The Scottish Road Network Landslides Study made a number of recommendations for landslide management and mitigation. Amongst these was that ‘wig-wag’ signs could be suitable at sites with specific conditions, particularly those sites at which debris flow events occur on a regular basis. Such signs incorporate a standard rockfall/landslide red warning triangle, flashing lights, and a sub-plate that that warns of ‘Higher risk when lights flash’.
A trial of such signs commenced on the A83 in 2011 and was centred on the section of the route that includes the Rest and be Thankful. As part of this trial it was intended that a detailed technical and perceptual evaluation of the signing arrangements be undertaken. Accordingly, the aims of the work presented in this report were to examine the efficacy of the operation of the wig-wag signing arrangements at this location, and to explore the perceptions and attitudes of road users to these specific signs.
It is broadly concluded that the trial has had a satisfactory outcome. With one exception, the debris flow events that occurred during the period of the trial were within a period when the lights were activated. The one event that did not occur during such a period was of a somewhat different character and further investigation is recommended.
The period during which the lights were activated and were not associated with a debris flow event corresponds to between 11% (2011) and 15% (2012) of the days of the year; this is considered to be broadly acceptable in the light of the rainfall triggers that are currently available 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. It is, however, suggested that widespread media promulgation that the signs are switched on, and an associated misinterpretation of that fact, may be the source of the erroneous suggestion that ‘mid-Argyll is closed for business’ at such times. As a result, one of the key recommendations is that the practice of placing notifications that the signs are activated on the Traffic Scotland website be discontinued.
The A83 Rest and be Thankful locality is known for the frequency with which debris flow events occur, much more than any other part of the trunk road network in Scotland. It is thus well-suited to the use of this type of temporal warnings. The potential application of wig-wag signs to other parts of the network is limited and any proposals should be the subject of detailed location-specific assessment.

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