The highest speed limit in the United States is 85 mph, posted on a 41-mile stretch of Texas State Highway 130 running between Mustang Ridge and Seguin, southeast of Austin. That corridor has held the national record since 2012, and as of March 2026 no state has authorized anything faster. The next tier down is 80 mph, allowed on designated highways in eight states.
The 85 MPH Stretch in Texas
The 85 mph zone covers segments five and six of State Highway 130, a toll road that runs roughly parallel to Interstate 35 through central Texas. It was built to pull long-distance traffic away from the congested I-35 corridor, and the surrounding landscape is largely open and undeveloped.1United States Department of Transportation. SH 130 Segments 5-6 Austin TX
The Texas Department of Transportation set the 85 mph limit in September 2012 after an engineering study confirmed the road’s design could handle it. Setting the limit that high triggered a $100 million increase in the concession fee owed by the private developer that built and operates the road under a 50-year agreement with the state.1United States Department of Transportation. SH 130 Segments 5-6 Austin TX
No other public road in the country is posted at 85. If you want to drive at the legal maximum in the U.S., this stretch is the only place to do it.
States That Allow 80 MPH
Eight states let passenger vehicles travel at 80 mph on designated highway segments as of March 2026:
- Idaho, on specified segments of rural and urban interstates
- Montana, on rural interstates
- Nevada, on rural interstates
- North Dakota, on rural interstates (effective August 2025)
- Oklahoma, on specified turnpike segments
- South Dakota, on both rural and urban interstates
- Utah, on specified segments of rural interstates
- Wyoming, on specified segments of rural and urban interstates
In most of these states, the 80 mph limit applies only after a traffic engineering study confirms a given stretch can handle it. Idaho, Oklahoma, Utah, and Wyoming all require that study before raising limits above the default. North Dakota is the most recent addition, signing its 80 mph law in 2025 to join neighbors South Dakota and Montana. South Dakota is the outlier for posting 80 mph on urban interstates; most other states reserve the number for rural corridors with long sightlines and low traffic density.2Insurance Institute for Highway Safety. Maximum Posted Speed Limits
Truck Limits Are Often Lower
Every number above applies to passenger vehicles. If you’re driving a commercial truck or towing a heavy trailer, the legal maximum is frequently lower, and the posted sign may only show the passenger limit. A few of the sharper splits as of March 2026:
- California: passenger vehicles 70 mph on rural interstates, trucks capped at 55 mph statewide
- Montana: passenger vehicles 80 mph on rural interstates, trucks limited to 70 mph
- Michigan: passenger vehicles 75 mph on designated segments, trucks capped at 65 mph
- Washington: passenger vehicles 70 to 75 mph, large trucks capped at 60 mph
- Indiana: passenger vehicles 70 mph, trucks limited to 65 mph
Not every state splits the limit this way. In many, the same number applies to everyone.2Insurance Institute for Highway Safety. Maximum Posted Speed Limits
Why States Can Post Numbers This High
In 1995, Congress passed the National Highway System Designation Act, which repealed federal control over speed limits and returned that authority entirely to the states.3Congress.gov. S.440 – National Highway System Designation Act of 1995
Before that, the federal government had dictated maximum highway speeds for over two decades. The Emergency Highway Energy Conservation Act of 1974 imposed a national 55 mph limit during the oil crisis, and in 1987 Congress loosened the cap to allow 65 mph on rural interstates. States that posted higher risked losing federal highway funding. The 1995 repeal eliminated that leverage, and within months states began raising limits. The 85 mph in Texas, the 80 mph across eight states, and the 75 mph limits in a dozen more are direct products of that shift.
How Engineers Justify a Number That High
The standard tool is the 85th percentile speed, the speed at or below which 85 percent of drivers naturally travel on a given road when no enforcement is visible. Engineers measure it with sensors or radar recording actual traffic.4Federal Highway Administration. Speed Information The logic is that most drivers pick a speed that feels safe for the road, and posting a limit far below that natural speed widens the gap between the fastest and slowest cars, which tends to produce more crashes than the higher number would.
The Federal Highway Administration’s speed limit setting guidelines say the 85th percentile speed should not be the sole factor. Engineers are supposed to weigh at least five other considerations: the roadside environment and land use, physical road characteristics like lane width and sight distance, geographic context, crash history from at least 12 months of data, and any past speed studies that reveal trends. For freeways and rural highways outside developed areas, the FHWA recommends posting a limit within 5 mph of the 85th percentile speed, provided all six factors have been evaluated and none of them suggest a lower number.5Federal Highway Administration. Speed Limit Setting Handbook
That framework is how Texas justified 85 mph on SH 130. The road was designed from scratch to handle those speeds, the surroundings are undeveloped, and the engineering study confirmed drivers were already traveling in that range.5Federal Highway Administration. Speed Limit Setting Handbook