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Mobility Monitoring – Roadways – Overview
OVERVIEW • REGIONAL TRENDS • ROADWAYS • INTERSECTIONS • TRANSIT
BICYCLE/PEDESTRIAN • HOV LANES • TRAVEL DEMAND MANAGEMENT • PARK-AND-RIDE
Overview • Arterial Roadways • Crashes • Freeways • Performance Measures • Traffic Volumes
Approximately 16 million trips are made in the Boston metropolitan region every day. The vast majority of these trips (80 to 85 percent, depending on trip type) involve the use of the roadway network (including trips driving to a transit station and carpools). About 80 million vehicle-miles are logged every day, over three quarters of these on the interstate highways and arterial roadways, even though these types of roads account for only a fifth of the centerline miles of the entire roadway network.

The Monitored Network
Travel time information is collected on the regionally significant roadways in the Boston region. These include all roadways that are functionally classified as principal/major arterials and all limited-access highways (often called expressways or freeways), as well as some minor arterials. This network comprises about 900 centerline miles (or 1,800 bidirectional miles) of arterial roadway and 377 centerline miles of limited-access highway – over 10 percent of all roadways in the region. Most state-numbered roadways are included in the monitored network, as are most corridors of the National Highway System.

In general, volumes on these roadways exceed 10,000 vehicles per day. Most of the arterial roadways typically handle over 27,500 vehicles per day on some portion of their length. Volumes on the limited-access highways in the Boston region typically range from 40,000 to 235,000 vehicles per day.
How Are the Data Collected?
Travel time data are collected using a probe vehicle that travels with the flow of traffic according to the “floating car” technique. Each probe vehicle is equipped with a global positioning system (GPS) and with a data collection device (laptop or palmtop computer) that records travel times and distances at one-second intervals. For each roadway segment, a valid sample size of travel time runs is obtained in order to calculate a significant average peak-period measurement. A segment usually begins immediately after a significant intersection and ends immediately after the next significant intersection.

The roadway monitoring captures typical traffic conditions during commute times. Roadways are monitored during weekday morning and evening peak commute periods, primarily between 6:30 AM and 9:00 AM and between 3:30 PM and 6:30 PM. Monitoring does not occur on weekends, Monday mornings, or Friday evenings; nor does monitoring occur during the peak period following or preceding a local, state, or national holiday. Monitoring is conducted during the public school year, in the spring and the fall seasons.