<P> Speed limit drops generally are done in 10 mph increments but 20 mph are not uncommon . Improvements in the mid-2000s were done by SCDOT to warn motorists ahead of time for speed drops on various roadways . However, there are still some roadways that have not received that treatment . However, there are a couple roadways that get 25 mph to 30 mph drops as well . The speed limit drops from 55 mph to 25 mph at a traffic circle with US 378 and SC 391 in eastern Saluda County . On US 52 northbound approaching Kingstree, the speed limit drops from 60 mph to 35 mph </P> <P> Shortly after the December 1995 repeal of the 65 / 55 mph National Maximum Speed Law, South Dakota raised its general rural speed limits to 75 mph on freeways and 65 mph on other roads along with 70 on a few 4 lane divided highways . Almost a decade after posting the 75 mph limit, average speeds on South Dakotan rural freeways remain at or below the speed limit . In the urban areas of Sioux Falls and Rapid city, a 65 mph speed limit is posted on Interstates 90 and 29 . In March 2015, SD State Legislature has passed the bill to raise the speed limit on Interstate 29 and Interstate 90 to 80 mph . It was signed into law and took effect in April 2015 . While the 80 MPH speed limit was initially signed on all rural freeways in the state, the Interstate 90 stretch from Rapid City to the Wyoming Border returned to 75 mph due to safety concerns . </P> <P> Tennessee generally posts its rural interstates at 70 mph . These include all of the state's two - digit Interstates except Interstate 55 and Interstate 26 . The only auxiliary interstates in Tennessee with a 70 mph speed limit are Interstate 155 and Interstate 840 . 70 mph speed limits are allowed on all other controlled access highways, and are found on controlled - access portions of U.S. 51 and S.R. 22, 111, 386, and 396 . In 70 mph zones, the default minimum speed limit is 55 . Urban interstates are generally posted at 55 to 65 mph, however, portions of Interstates 24, 40, and 65 and S.R. 386 in Davidson County, as well as I - 24 in Clarksville are posted at 70 mph . Four - lane divided highways are posted as high as 65 mph but are sometimes 55 mph . These are often hotbeds for speed camera enforcement leading into a municipality. 55 mph speed limits are allowed on two - lane state maintained roads, but some contain 45 and 50 mph limits, even in rural areas, primarily as a result of local policies . In East Tennessee, most mountain roads leading to North Carolina are poorly posted at 45 mph . Furthermore, two - lane roads such as US 321 and S.R. 91 have the same mountain and road width characteristics when leaving Tennessee into North Carolina or Virginia at 55 mph . </P> <P> Inside a municipality, speed limit assignments are often a mystery on state - maintained roads . This could range from 15 to 55 mph depending on the type of roadway . This is because the state of Tennessee grants strong home rule powers to municipalities and Dillon's Rule for unincorporated areas in the county for speed limit assignments on non-controlled access state - maintained roads, requiring that they fall within established constraints . Unlike other states, this weakens TennDOT's ability to sign predictable speed limits in a reasonable and prudent matter . Also, Tennessee has a high percentage of roadways maintained by the counties . </P>

What is the speed limit on i 40 in tennessee
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