in NC is if determined to be "safe and reasonable" by NCDOT engineering studies. This generally applies to non-freeway primary and secondary roads throughout the state. Prior to the National Maximum Speed Law that went into effect nationwide, North Carolina used to have 60 mph speed limits on two-lane primary and secondary roads. Warning signs are posted in all cases where the speed limit drops on a road. In addition, a "reduce speed ahead" sign is commonly posted on major highways, though it is being phased out. It is rare that NCDOT will assign a speed drop greater than 20 mph. In Bertie County, the US 17 bypass in Windsor drops from 70 mph to 45 mph. In Moore County, Shady Lane Road outside of Carthage in the Hillcrest community drops from 55 mph to 30 mph. In Ocracoke, the speed limit on NC 12 southbound drops from 55 mph to 20 mph. Although not statutory, it is relatively common to encounter speed limits. Many suburban 2- and 4-lane roads, as well as most 4-lane roads within municipal limits, carry a 45 mph speed limit. 45 mph speed limits are also not uncommon in more densely populated rural areas. Subdivision and residential streets generally, though not always carry a speed limit. However, when signs are not present, the speed limit is still 35 mph by default. In downtown areas, it's common to encounter 20 mph speed limits, although those are not statutory at the state level, and are typically controlled by the municipality the area is within. These speed limits are generally considered to be grandfathered in, per a policy from NCDOT stating new speed limits below 25 mph "will generally not be approved." Many arterial roads near the city limits are posted at , but otherwise 50 mph is not commonly posted. There is one interstate posted at 50 mph, I-277 in downtown Charlotte. This is the lowest speed limit on any interstate in North Carolina. School zone speed limits generally entail a 10 to 20 mph reduction below the original speed limit during times of day used for school arrivals and departures. Such a speed limit would be indicated when entering the school zone. Also, the default or modified speed limit is indicated after leaving the school zone. A school zone speed limit cannot be less than 20 mph. Military bases are generally posted at a maximum of