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Technical

All data is collected by the SCRIM+ vehicle, in a single pass, at a survey speed of up to 60km/hr.

Transverse Profiles

The transverse profile bar uses 20 lasers to define the transverse profile over a width of 3.3 metres. The rut depth in each wheelpath is calculated from the transverse profile using a simulated 2 metre straight edge. This data is used to determine the average, maximum minimum rut depth, the standard deviation and the distribution of rut depths. This is reported every 20 metres.

Longitudinal Profile (roughness)

The longitudinal profile is measured using two lasers, one in each wheelpath, together with accelometers fitted on the transverse beam. Vehicle suspension effects are defined by the accelerometers and deducted from the laser output to provide the road profile. The International Roughness Index (IRI) is calculated from the longitudinal profile using the World Bank Quarter Car model, and is reported every 20 metres.

Texture

Texture is measured by three 32kHz lasers, one in the left and right wheelpath and one in between the wheelpaths. Accelerometers remove most of the vehicle motion relative to the road to provide a stable inertial profile from which the MPD (Mean Profile Depth) is calculated. The MPD is measured and calculated according to the International Standard Organisation ISO 13473-1:1997.

Characterization of pavement texture using surface profiles -

Part 1: Determination of mean profile depth. The raw MPD is calculated from the road profiles every 100 mm, but the MPD is reported at the same averaging distance as skid resistance for RAMM.

Geometry

The geometry measurement system used on SCRIM+ utilises inclinometers and
gyroscopes to sense the vehicle attitude as it travels along the road. Inclinometers measure the forward or back tilt of the vehicle for gradient and the side to side tilt of the axles for crossfall. Gyroscopes are used to sense the movement of the SCRIM+ around corners and bends to calculate the horizontal and vertical curvature. Geometry data is smoothed with a 30m moving average and reported at every 10m.

GPS

The SCRIM+ is fitted with Trimble GPS equipment sampling the Omni-Star satellite to record the differential GPS coordinates of the centreline. Tilt sensors for crossfall and gradient together with a gyroscope provide alignment details when out of sight of satellites.

SCRIM

Test wheels are available, mounted mid-vehicle, in both wheelpaths at an angle of 20 degrees to the direction of travel. The test wheel, which has a smooth pneumatic tyre of standard hardness, is freely rotating and is applied to the road surface under a known load. A controlled flow of water wets the road surface immediately in front of the test wheel. When the vehicle moves forward, the test wheel slides in a forward direction on a wet road surface. The force generated by the resistance to skidding is related to the wet skidding resistance of the road surface. Measurement of this sideways component allows the sideway force coefficient to be calculated as an average for each continuous 10m section.