The four lasers within the HRM provide data on the longitudinal profile and
macrotexture of the pavement. In addition, a laser mounted at the mid-point of
the trailer axle is used along with the trailer wheels to measure the average rut
depth in the nearside and offside wheelpaths. Inclinometers mounted on the
trailer estimate the crossfall and gradient on the highway. Horizontal radius of
curvature can also be estimated. A device fitted to the nearside trailer wheel provides distance information to which all HRM measurements are referenced