Use of Curve Advisory Speed Signs in New Zealand

The use of curve advisory speed signs in New Zealand was investigated. Traffic behaviour at the location of curve advisory speed signs was observed to determine the effectiveness of and compliance with current practice. Alternative methods for determining curve advisory speeds, using road geometry data or accelerometer based systems, were compared with ball-bank surveys. The existing criteria and methods used for setting curve advisory speeds in New Zealand were assessed in light of the above findings and changes suggested. The field surveys found that the current ball-bank criteria underestimated observed mean speeds. A revised ball bank relationship that did not take vehicle speed into account resulted in a much better fit. Allowing the use of alternative advisory speed methods is also recommended.