What is the Mobility Monitoring Program?
The Mobility Monitoring Program is an effort by the Federal Highway Administration (FHWA) to track and report traffic congestion and travel reliability on a national scale. The program has two primary objectives:
- Monitor traffic congestion levels and travel reliability trends using archived traffic detector data; and
- Provide “proof of concept” and technical assistance to encourage local/regional performance monitoring programs.
The Program uses archived traffic detector data that were originally collected for traffic operations purposes. Thus, the extent of the Program is limited to those cities and roadways where real-time traffic data are collected and archived. The Program started in 2001 (with an analysis of 2000 data) in 10 cities. In 2004, the Program has grown to include nearly 30 cities with about 3,000 miles of freeway. The Texas Transportation Institute and Cambridge Systematics, Inc. support the Mobility Monitoring Program activities.
What Performance Measures are Used?
The Program monitors traffic congestion using these measures:
- Travel time index — the ratio of average peak travel time to a free-flow travel time (in this report, the travel time at 60 mph for freeways). For example, a value of 1.20 means that average peak travel times are 20 percent longer than free-flow travel times.
- Percent of congested travel — the ratio of congested travel to total travel. The analysis uses vehicle-miles of travel (VMT); person-miles of travel could also be used if person flows are of interest and widely available. The percent of congested travel is a relative measure of the amount of travel affected by congestion.
- Delay — the additional travel time that is incurred when actual travel times are greater than free-flow travel times. The delay is expressed in several different ways, including total delay in vehicle-hours, total delay per 1,000 VMT, and share of delay by time period, day of week, or speed range.
The Program includes these measures for travel reliability:
- Buffer index — the extra time (buffer) most travelers add to their average travel time when planning trips. For example, a buffer index of 40 percent means that a traveler should budget an additional 8-minute buffer for a 20-minute average peak travel time to ensure on-time arrival most of the time (95 percent in this report).
- Planning time index — Statistically defined as the 95th percentile travel time index, this measure also represents the extra time most travelers add to a free-flow travel time when planning trips. For example, a planning time index of 1.60 means that travelers plan for an additional 60 percent travel time above the free-flow travel time to ensure on-time arrival most of the time (95 percent in this report).
The Program also tracks throughput (an “output” measure) using peak-period and total daily VMT.
What Data are Used?
The Mobility Monitoring Program uses archived traffic detector data that were originally collected for traffic operations purposes. Thus, the extent of the Program is limited to those cities and roadways where real-time traffic data are collected and archived. This real-time traffic data is typically collected in those cities and roadways where traffic congestion is a daily problem. Nearly all of the data used in the Program are from freeways.
The archived traffic detector data is more detailed than data typically collected for traditional traffic congestion studies. Roadway or roadside sensors collect traffic volumes and speeds in every lane at ½-mile to 1-mile intervals. The real-time traffic data are typically sent from a field computer to a central database every 20 seconds to 1 minute; the data may later be aggregated into 5-minute summaries for permanent storage. The data typically are collected 24 hours each day, 365 days per year. The data are later grouped into several time periods for reporting, and most congestion and reliability measures are presented for peak traffic periods.
Where Can I Find More Information or View City-Specific Reports?
More information on the Mobility Monitoring Program can be found at http://mobility.tamu.edu/mmp/. The Program has produced annual summary reports as well as city-specific reports since 2001, and the most recent reports are available at this website. In October 2004, the Program began producing monthly reports to provide more timely trend information to FHWA. These monthly reports are available on request.
What Do We Know After 4 Years of Monitoring Traffic Congestion and Reliability?
We offer the following observations:
- From 2000 through 2003, average traffic congestion and reliability levels appear to have gotten worse in numerous cities. The trend analysis is complicated by increasing freeway coverage. Additional analyses that accounted for increasing freeway coverage indicate the possibility of little significant change in the peak periods, with delay growth being more significant in the times and days outside of the defined peak period (weekdays, 6-9 a.m. and 4-7 p.m.).
- In most cities, travel reliability appears to be strongly correlated to traffic congestion. The nature of this relationship varies among cities, but preliminary hypotheses suggest that aggressive freeway operations and management contributes to improved reliability for similar average congestion levels.
- The approach used in this Program can also be used by State and local agencies. In fact, several agencies already have implemented similar analytical methods and/or performance measures.
- There are still several issues that, if addressed, could improve the process and results. One of the most important issues to address is improving data quality at the data collection source.