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Traffic Count Mapping – About Traffic Counts
OVERVIEW • DATA • TRAFFIC COUNT MAPPING • ADDITIONAL RESOURCES
Overview • Popup Task Guides • About Traffic Counts

What are traffic counts?


Traffic counts collected by the MPO come in a number of different "flavors," although the interactive maps only show ADT:
  • "Volume" is the sum of all vehicles in a unit of time, usually an hour
  • "Peak volume" is the sum of all vehicles in a peak period ("rush hour")
  • "Average daily traffic" (ADT) is the total traffic during a period divided by the number of days in that period. A count made over a few days may be adjusted to represent an average for the year by accounting for seasonal and weekly variations in traffic
  • "Average weekday traffic" (AWDT) is the total measured on several during a weekdays divided by the number of weekdays. The average may be adjusted in the same way ADT is adjusted.
  • Classification counts measure different types of vehicles (i.e., motorcycles, cars, light trucks, three-axle trucks, etc.) in a unit of time
  • Speed counts tally the vehicles in different speed ranges in a unit of time
  • Turning movement counts tally the vehicles making each possible turn at an intersection in a unit of time. Pedestrians and bicycles may also be counted.

Why are traffic counts collected?

  • Traffic count data may be used to support an argument for road improvements, including reconstruction, when they prove that large numbers of vehicles are subject to unsafe conditions or are causing congestion and delays.
  • Computer models must be calibrated using traffic counts in order to predict the region's future traffic with any degree of accuracy
  • Various laws and regulations mandate the collection of traffic counts:

Where are traffic counts collected?


In principle, traffic counts can be collected almost everywhere—in tunnels, on bridges, on superhighways, and on private dirt roads. The location of traffic counts is chosen by the collecting agency and the agency that has legal jurisdiction over the facility being measured.

Because the MPO primarily collects traffic-count data conducted by the Massachusetts Highway Department, the locations reflect that agency´s particular needs. Most are on principal roads and major state and federal highways, with thorough coverage of interstate highways.

What time periods do traffic counts cover?


Traffic counts have been collected since the dawn of the automobile era, but traffic counts in electronic form first appeared in the mid- to late 60s. In limited cases, earlier counts on paper have been converted into electronic form. The MPO´s earliest electronic data are from 1962, permitting valuable longitudal studies to be conducted.

At some locations, traffic counts are collected on a continuous, 24-hour-per-day, seven-days-a-week basis. However, most traffic counts are collected over a fairly short span of time (two or three days, or even one morning and one evening rush-hour period). The collection may be repeated at intervals (a few years apart, for example), but is often a one-time event at a particular location.

Who collects traffic counts?


State and regional government agencies and private engineering consultants are responsible for conducting most traffic counts. Although private citizens can certainly count vehicles using pencil and paper, most vehicle counts involve costly automated equipment and the permission of a roadway owner or operator.

The MPO´s traffic-count data are primarily from the Massachusetts Highway Department, which uses its own equipment and staff as well as those of regional planning agencies across the state. The MPO collects some turning-movements (see the section on what kinds of traffic counts there are) itself, and may also collect paper copies of traffic count data from other sources.

How are traffic counts collected?


Most traffic counts in Massachusetts are collected in one of three ways:
  • A sensor permanently embedded in the pavement detects the passage of vehicles using electrical methods. The signals are interpreted and recorded by a roadside equipment box, visited periodically by an engineer. These sensors are found where continuous, year-round monitoring is important.
  • A number of rubber hoses temporarily stretched across the roadway detect the passage of vehicles when their wheels compress the air in the hoses. The air pressure changes are interpreted and recorded by a roadside equipment box that is collected by an engineer. This type of equipment is best used when there is no risk of snow removal disturbing it.
  • A human operator uses a special console to record different types of traffic for later transfer to a computer. The console is like an expanded version of the clickers used to count attendees at large events. This last method is typically used for turning-movement counts (see this section for more explanation of turning-counts).
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