Frequently Asked Questions

TTI logo
  • What year is the data?
    The 2020 Texas 100 list uses data from 2019.
  • Does this analysis reflect the effects of the pandemic?
    No, these data were collected before the COVID-19 pandemic affected congestion levels in early 2020.
  • Why is Texas 100 done?
    In response to increased roadway congestion throughout the state, in 2009 the Texas Legislature mandated that the Texas Department of Transportation (TxDOT) annually produce a ranked list of the most congested roadways in the state to help focus attention on some of the worst bottlenecks in the state.
  • How is information from Texas 100 used within TxDOT?
    Texas 100 Most Congested Road Section ranking is used as part of TxDOT’s statewide project selection and scoring analysis to help determine a project’s need as it relates to congestion. The Texas Clear Lanes Initiative is focused on identifying, funding and building projects that address the top 100 of the Texas 100 rankings.
  • Why is delay per mile the key measure used to rank the sections?
    Person-hours of delay per mile (and truck delay per mile) are used as the primary performance measures for the rankings for several reasons.

    • Delay-based measures identify the biggest problem areas because they combine the performance of the roadway segment (speed data) with how many travelers are impacted by those speed conditions (traffic volume data).
    • In general, delay measures are advantageous because they capture the full extent of the congestion problem because they are computed for every hour of every day throughout the year (“24/7/365”).
    • Dividing the total delay for a segment by the segment length allows roadway segments that are different lengths to be compared. If you didn’t divide by the length, the longer sections would have more volume, more delay and be nearer the top of the list just because they were longer.
  • Why can I not compare this year’s measures to previous year’s?
    While this would be the perfect situation in congestion monitoring across Texas, there are several reasons why we recommend not doing this.

    • The data has changed – both the TxDOT traffic volume and the speed data from the private sector data provider.
    • TxDOT has been improving their traffic count database (both all-vehicle and trucks) over the last few years. Some of the traffic volume changes from year-to-year are due to the quality improvements, not actual changes in traffic volume.
    • The same quality improvements have taken place in the traffic speed information. INRIX (the provider determined by a competitive bid process) is constantly improving their speed dataset by changing, updating and expanding their maps. The roads where speed data are available and the quality of the data provided affect the performance measure calculations.
    • The source of the speed data has also changed. The data is obtained from a combination of global positioning systems installed in cars and trucks, and cell phones carried by those looking for traffic information. The data stream several years ago was primarily from devices used to efficiently route trucks; the vehicle mix now contains many more cell phones and passenger cars. While car and truck speeds usually only differ by a few miles per hour, the more cars that are added to the dataset, the faster the average speeds become.
    • Because these improvements vary in amount from year to year, the congestion measure values can show an improvement or deterioration in a section of road that may not have been experienced by motorists.
    • The Texas 100 database tracks the rankings from year to year – those tend to be better indicators of the congestion changes regardless of the types of data and methodology changes.
  • How much do rankings change from year to year in the list?
    Sections of road near the top of the list (top 25) tend to stay near the top of the list because congestion is intense and occurs during many hours each weekday and during some hours of the weekend. Sections outside the top 25 tend to have congestion in one direction in the weekday morning and the other direction in the evening. Road sections in the bottom half of the Top 100 may bubble in and out of the Top 100 because congestion changes on these roadways is often caused by nearby office, retail or commercial developments and road construction on the corridor itself or on a nearby parallel or intersecting facility. These traffic changes can be permanent or temporary; before solutions are considered, it is important to understand the causes.
  • Has the methodology changed for Texas 100?
    The general methodology used to calculate the Texas 100 statistics has been virtually the same since the 2010 report—the first report in the series to make use of the private-company speed datasets. However, the quality of the data (both private sector speeds and the roadway inventory) has improved due to expanded coverage and completeness of the input datasets.
  • What data is used?
    The traffic and road data come from TxDOT’s Roadway-Highway Inventory (RHiNo) database that includes roadway inventory information such as traffic volumes, truck volumes, number of lanes, etc.
    The speed data for the 2020 list was obtained from INRIX, a private sector company specializing in providing travel information data from a variety of sources.
  • How many sections of road are tracked?
    The 2020 Texas 100 list contains 1,860 sections of road covering about 9,900 miles of Texas roads.
  • How were these sections chosen?
    The first few years of the Texas 100 list included 500 sections of roadways that had the highest traffic counts in the state. These locations were generally in the four large metropolitan areas of the state. However, the list was expanded to include sections of road in all of the urban areas across the state using input from local transportation agencies. The 2020 list contains just under 10,000 miles of road.