Warning signs move as landslides intensify

08 October 2008

Transport Scotland is to erect new warning signs and consider expanding drainage capacity across the 10% of Scotland’s trunk road network at significant and growing risk of landslides.

The Scottish Government’s study to determine the likely locations of landslides, ordered after debris flows in August 2004 forced the closure of a number of trunk roads and trapped 57 people, has concluded that 386km of road are at risk.

This is almost three times the length of the 136km of routes the study initially identified as suffering from the hazard (Surveyor, 23 June 2005). Given the widely-dispersed nature of the hazard, the study concludes that ‘few’ engineering measures, such as creating channels allowing debris to move safely or installing barriers to prevent material from reaching roads, will be appropriate. Instead, the study – noting the growing risk of landslides due to predicted increases in intense rainfall attributed to climate change – recommends that landslides are detected and motorists warned.

Transport Scotland is testing a system for triggering warnings, and has reported that last October, a threshold of rainfall levels expected to lead to a landslide was successfully tested on the A83 Rest and Be Thankful road. This highlighted two hours before a landslide that rainfall had been sufficient ‘to cause the debris flow to be inevitable’.

However, further data is needed to validate this finding. Landslide patrols are also recommended during periods of intense rainfall to raise the alarm that debris flows are occurring. Variable-message signs and, potentially, flashing lights attached to new landslides static road signs – adapted from the current rock fall sign – would alert motorists.

But Andrew Fraser, accident unit manager for central Scotland, questioned the findings.

‘Do we know how motorists will respond to these signs? And will there be agreed diversions with local road authorities?’

Scottish road network landslides study

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