A literature review undertaken for Transit NZ has found that delineation has a significant effect on driver behaviour with, for example, shoulder rumble strips reducing run-off-theroad crashes by between 22% and 80% (average of 32% for all crashes and 44% for fatal run-of-the-road crashes). The concern that enhancing roadway delineation may sometimes be accompanied by an unwanted increase in drivers’ speeds (known as behavioural adaptation) is not borne out by the research and appears to be a phenomenon associated with a few restricted situations (e.g. where a centre line is added to an otherwise unmarked road). The preponderance of the evidence supports the conclusion that profiled edge lines and centre lines provide drivers with positive guidance and produce significant reductions in crashes as a result of improving drivers’ lateral position. Further, unlike other safety measures that show decreased effectiveness over time due to a novelty effect, profiled lane delineation continues to work regardless of driver familiarity. There is no published research to suggest that profiled edge lines will decrease the effectiveness of a profiled centre line or will result in an increase in crash rates or an increase in the severity of crashes. However it has also been noted that local conditions have a major influence on the level of benefits that can be achieved through improved delineation.