The existing measurement technique uses three coaxial cables which are fixed to the road surface in a reverse “Z” type formation. When a tyre runs over a cable, a triboelectric effect produces electron migration in the cable. The charge from the electron migration can be amplified and converted to a voltage pulse. Timings of voltage pulses can be analysed and used to produce a lateral position and code for each passing vehicle. Limitations with the “Z” measurement technique mean that position data is only available for the right hand side of the vehicles tyres. As no information on tyre width or type is collected, exact wheel paths positions cannot be calculated.

To try and overcome these limitations, an additional diagonal cable was introduced in order to capture the left hand side position of each tyre (or pair of tyres). Comparisons, between left and right hand side tyre positions, could then be carried out to produce tyre width values.