TP&T keeps a library of hundreds of traffic counts of all types. Traffic counts have many uses in traffic engineering. They are used to set the timing of traffic signals, determine the number of lanes needed at an intersection or along a street, calculate crash rates, and to gauge the growth (or decline) in traffic over time.
There are two main sources of traffic counts: traffic impact studies and the Street Management Division itself. Traffic impact studies are usually required of any land development project larger than a certain size. Traffic counts are an important part of those studies. We now require that vehicle, pedestrian, and bicycle counts are conducted for every intersection included in the study. Second, the Street Management Division conducts our own counts as part of smaller traffic studies requested by residents or as part of the Division’s safety evaluation program.
The type of traffic counts in our library are intersection counts, roadway segment counts, truck counts and speed studies.
Engineers conduct Turning Movement Counts (TMCs) at intersections manually by tabulating each movement (left, through, and right) from every street approaching the intersection. For the past several years we have been counting pedestrians and bicycles along with vehicles. The counts are usually taken for two hours each for both the morning and afternoon rush hours. On occasion we will count the Saturday peak as well.
Traditionally, TMCs were taken by hand by a technician watching the intersection in person using an electronic tabulating machine. Today it is more economical to take TMCs instead with a video recording device and analyzed in an office setting later. These low-resolution cameras are mounted high with fish-eye lenses and are able only to allow the analyst to see movement of each mode. They cannot see license plate numbers or faces.
Road Segment Counts
While TMCs can tell us the activity within an intersection during the rush hours, a road segment count tells us the level of activity on a road for an entire day, or even several days. Automatic Traffic Recorders (ATRs) log every vehicle that passes in each direction, from which we calculate daily traffic volumes for the street.
ATRs have two components. The first are rubber hoses temporarily affixed to the street. When a vehicle passes, a pulse of air passes through the hose and triggers an air switch in the recording device on the roadside. The recording device is a small steel box powered by a battery. Air switch triggers are stored on board and are later downloaded to a computer.
Traditional ATRs are not able to record bicycles, however TP&T has launched a program to count cyclists at permanent count stations.
Permanent Count Stations
TP&T installed its first permanent count station in 2013. The station uses traffic-grade low-resolution cameras mounted to poles above the road. The device is configured to count and distinguish between vehicles in the travel lanes and bikes in the bike lane. It has no video recording device and is not attached to any video monitor. The on-board storage is able to record only the numbers of each unit that passes the count station in each hour. The station counts 24 hours a day, 7 days a week, 365 days a year.
Count data from our count stations are available in our data section.
Availability of Traffic Count Data
Data in our library dates back to the mid 1980s. Some of these counts are in electronic form and available in our data section. Others are still on paper, usually as part of the appendix to a traffic study. Counts currently available in our data section are:
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