Texas is unique in a number of ways. It is one of only two states that was ever its own country, Hawaii being the other one. It is unusual for having its own power grid. And the state of Texas has a number of quirks when it comes to its highway infrastructure, many of which are literally by design.
Unusually High Overpasses
Many highway interchanges rely on overpasses to allow one road to literally pass over another. However, one of the quirks of Dallas highway engineering is how tall these overpasses may be relative to others, both elsewhere in the state and around the country. The highest point on the I-635 / US I-75 interchange is 117 feet off the ground. The other bridges in the 635-75 interchange in Dallas are also very high. That explains why the entire I-635 / US I-75 interchange is nicknamed “The High Five”. Fort Worth has its own variation of this in the I-35 West / I-30 “Mixmaster”. The highest overpass in that interchange is 110 feet tall. We can say that Dallas highway engineering results in some of the highest cloverleaf loops in the country.
Yet tall overpasses are not limited to Dallas-Fort Worth. There are highway overpasses in Houston that approach 100 feet in height, such as the one connecting I-45 and Texas Highway 130. This is partially due to the Texas-style stack, where there are four and five overpasses and underpasses in the same highway interchange. Houston is notable for the sheer number of these interchanges, leading to the city getting the nickname “Stack City”.
These multi-level overpasses and underpasses are installed to minimize the number of roadway conflicts. This is a necessity, because Texas unlike nearly every other interstate highway system in the country, has frontage roads. These frontage roads, also known as service roads or feeder roads, allow people to travel parallel to the highway without getting on it. One point in favor of this is that businesses can line up along the highway and profit from a steady stream of visitors instead of having to exit the highway and take a mile of side streets to reach restaurants and hotels. This increases the economic benefit that comes from interstate and intrastate travel. One side benefit is that people experiencing car problems can get off the highway and stop almost anywhere. Another point in their favor is that people can exit early from the highway and continue slowly on the frontage road, looking for the side street they want. There are fewer people in the left lane cutting across traffic because they realize they’re about to pass their exit.
On the flipside, the existence of frontage roads adds a fifth level to the interchanges, because the access roads need to join with and cross over the two major highways connected via the interchange. The sheer height of these interchanges is due to the rules that say every level of the interchange must have at least 25 feet of clearance. This is how Texas having frontage roads affects Dallas highway engineering.
The Regular Use of Frontage Roads
Every highway has two or more lanes, and they’re generally required to have shoulders. Texas is unusual for having frontage roads along nearly every major highway and many mid-sized ones. Frontage roads were the brainchild of Dewitt Greer. He was the Texas chief highway engineer from 1940 to 1968. He initially considered frontage roads to be a great way to reduce right-of-way acquisition costs. Buy the land for the highway and an additional 20 feet or more on each side for frontage roads. This allowed the state to buy up wide swaths of land for the interstates. More importantly, there was ample room on each side of the highway if the highway needed to be widened.
This made it easy to expand I-635 in Dallas from 6 lanes to 8 or 10, if you want to include the HOV lanes. There was no need to fight to buy up houses backing up to the highway in order to widen it. In the worst case scenario, the Texas Department of Transportation sacrificed the frontage road to widen the highway. In most cases, the frontage road went from two lanes to just one. Dallas highway engineering projects often resulted in frontage roads shut down one way or the other while I-30 or Loop 635 were widened or renovated.
Another benefit of having frontage roads is that it gives everyone from first-responders to tow trucks to construction vehicles greater access to the highway. An ambulance can take the frontage road if the highway is blocked. A point in favor of frontage roads is that people can get off a highway blocked by an accident and get on the frontage road. Blocking emergency vehicles is a felony in Texas and you would have to hire a criminal attorney Dallas TX. So frontage roads reduce criminal negligence. They might have to drive over dirt and grass to get there, but this does end up alleviating massive traffic jams. Frontage roads also separate local traffic from through-traffic. When people don’t need to get on the highway to travel a few miles, this tends to reduce congestion and speed up traffic on the highways.
What are the downsides of frontage roads? They increase the initial construction costs. They provide ample space for highway signage, and some consider this an eye-sore. In a surprising number of cases, the frontage roads contributed to worsening traffic instead of relieving it. The fact that you could easily take advantage of commuter traffic led to stores building right along the frontage road. This leads to more people getting on and off the frontage road, whether they’re going to the grocery store, hitting a restaurant or pulling into a mall. This often results in traffic jams on the frontage road that indirectly leads to a pile up on the highway, since people on the highway need to get onto or across the frontage road to get where they’re going.
That’s why there was a proposal in 2001 to limit construction of new frontage roads. Dallas Mayor Ron Kirk rejected that proposal, stating that frontage roads were essential to the economy of impoverished south Dallas neighborhoods. The Texas Transportation Commission relented to Mayor Kirk’s pleas, and new frontage road construction was authorized. It has continued ever since. And that is how Dallas highway engineering affects road engineering across the entire state.
Another issue with frontage roads is that it increases the width and risk that crossing them poses to pedestrians. And very few Texas cities have built pedestrian bridges over highways. There might be a gap of miles between crossing bridges. That results in highways literally cutting off parts of the community from those on the other side if the highway. For example, Dallas highway engineering significantly impacts sections of the city south of I-20, hence the calls to maintain frontage roads.
