System Performance

System Performance seeks to evaluate the effectiveness of the Interstate and non-Interstate National Highway System (NHS) for the purpose of carrying out the National Highway Performance Program (NHPP). The federal rules on TMP measures for system performance require establishment of targets every 2 and 4 years, respectively. Since targets were first established in 2018, SEMCOG, in cooperation with MDOT, has updated the targets as required. Targets must be established on the National Highway System (NHS) throughout the state (FHWA).The NHS includes 7,381 lane miles of road in the SEMCOG region. MDOT owns 62.4% of those lane miles.Federal regulation requires that MPOs establish targets for the performance of three areas:

• National Highway System (NHS) Travel Time Reliability
• Freight Reliability
• Congestion Mitigation and Air Quality Improvement (CMAQ)

National Highway System (NHS) Travel Time Reliability

Federal System Performance measures use vehicle speed data to quantify the reliability of travel on Interstates and the non-Interstate National Highway System (NHS). Two- and four-year targets are set for:

• Percentage of person miles traveled on the Interstate System that are considered reliable.
• Percentage of person miles traveled on the non-Interstate NHS that are considered reliable.

The two measures shown above express the percent of person-miles traveled on roads that are reliable. These measures attempt to instruct travelers how often they can expect to travel in reliable conditions. A road is considered reliable when the difference between normal travel times (50th percentile) and congested travel times (80th percentile) is below 50 percent. In other words, a road segment that takes one minute to travel under normal conditions would be considered reliable if the time it takes to travel under congested conditions is less than one and a half minutes.

Freight Reliability

Freight reliability is assessed by a Truck Travel Time Reliability (TTTR) Index. This is used to determine the consistency or predictability in travel times for trucks on specific routes of road segments (FHWA). Reporting is divided into five peak hour travel time periods which include peak daytime periods, an overnight period, and weekend periods. The TTTR ratio is measured by the ratio of congested peak period travel time (95th percentile) and the normal peak period (50th percentile) for each segment on the interstate system. The highest TTTR value is used to determine the reliability of the Interstate system for truck traffic or freight reliability. SEMCOG establishes two- and four-year targets for:

• The ratio of the congested period travel time to the normal period travel time, weighted by the length of the Interstate segment, for the entire Interstate system in the state.

CMAQ Program

The federal rules on performance management measures for CMAQ require establishment of performance targets every 2 and 4 years, respectively. As these targets were first established in 2018, SEMCOG, in cooperation with MDOT, has updated the 4-year targets as required. Targets must be established for urbanized areas with populations greater than 200,000 with any part of a designated nonattainment or maintenance area for criteria pollutants. For the SEMCOG region, this includes the urbanized areas of Detroit, Ann Arbor, and, Toledo, OH.

Three measures are established to assess performance of the federal Congestion Mitigation and Air Quality (CMAQ) program.

• On-Road Mobile Source Emissions: Total Emission Reductions
• Traffic Congestion Annual Hours of Peak Hour Excessive Delay Per Capita
• Traffic Congestion: Percent of Non-Single Occupancy Vehicle (SOV) Travel

On-Road Mobile Source Emissions is an assessment of the effectiveness of the Congestion Mitigation and Air Quality (CMAQ) program in reducing emissions from on-road motor vehicles. These measures are required for each criteria pollutant that is designated as nonattainment or maintenance, which for Southeast Michigan includes carbon monoxide (CO) and fine particulate matter (PM 2.5).

The Peak Hour Excessive Delay (PHED) measures the duration of severe congestion on freeways and arterials in Southeast Michigan. Data for this measure uses probe speed data from personal and vehicular connected devices. PHED is the cumulative time roadway segments are operating either below 20 miles per hour or below 60 percent of the posted speed limit. To have the measure be closer to the impact on an individual peak-hour traveler’s life, the total cumulative delay for a road segment is divided by the number of vehicles traveling on that segment. PHED factors in both highway travel speeds and travel volumes.

Percent Non-Single Occupancy Vehicle (SOV) Travel measures the proportion of trips that use travel options that reduce vehicular trips through carpooling, vanpooling, transit, walking, biking, or telecommuting. Increasing the number of people choosing non-SOV travel helps reduce congestion and air pollution. Increasing non-SOV travel reduces the number of vehicles running in the region while providing travel alternatives to people who want to reduce solo travel and people without access to a private vehicle.

National Highway System (NHS) Travel Time Reliability Targets

Interstate Freight Reliability Targets

Congestion Mitigation and Air Quality (CMAQ) Targets

The federal rules on performance management measures for CMAQ require establishment of performance targets every 2 and 4 years, respectively. As these targets were first established in 2018, SEMCOG, in cooperation with MDOT, has updated the 4-year targets as required. Targets must be established for urbanized areas with populations greater than 200,000 with any part of a designated nonattainment or maintenance area for criteria pollutants. For the SEMCOG region, this includes the urbanized areas of Detroit, Ann Arbor, and, Toledo, OH.