METHODST3

DE"fERMINATION OF THE LONGITUDINAL REGULARITY OF A ROAD SURFACE BY MEANS OF A ROLLING

STRAIGHT-EDGE

1 SCOPE The method describes the determination of the longitudinal regularity of a road surface by means 01 a rolling straight-edge,

2 APPARATUS 2. i A rolling straight-edge consisting of a frame 3,05 m in length carried on 40 fixed

wheels. each 127 mm in diameter. The wheels must be fitted in two paraliel rows, 114 mm apart. The wheels in each row must be 152 mm, centre to centre, arranged in such a manner that the centre of each wheel is opposite the space between two wheels in the other row. In the middle of the frame and centrally between the two rows of fixed wheels a measuring wheel must be fitted on an assembly that can move freely up and down when the straight-edge is pushed over an uneven surface. The vertical movement of the measuring whee! must be registered on a dial gauge which should be readable at a distance of 2 m. The measuring wheel must also drive a suitable distance meter readable at 2 m and the measuring wheel must be fitted with an electric beH that can be adjusted to ring when a specified maxi mum deviation in surtace regularity is exceeded (see 5.1). A handle. 2 m in length, must be fitted to the instrument for pushing it. The frame of the rolling straight-edge normally consists of three sections which can be disassembled in order to facilitate handling and transport when not in use. When the instrument is assembled, care must be taken to ensure that the sections fit properly to-gether and that there is no horizontal or vertical movement between them.

2.2 A calibration board consisting of a suitable wooden plank 3 150 mm long and 200 mm wide with a specially prepared flat surtace and a groove 3 mm deep and 150 mm wide across the middle of the board (see Figure ST3i l).

3 METHOD 3.1 Calibration

Before each day's measurements are taken. the rolling straight-edge should be calibrated as follows: Move the straight-edge onto the calibration board so that the measuring wheel rests in the 3 mm groove. Record the reading and move the straight-edge so that the measuring wheel is out of the groove and on the surtace of the board. Record the reading. Adjust the instrument so that a zero reading is obtained when the measuring wheel is on top of the board and 3 mm when it is in the groove.

3.2 Measurement on the road Position the rolling straight-edge parallel to the centre line of the road. This is normalfy in a wheel path 1 m from the outer or i m from the inner demarcation

Special methods Draft TMrl6. Pretoria, South Africa, 1984 11

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line of the lane that must be measured (see 5.2). Zero the distance meter and adjust the bell mechanism to ring when the required maximum deviation is ex-ceeded. Switch on the electric bell mechanism and push the rolling straight-edge forward at a walking pace (approximately 1 to 2 km/h) and parallel to the centre line. Note the number of deviations greater than the specified maximum as well as the maximum deviation obtained. The road is normally sub-divided into short sections of 100m each and the results of each section are recorded separately,

4 CALCULATIONS Calculate the average number of deviations from the specified maximum for the whole section measured as follows:

d X ... -

n

where X "" average number of deviations for the number of 1 00 m sections in a par-

ticular whee!path d ;;; sum of deviations for the number of 100 m sections measured n =: number of 100 m sections measured. The maximum deviation for each wheelpath must also be recorded. The results should be recorded on a suitable data sheet

5 NOTES 5.1 The maximum deviation that can be measured with the roiling straight-edge IS

12mm. 5.2 The operator must ensure that the area of road to be tested has been cleared

of loose stones, dirt or anything else that may influence the readings.

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REFERENCE YOUNG, J C. Calibration, maintenance and use of the Rolling Sfraight-edge. TRRL Supplementary Report 290, UK Transport and Road Research Lab-oratory, 1977.

Special methods Draft TMH6, Pretoria. South Africa. 1964

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