The clearances in Texas are taller than ones I've seen in other states. The national standard is 17 feet, but Texas often uses 18 feet (5.4 meters) or more. Bridges on the East coast interstates sometimes don't even make 17 feet (they often predate many standards).
The theories I've heard as to why TXDOT does this include: they wanted sufficient clearance for mobile oil drilling rigs, military vehicles[0], "just in case", and of course, bragging rights.
You can zoom in and click on the blue dots to see clearances on major TXDOT bridges here:
[0] The US interstate system wasn't really planned for use by the Department of Defense in time of war, but the bill was named "National System of Interstate and Defense Highways" to help it get passed in Congress. This isn't to say that during a national emergency, the highways couldn't be cleared of civilian traffic.
The theories I've heard as to why TXDOT does this include: they wanted sufficient clearance for mobile oil drilling rigs, military vehicles[0], "just in case", and of course, bragging rights.
You can zoom in and click on the blue dots to see clearances on major TXDOT bridges here:
https://gis-txdot.opendata.arcgis.com/datasets/0126e7969bfb4...
[0] The US interstate system wasn't really planned for use by the Department of Defense in time of war, but the bill was named "National System of Interstate and Defense Highways" to help it get passed in Congress. This isn't to say that during a national emergency, the highways couldn't be cleared of civilian traffic.
https://highways.dot.gov/highway-history/interstate-system/5...