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Optimize System Performance

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Congestion and Reliability Indexes

Description: Measurement of average traffic congestion and travel time on Texas roadways.

What is the trend?: (CY 2016 to CY 2017 comparison)

  • Urban congestion: Performance Declining red arrow going up
  • Urban reliability: Performance Declining red arrow going up
  • Rural reliability: Performance Stable yellow flat line
  • Truck reliability: Performance Stable yellow flat line

How it is measured: Several indexes are used to measure congestion and travel time in the state. The congestion and reliability indexes are:

  1. Urban congestion
  2. Urban reliability
  3. Rural reliability
  4. Truck reliability

The urban reliability index is the ratio of the 95th percent peak-period travel time (“rush hour”) to free-flow travel time (when traffic flows at the speed limit) in areas with populations over 50,000. The 95th percent is an indicator of the heaviest traffic time period. This index is useful as a trip-planning tool for drivers for understanding the longest amount of time it could take to drive to their destinations.

Example: A vehicle in Austin leaves home to travel downtown on a Monday morning at 8 a.m. through heavy traffic, and the travel time is 30 minutes. On Saturday at 8 a.m., the vehicle makes the same trip from home to downtown, able to drive the speed limit, and completes the trip in 20 minutes. The resulting urban reliability index is 1.5 (30 minutes divided by 20 minutes).

The rural and truck reliability indexes are variations of the urban reliability index. Rural areas are those with populations below 50,000. Truck refers to commercial trucks only.

The urban congestion index is calculated similarly to the urban reliability index, except instead of the 95th percent peak-period travel time, it uses the average travel time for the full year.

Why this matters: Transportation empowers us all and affects every aspect of our daily lives. Most people must travel to school, to work, to obtain necessities or medical care, and for social reasons. Of the many factors driving increases in transportation demand, population is one of the larger. The Texas Demographic Center estimates that from 1990 to 2008, the population of Texas increased by an estimated 6,627,987 people, a 39 percent increase. Texas‘ population is forecast to grow an additional 10,175,200 people by 2035, a 43.1 percent increase. Tracking travel times throughout Texas assists in identifying top areas of congestion and hot spots for TxDOT to focus on improving overall reliability.

Vehicle Miles Traveled

Description: Number of miles traveled by vehicles (passenger and commercial truck) on Texas roadways.

How it is measured: Vehicle miles traveled is the total mileage traveled on Texas highways in a year.

Why this matters: The total mileage on our highway system is a reflection of population growth and driver behavior in our state. It is included in TxDOT performance measures as its result directly influences the congestion and reliability indexes, or other performance measures being tracked as part of TxDOT’s Strategic Goal: Optimize System Performance.

Annual Delay Per Person

Description: Measurement of the hours of delay for a driver on Texas roadways.

What is the trend?: (CY 2016 to CY 2017 comparison)

  • Annual delay per person: Performance Improving green arrow going down

How it is measured: Annual delay per person is the ratio of the total annual hours of delay for all vehicles on Texas roadways to the estimated population of Texas (population estimates are sourced from the Texas Demographic Center). This measure calculates the estimated annual delay per person for the state inclusive of passenger vehicles and commercial trucks.

Why this matters: The highway system in Texas serves the growing needs of an ever-changing and increasingly diverse traveling public. Hours of delay on Texas roadways incurs time and cost for our growing business sector and population. Tracking the delay assists in managing the improvement in relieving bottlenecks and enhancing the efficiency of the transportation system.

Optimize System Performance

Develop and operate an integrated transportation system that provides reliable and accessible mobility, and enables economic growth.

Objectives for goal:

  • Mitigate congestion.
  • Enhance connectivity and mobility.
  • Improve the reliability of our transportation system.
  • Facilitate the movement of freight and international trade.
  • Foster economic competitiveness through infrastructure investments.

Performance measures for goal:

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