St. Johnstone Interchange
|St. Johnstone Interchange|
|Location Map ( geo)|
|A9 • A85 • B9993|
|Junctions related to the A85|
St. Johnstone Interchange is the connection between the A85 and A9 Perth Bypass to the west of the city. Both are busy routes, the A9 carrying almost all of the traffic heading north to the North Highlands, Inverness and Moray from the central belt, whilst the A85 connects Perth with the West Highlands, via Strathearn. It is therefore a Grade Separated Junction, with the dual carriageway A9 passing under the A85. The junction was originally built when the Perth Bypass was built. Whilst the A9 is primary and trunk through the junction, the A85 is only primary and trunk to the west.
Works started in late 2016 to significantly change the junction. In order to relieve pressure on the existing road, and also to help open up the land to the north west of the bypass for development, the A85 has been (partly at least) rerouted to the north, to a new diamond interchange junction. This saw three of the four original sliproads closed up. Only the northbound offslip has survived.
Coming out of Perth, the A85 now swings to the north at a new signalised junction near the pre-existing crematorium entrance. This new road curves around between the crematorium and football stadium to a new bridge over the A9. Here there is full access for the southbound carriageway, and a northbound on slip, with signalised junctions either side of the bridge. On the west side, a new road (the B9993) continues north west to the western end of the Inveralmond Industrial Estate, which may also help relieve pressure at the Inveralmond Roundabout to the north. This route is eventually expected to connect up with the new Cross Tay Link Road.
From this new junction, a new piece of road heads south, parallel to the A9, in place of the expected offslip, to the existing west roundabout on the A85. This roundabout has been converted to a signalised crossroads, with the existing onslip removed, leaving just the offslip to complete the junction. The southbound offslip was the first part of the new road to open, on 29th June 2018. At the time, the bridge was incomplete, so traffic follows the new road towards the city centre to reach the existing A85. The Northbound onslip, and the new road parallel to the A9 opened on 12th September 2018, and the final new sliproad, the southbound onslip on 19th October. The new bridge was still not open at this time.
The junction was a modified Dumbbell type junction, with sliproads from the A9 leading to two roundabouts on the A85. That to the west of the junction was a more traditional design, with the sliproads heading away from each other, whilst the southbound carriageway was served by folded sliproads, which both approached the roundabout from the north, the A9 onslip curving round to pass under the A85 bridge. This eastern roundabout is also known as the Newhouse Roundabout. In between the two roundabouts is a traffic light controlled crossroads, primarily providing access to the Tesco store, which sits in the loop of the former sliproads, and the B&Q and garages opposite. These signals actually caused more congestion than the roundabouts.
|Stirling, Glasgow, Forth Bridge, Edinburgh, Dundee (M90)|
|Inveralmond Ind Est|