Maine raises the bar to 75 mph on one stretch of I-95.
Posted speed limits are something that drivers routinely flout, especially on isolated open roads where traffic is light, enforcement is minimal or non-existent and when time is a factor. Beginning in the mid-1970s, the federal government legally limited highway speeds to 55 mph, setting a ridiculously low threshold that was ignored with abandon.
Federal laws were loosened in 1987 and completely done away with in 1995, returning speed limit jurisdiction back to where it belongs: the states. Today, all 50 states feature posted speed limits above 55 mph with some stretches of roads in Texas allowing 85 mph.
East of the Mississippi River, speed limits above 70 mph have not been found, but starting this month the state of Maine is raising the bar to 75 mph, at least on one section of highway.  A 100-mile stretch of I-95 from Old Town to Houlton has had its speed limit raised from 65 mph to the higher limit, reflecting the driving habits of Mainers. That section of the highway is in the far northern area of the Pine Street state, just shy of the New Brunswick, Canada, border.
Posted Speed Limits
Speed limits across the United States vary depending on the road you’re on and location. Typically, states mandate 25 mph near schools and hospitals, incrementally raising speeds above 35 mph away from congested areas. In the northeast, highways in urban areas most often have 55 mph limits, with top speeds of 60 to 70 mph on interstates.
Higher speed limits can be found west of the Mississippi, with many states allowing drivers to go 75 mph. In Utah, portions of I-15 allow drivers to travel at 80 mph. In Texas, a top speed of 85 mph is allowed on certain remote roads with rural sections of I-10 and I-20 permitting speeds of 80 mph. 
Lower Speed Limits
Some states with wide open expanses of highway still restrict drivers to 65 mph. Besides those in the northeast, Illinois and Wisconsin have posted limits of 65 mph. Alaska, the most remote state of all, also limits your top speed to 65 mph. Hawaii, with minimal stretches of open road, has a state speed limit of 60 mph, the lowest in the nation.
Posted speed limits are simply a guide and drivers can go below these limits by staying in the right lane and allowing others to pass. Weather is a factor too – adjust your speed accordingly whenever visibility and road conditions change. Lastly, if your tires are not up to the task, then keep your speeds down. Aged or worn tires should be replaced regardless of your speed and personal driving habits.
See Also — Back to School Driver Safety Tips