Heads up, drivers – by early summer the Tennessee Department
of Transportation will reduce the speed limit for all vehicles traveling on
urban interstates in Shelby County as part of an effort to clean the air.
Currently, all vehicles are allowed to drive 70 mph.
Gerald Nicely, Tennessee’s transportation director,
announced the authorization for posting 55-mph speed limit signs for large
trucks in the county at a press conference March 14 in Memphis, which is part
of Shelby County. All other vehicles would have new limits of 65 mph.
About 107 miles of interstate will be affected by the speed
limit changes in the county. A section of state Route 385 that runs about 17
miles will also have lower speeds posted.
“After studying the issue we believe that lowering the speed
limit for large trucks will make a difference in air quality for Shelby
County,” Nicely said. “A study conducted by the Federal Highway Administration
shows that reducing truck speed limits by 10 mph can reduce the nitrogen oxide
emission factor by approximately 18 percent or more per truck. If we get
reductions anywhere close to that level in Hamilton County, it will be worth
Nicely said the reason for also reducing the car speed is “to lessen the difference between the rates at which the two types of vehicles
will be traveling.”
Shelby County Mayor AC Wharton requested the lower limit in
a letter sent to Nicely last summer. The Tennessee Air Pollution Control Board
and Metropolitan Planning Organization backed the change.
Shelby is the second county state officials have sanctioned
lower limits for air-quality purposes. Nicely made a similar announcement last
month affecting about 57 miles of interstate in Hamilton County, which includes
the city of Chattanooga.
Davidson County, which includes Nashville, and Knox County,
which includes Knoxville, also have requested speed-limit reductions.
Officials in the state’s largest cities hope the slower
traffic will help their areas meet new federal air-quality standards for ozone
All of Tennessee’s largest metropolitan areas failed last
year to meet the new air standards. Failure to develop plans to clean up the
air by 2007 could result in an end to industrial expansion and large cuts in
federal highway funding for the area.
The speed limit change does not require state legislative