60 mph environmental speed limits. These new 70 mph limits exceeded what is allowable under the environmental speed limit regime. NTTA was allowed to raise the speed limits by offsetting the higher limits' theoretical emissions increases with other transportation-related emissions reduction measures, including implementation of all-electronic tolling, which eliminated the need for some vehicles to stop at a toll booth. In 2015, the Texas Department of Transportation cancelled all remaining environmental speed limits in the Dallas-Fort Worth region. Some speed limits were changed back to those in place before the environmental speed limits were enacted. On some roads the speed limit was not changed. On other roads, including some that never had environmental speed limits, speed limits were raised higher than they were before the environmental speed limits were enacted. 75 mph limits Because Texas law allows speed limits on any numbered state highway, city maintained road, or tollway, it is the only state with 75 mph limits on two-lane roads. Speed studies undertaken by TxDOT in response to legislation passed in 2011 took about 2 years, and the result is that the mileage of highway with a speed limit of 75 mph has increased from about 1,400 to about 19,000. 70 mph or lower speed limits have become unusual on rural Texas roads. Also, there are multiple urban Interstates and tollways in Texas where there is a 75 mph speed limit, such as I-20 in Odessa and Midland (prior to February 2016; it is now 65 mph on I-20 in Odessa-Midland), I-10 in the outer parts of San Antonio, and several managed toll lanes in the DFW area. 80 and 85 mph limits Texas statutorily allows speed limits on I-10 and I-20 in certain counties named in the statute, each of which has a low population density. Separately, the Texas Transportation Commission may set a speed limit up to on any part of the state highway system if that part is "designed to accommodate travel at that established speed or a higher speed" and an "engineering and traffic investigation" determines the speed is "reasonable and safe". As of now, the roads with an 80 mph limit are: I-10 between mile 61.8 in Hudspeth County () and mile 494 in Kerr County () I-20 between mile 0 in Reeves County () and mile 89 in Ward County (). State Highway 45 South from the northern junction with US 183 to