According to Handbook 44, all approaches for any type of NTEP-certified, legal-for-trade truck scales shall be 10′ long, flat, level, the width of the scale and constructed of concrete. The ramps plus the approach must be at least half as long as the scale, but no more than 40′.
A 70′ long scale must have a minimum of 25′ long ramp and the approaches must be 10′ long for a total of 35′. This equates to a total length of 140′ needed for a 70′ long above ground truck scale. Check with local and state regulatory agencies for required approach lengths in your area.