The system carries out continuous in-vehicle data measurement and storage for subsequent processing. A given driving manoeuvre is sub-divided into facets and the measured vehicle data is processed to provide a local rating for each of the facets using empirically derived transfer functions. The local ratings are weighted and combined to provide an overall rating which is converted to a rating out of ten based on a further transfer function based on correlations between derived and subjectively observed ratings. As a result, driveability rating and engine calibration/development can be accelerated and targeted.