Evaluation of a novel road-based landslide early warning system

Novel early warning signs for landslides were introduced on the A83 strategic road in Scotland, incorporating a standard rockfall/landslide red warning triangle, switchable flashing lights ('wig-wags') and a sub-plate stating 'Higher risk when lights flash'. A trial on these signs focused on the Rest and be Thankful area of the A38, where landslides are a common occurrence. The efficacy of the operation of the wig-wag signs and the perceptions and attitudes of road users to the signs were assessed. It was concluded that the trial had a satisfactory outcome. During the trial period, 15 of the 17 debris flow events (almost 90%) occurred when the lights were activated; the two events that occurred when the lights were not activated were of a somewhat different character, but were nonetheless classed as 'false negatives'. The periods during which the lights were activated and were not associated with a debris flow event corresponded to 12-19% of the days of the year; this is noteworthy, but considered to be broadly acceptable in the light of the currently available rainfall triggers to determine the timings of switch-on and switch-off. The results of the driver survey element of the work indicate that, in general, desired behaviours are promoted by the use of the signs.