Road Transport Act 2013

The average speed limit for a driver of a vehicle on a road between detection points in circumstances where more than one speed limit applied to the driver between those points is to be calculated in accordance with the following formula (and expressed in kilometres per hour rounded up to the next whole number)—

where—

D_T is the total shortest practicable distance (expressed in kilometres and rounded down to 2 decimal places) that could be travelled by the vehicle on a road between the detection points.

D₁, D₂…D_n are each part of the total shortest practicable distance D_T between the detection points (expressed in kilometres and rounded down to 2 decimal places) for the different speed limits S₁, S₂… S_n that would have applied to a driver of the vehicle between the detection points.

S₁, S₂…S_n are each of the speed limits (expressed in kilometres per hour) that would have applied to a driver of the vehicle if the vehicle were travelling along the shortest practicable distance D_T on a road between the detection points.