Before revision: For heavy duty commercial vehicles it is recommended 4-6 seconds following distance for speeds under 30 MPH , and 6-8 seconds following distance for speeds over 30 MPH .
After revision: For heavy duty commercial vehicles it is recommended 4-6 seconds following distance for speeds under 30 mi/h (48 km/h) , and 6-8 seconds following distance for speeds over 30 mi/h (48 km/h) .