The unevenness of road surface is an important measure of road condition and a key factor in determining vehicle operating costs. A number of instruments have, therefore, been developed for measuring unevenness, which is usually called roughness and standard roughness scales have been established. However, many of the instruments are expensive and complicated to use or require regular calibration.
Modified Roughness Indicating machine is a simple machine to measure roughness, also called MERLIN - Machine for Evaluating Roughness using low-cost Instrumentation.
The device can be used either for direct measurement or for calibrating other instruments such as the Vehicle Mounted Bump Integrator. The equipment is easy to use, self - calibrating, robust, easily maintained and employs readily available components.
Principle of Operation
The Machine consists of a metal frame 1.8 metres long with a wheel at the front and a metal foot at the rear. Above the rear foot are handles used for moving the machine. Midway between the wheel and the foot is a probe which is attached to a weighted arm to hold it on to the road surface.
At the other end of the arm is a pointer which moves over a prepared chart consisting of a series of 5 mm wide columns. The arm is pivoted close to the probe so that a vertical displacement of the probe of 1 mm produce an equivalent displacement of the pointer by 1 cm of the pointer.
The position of the pointer on the chart hence gives an accurate indication of the position of the probe with respect to an imaginary lines, which joins the bottom of the wheel and rear foot. If the position of the pointer is noted at a number of places along a road, then the rougher the road, the greater the spread of readings. It has been shown that the spread correlates well with road roughness as measured on standard roughness scales.