Measures of vehicle operations that may be an appropriate basis for consistency rating
methods include speed variance, lateral placement (mean and variance), erratic maneuvers, and
traffic conflicts. These measures have been evaluated as surrogate measures of accident
experience and measures of effectiveness of delineation treatments.(23-26) In roadway delineation
research, speed variance and lateral placement variance have been considered as indicators of the
effectiveness of alternative treatments at reducing errors in the guidance level of the driving task.
Design inconsistencies also increase guidance-level errors, and it is reasonable to hypothesize
that these measures would be correlated with and could complement speed reduction in evaluating
design consistency.