the volume in the intervalis zero, and the occupancy is more than 20%, the speed in the interval will be zero.The interval data screen displays the following information for each lane or approach, dependingon which tab you’ve selected (to see all columns, use the cursor to click and dragthe screen to the right or left):˽˽Name – Displays the name of each lane or approach. To change the name, go to theLane Configuration screen or the Approaches screen.˽˽Volume – Shows the number of vehicles detected during the interval.˽˽Occupancy – Gives the percentage of time during the interval that the detection zonewas occupied.Occupancy is calculated by summing the durations of all vehicles in the interval and dividingthat quantity by the length of the interval. For example, if the interval length is fiveminutes and 100 vehicles pass the sensor during the interval with a duration of 0.09 secondseach (sum of the durations is 9 seconds), then the occupancy for that interval wouldbe calculated by dividing 9 seconds by 300 seconds, which is 3%.Before summing the vehicle durations, compensation is applied to the durations to removethe width of the antenna beam at the vehicles’ range and to add the loop size. The purposeof this compensation is to make the occupancy measurement consistent over the wholerange of the sensor and to make the occupancy measurement comparable to an occupancymeasurement generated by a loop the size of the loop size setting.The following equation represents the occupancy calculation described above:1Interval Size*∑Vehicle Duration * Vehicle Speed - Antenna Beam Size + Loop SizeAll Vehicles inVehicle Speedthe Interval˽˽Speed – Indicates the average lane speed during the interval. A negative number willbe reported for speed in the following cases: (1) The lane was configured to the leftor right and Direction Protection was on, but traffic was traveling against the configureddirection, indicating that the direction of the lane has switched. This is useful inhurricane evacuation scenarios. (2) The lane was configured to the left or right andDirection Protection was off, but more vehicles were detected traveling against theconfigured direction than were detected traveling with the configured direction for thegiven data interval.Unlike per vehicle data, lanes that are configured as bidirectional will always reportpositive average speeds in the interval data.