Abstract: Apparatus is disclosed for monitoring use of a carriageway, the carriageway having two or more lanes (12, 14, 16) for use by vehicles travelling in a single direction A, the apparatus including: a pair of inductive loops (20abc, 22abc) on or in the surface of each lane (12, 14, 16), the loops in the pair being positioned substantially side-by-side across the lane (12, 14, 16) and the pairs of loops (18a, 18b, 18c) being positioned substantially side-by-side across the carriageway, each pair of loops (18abc) substantially extending across the full width of the lane (12, 14, 16), and each loop having a length in the direction of vehicle travel which is substantially shorter than the width of the loop across the lane; a loop controller associated with each loop, each loop controller energising its associated loop and carrying out measurements of the inductance of its associated loop; and processing means for receiving the measurements from the loop controllers, and for using the measurements for calculating the