Blog | January 31, 2022
Data & Analysis - Texas highways and roads
Questions arise every year on how many miles of roads there are in my county or state? Which county has the most miles of roads? Who has the most miles of dirt roads? Though these were once very difficult questions to answer, there now is a reliable source for the data.
The Texas Department of Transportation (TxDOT) produces an annual report, a Roadway Inventory, on the roads and highways in the state. The report includes a table that covers the number of centerline and lane miles of roads by county broken down by type of road — part of which we include with our County Profiles (www.txcip.org).
TxDOT breaks down the roads into two groups. First, there are "on-system" roads, meaning those roads that fall under the state's jurisdiction. This includes many of the miles of federal highways in the state, but not all of them.
Other roads, many of which belong to local jurisdictions such as cities and counties, the state labels "off-system". Chart 1 shows the number of centerline miles of roads and highways in the state from 1970 to 2020. Total miles, which includes both on-system and off-system roads, are in blue; but, as the breakdown shows, most of those miles are from off-system roads. By comparison, the on-system miles are show in green and account for less than half of the total centerline miles.
Changes in definition and/or methodology over this period partially explain the changes in mileage. For example, the mileage from 1970 to 2006 includes both roads open to traffic and those under construction. In 2007, the state changed the methodology to count only those miles open to traffic. In addition, in 2017 the state transitioned to a new roadway inventory database system called GRID. During the prior two years, the transition affected the state's estimates of mileage, which partially accounts for the plateauing of miles from 2014 to 2016.
Over the same 51-year period, the estimated number of miles vehicles traveled on roads within Texas increased dramatically, as seen in Chart 2. Total miles traveled increased steadily until 2007 before dropping off in 2008, as the housing price crash hit the state. In 2009, the miles began to pick up again before peaking in 2019 at an estimated 790 million miles per day for all types of vehicles on all types of roads in Texas. Even though there was a clear drop-off in 2020, the estimated number of vehicle miles traveled per day had increased by 282% since 1970. The number of miles traveled solely on off-system roads, which includes county roads, had increased by 301%, while TxDOT estimated the miles traveled over on-system roads (not shown) had increased by 275% over the same period.
TxDOT produced similar estimates for the number of daily miles traveled by trucks. Its report provides those estimates only as far back as 1990, as seen in Chart 3.
Curiously, while the growth rate seems to slow slightly after the 2001 market crash, it doesn't decline until 2008 after the housing price crash. With the start of the shale oil boom in 2009, estimated daily truck mileage begins to grow again before really taking off in 2013 and then peaking at 83 million miles per day in 2019. The number of active drilling rigs in the U.S., which had been in decline since around mid-2018, dropped significantly in 2019 before taking a steep nosedive in 2020, according to the Nov. 16 Energy Indicators report from the Federal Reserve Bank of Dallas. More recently, the number of active rigs in the U.S. began to increase, reaching 557 by October 2021 — a strong number but still well below the more than 1,000 active rigs in mid-2018.
There are more miles of off-system roads in Texas than on-system roads, including highways, even though much of the daily traffic happens on the on-system roads. For some people the greater traffic leads them to believe that the on-system roads are of greater importance. But how would food get from the farms and ranches without those off-system roads? How would urbanites get to the rural parks and natural areas or even to their local grocery stores? There is no doubt that both on- and off-system roads are important to all of us.
Centerline miles: Mileage of the road regardless of the number of lanes. One mile of a two-lane road counts for the same number of miles as one mile of a four-lane highway. However, the state counts frontage roads separately from the main highway even though they may extend over the same distance as the main highway.
Lane miles: The state counts the miles of each lane — but only in one direction. Therefore, one mile of a two-lane road stretches twice as far as one mile of a four-lane highway. For the highway, one-half mile of each of the two lanes headed north, for example, total one full mile of highway length. Meanwhile, for the two-lane road to reach one mile of length, the northbound lane must extend a full mile, which is twice the distance of the four-lane highway.
Daily vehicle miles of travel: Daily number of miles traveled by all vehicles, including trucks and other types of vehicles.