Weakness

Strength

Measurement index

Associated standard

Test method

-It cannot be used on Curves, T-sections or Roundabouts.

-It might miss slippery sections.

-Continuous measurement of skid resistance is not possible due to its intermittent performance.

-Its test equipment has high primary and operating costs.

-Determination of speed dependency of skid resistance can only be performed by repeated measurements.

-It contains user friendly

systems with relatively simple and non-time consuming performance.

The Coefficient of friction (μ) is computed by measuring the resistive drag force and the wheel load applied to the pavement.

Friction is reported as friction number (FN) or skid number (SN).

ASTM E 274

Locked-wheel

-It is very sensitive to road potholes, cracks, etc. and these defects can destroy tires quickly.

-Mu-Meter is not a universal test rig and is often used for airports in the U.S.

-Skid condition is like the fixed slip device, relatively well controlled.

-It can be used on straight sections and curves, T-sections or Roundabouts.

-It performs continuous measurement throughout a test pavement section.

The Mu Number, (MuN) or the sideways force coefficient, (SFC) is computed by measuring the average of the side force perpendicular to the plane of rotation.

ASTM E 670

Side-force

-The slip speed of this device especially on snow covered surfaces does not always coincide with the critical slip speed value.

-This device needs large amounts of water for continuous measurement.

-It presents Continuous measurement.

-High resolution friction data can be collected.

It can be used for network and project level friction monitoring.

Coefficient of Friction, (μ) is computed by measuring the resistive drag force and the wheel load applied to the pavement.

the Friction is reported as FN.

Various

Fixed slip

-This test equipment are large and complex

-Maintenance costs of equipment are high.

-Data processing and analysis is complicated.

-Needs large amounts of water for continuous measurement.

-It can present continuous measurement.

-The Rado shape factor can be provided for detailed evaluation.

This test produces the indices below:

-Longitudinal slip friction number

-Peak slip friction number

-Critical slip ratio

-Slip ratio

-Slip to skid friction number

-Estimated friction number

-Rado Shape factor

ASTM E1859

Variable slip

-It only measures a frictional property of surface at a low speed.

-It exhibited unreliable behavior when tested on surfaces with coarse texture.

-BPN has a large variability and operator procedures and wind can have impact on it.

-This test needs traffic control and lane closure.

-It cannot be used for network evaluation because of its spot measurement.

-The British Pendulum skid tester is probably the most widespread skid resistance measurement equipment in the world.

-Can be used for both field and laboratory evaluation.

-This device is highly portable and easy to handle.

The British pendulum tester provides British Pendulum Number (BPN) based on the return height of pendulum, after a low speed sliding contact with the pavement surface.

ASTM E303

British pendulum test