Some people are concerned that frontage roads contribute to urban sprawl. It makes the land next to the highway valuable, and it drives development of the land along the highway even when it is several miles from downtown. Once there are restaurants and hotels, general retail and commercial construction follows. The impact is so great that population density along Texas highways is several times that of the rest of the state. And rural communities along highways like I-35 are growing while other rural communities are depopulating.
Ironically, the very existence of frontage roads from the Mexican to the Oklahoman border was that Texas could propose the Trans-Texas Corridor. This project was nicknamed the NAFTA Superhighway. This could only happen because Texas had enough land to seriously consider building a second toll-road highway parallel to I-35. It would have been called TTC-35. It would probably look like the Katy Freeway. That name refers to a section of Interstate 10 west of Houston. It is up to 26 lanes wide if you include the frontage roads. This is where Houston exceeds otherwise impressive Dallas highway engineering.
The I-35 Split
Interstate 35 is a true international highway. It stretches from the Mexican border to the Canadian border. Furthermore, it is a wide highway the entire way. Cities competed for the interstate highway the way they used to compete for a rail-line to pass through. And they did so for the exact same reason – accessibility and the associated economic benefits.
When the interstate system was being planned, the question arose: Does it pass through Dallas or Fort Worth? The answer was: both. Interstate Highway 35 splits into I-35 East and I-35 West in Hillsboro, Texas. Each highway segment runs north for nearly 100 miles. They merge again in Denton, Texas, more than thirty miles north of Dallas. We can consider it a hallmark of Dallas highway engineering, since the interchange is only an hour drive north of Dallas.
Note that this is very different from Interstate 20 and Interstate 30 merging west of Fort Worth near Weatherford, Texas. In that case, two interstate highways merge into a single highway, I-20. The I-35 split is also significantly different from the rather common practice of having a “business highway-number” road branch off from the highway, though it may merge back into the highway at another point. The practice of having a “business highway-number” road can be seen as the way to give people on the highway access to the amenities in a given town. Texas mostly eliminated the need for this solution with its extensive frontage road system, though you can find “business 121” or “business 114” in addition to state highways with those same names.
The Sheer Number of Toll Roads
Texas has more toll roads than any other state. Toll roads have been used to fund road construction that otherwise wouldn’t happen due to the state’s low tax rate. Toll road construction and operation are generally overseen by regional mobility authorities or RMA. For example, the State Highway 121 and State Highway 114 express lanes are managed by the North Texas Tollway Authority. These express lanes add one to two new lanes on existing highways. People pay for the privilege to travel on them instead of the more congested state highways. The NTTA manages a number of toll roads in the Dallas-Fort Worth area, notably the Dallas North Tollway and President George Bush Turnpike that passes through the northern Dallas suburbs. This makes toll roads a hallmark of Dallas highway engineering.
There are privately managed toll roads in Texas, as well. For example, Dallas/Fort Worth International Airport operates its main access road, International Parkway, as a toll road. Sections of State Highway 130 are a privately managed toll road, too.
Texas likes to fund new infrastructure through toll roads, since the cost of building and maintaining the road is paid only by those who use it. This is why there are numerous toll bridges across Texas. For example, you can find toll bridges across Lewisville Lake and Mountain Creek Lake. You can even take a toll tunnel to Addison Airport. That bridge extends Keller Springs Road under the airport. Note that Addison is a suburb of Dallas, making the toll tunnel a unique feature of Dallas highway engineering.
Roads as Boundary Markers
Texas is already strange for allowing smaller cities to reject annexation by a larger city if they share a boundary with a third city. This is why there are literally cities within cities in Texas. For example, Highland Park and University Park were once north Dallas suburbs. As the city of Dallas stretched north, these two cities decided to reject annexation by Dallas and could refuse to be annexed because they touched each other. The same phenomenon is seen inside of Arlington, a Fort Worth suburb. Pantego and Dalworthington Gardens share a border, so they were able to refuse annexation by Arlington.
All of this remains true after Texas revised its annexation laws in 2019. That rule change dealt with the tendency of cities to annex Dallas highways and freeways. They often did this in order to be able to make money off traffic tickets given to people traveling on the highway. In other cases, they annexed just a few hundred feet past the edge of the highway, so that they could claim the property and sales taxes on property along the frontage roads. Yet they rarely went more than a few hundred feet past the highway, leaving entire suburban subdivisions unincorporated.
The revised rules state that the city cannot annex property without permission of the property owner, and they can’t annex property along the highway unless it actually borders the city limits. This prevents cities from counting 6 lanes of a highway as part of the city and then annexing the mall ten miles north of town. And if the city border ends at the highway, properties on the other side of the highway cannot be annexed unless the city annexes the roadway, as well. A city cannot annex a road or right-of-way unless the governing body controlling the road allows it. For example, a city couldn’t annex a toll road and the buildings on the other side of it without permission from an organization like the NTTA. For county roads, that permission has to come from the county commissioners.
As the second largest state, it isn’t surprising that Texas has the largest number and mileage of roads. However, the state has a number of unusual rules and precedents that literally shape its highway infrastructure and affect its political landscape.