Speed limits have increased on sections of Interstate 40 and Interstate 640 in Knox County, Tenn. Additionally, split speed limits have been eliminated.

According to the Tennessee Department of Transportation, the following speed limits have changed:

I-40 from mile marker 367.8 (between the I-40/I-75 split at Watt Road) and mile marker 385.2 (near the I-40/I-640 split) goes from 65/55 mph or 55 mph, to 65 mph throughout.

I-40 from mile marker 385.2 to mile marker 390.2 (near Cherry Street exit) goes from 55 mph to 60 mph.

I-40 from mile marker 385.2 to mile marker 390.2 (near Cherry Street exit) goes from 55 mph to 60 mph. I-40 from mile marker 390.2 to mile marker 395.7 (between Asheville Highway exit and Strawberry Plains exits) goes from 65/55 mph to 65 mph speed limit throughout.

I-40 from mile marker 395.7 to mile marker 409.7 (past the Sevierville exit) goes from 65/55 mph or 70 mph, to 70 mph throughout.

I-640 from mile marker 0.0 (at the I-40 split) to mile marker 3.6 goes from 55 mph to 65 mph.

I-640 from mile marker 3.6 to 10.6 (at the I-40 split) goes from 55 mph to 65 mph.

TDOT spokesman Mark Nagi told Land Line that the department began reducing speed limits to improve air quality in 2004. As a result, speeds were reduced from 70 mph to a split 65/55 mph in the Knoxville area.

Several years later, the area has obtained full compliance with the current National Ambient Air Quality Standards, according to TDOT. Consequently, the department reviewed posted speed limits in the Knoxville area.

TDOT found that 87% to 98% of motorists were already going over the 55 mph speed limit.

The Manual on Uniform Traffic Control Devices advises posted speeds to be within 5 mph of the 85th percentile speed. In this case, that speed is between 67-75 mph, regardless of the speeds posted.

“In some spots, over 25% of all traffic was traveling above that critical speed (15 mph over limit),” Nagi said. “According to crash data, with the exception of a part of I-40 in downtown Knoxville, crash rates are below the statewide average in the study area.”

Signs reflecting the updated speeds have been installed in affected areas.