Rolling straight-edge

The rolling straight-edge was developed by the British Road Research Laboratory to replace earlier manual methods of measurement using rulers.

[4] As an example of a unit the Road Research Laboratory rolling straight-edge measures 3 metres (9.8 ft) in length with the sensor mounted at the midpoint.

[4][6] This method had later been developed by the British Department of Transport with the use of graduated wedges which were pushed under the ruler to measure the height, but remained a slow and cumbersome technique.

[4] The current British practice as set out in its national standards, the Specification for Highway Works, is for the rolling straight-edge to be used for checking surface regularity of all sections of road longer than 75 metres (246 ft) in length.

[10][11] The National Academies of Sciences, Engineering, and Medicine's journal Transportation Research Record in 1996 described the instruments as "cumbersome devices with limited production capability" and noted that they could miss deviations with a wavelength of half the length of the straight-edge, due to the fixed points of reference at either end.

[10] By 2001 36 US state departments of transport were specifying the use of profilographs to derive a profile index as a measure of surface regularity, rather than rolling straight-edges.

[13] The Taiwan Area National Expressway Engineering Bureau specification requires a rolling straight-edge as a means of measuring surface regularity.