The A9 trunk road between Perth and Inverness is a unique route connecting two cities while serving several smaller local communities, numerous tourism and recreation sites and long-distance freight. This >170km section is predominantly single carriageway with sporadic dual and WS2+1 sections, which combined with the varied topography and unique journey purpose profile of road user results in limited overtaking opportunities with increased journey times and driver frustration. While the accident rate on the route is low the severity of accidents is higher than national trends.
In 2013 work began on the DMRB Stage 1, 2 & 3 assessments to deliver the various individual projects that will complete the A9 Dualling Programme by 2026. The route is particularly environmentally constrained along its length while >100km lies within the Cairngorms National Park.
We developed the 2012 Base A9 Dualling Traffic Model (A9DTM12), a >170km microsimulation model reflecting the unique operational characteristics of the route. This was interfaced with the national Transport Model for Scotland for strategic forecasting, environmental assessment and scheme design. Our role involved the DMRB Stage 2 and Stage 3 Traffic and Economic Assessment for the three dualling projects between Glen Garry and Dalraddy, which lie entirely within the Cairngorms National Park.