Safety concerns close A83 diversion
The diversion road for the closed A83 route in Argyll will also be closed overnight, Bear Scotland has said.
The main A83 was closed at the Rest And Be Thankful after landslip debris broke through defences in the early hours of Thursday.
The alternative route using the Old Military Road is also to close from 19:00 on Thursday until 07:00 on Friday.
Bear Scotland said this was due to safety concerns.
The A83 has now been closed four times in the past six months by landslips.
The latest incident, at about 02:00 on Thursday, saw most of the landslip contained by a new debris fence.
But slurry seeped on to the carriageway, closing the road between the B828 and the A814 Arrochar turn off at the Rest and Be Thankful car park.
The diversion using the Old Military Road was the first time the emergency route had been used.
A convoy system and traffic signals were put in place, meaning it took drivers about 15 minutes to travel along the diversion route in each direction in turn.
The overall delay was between 15 and 45 minutes.
Bear Scotland said further assessment of the geotechnical situation at the Rest and Be Thankful has been undertaken by its engineers during the afternoon.
They advised that, while the clear up operation had been completed, there was still "considerable uncertainty" due to the continued poor weather conditions about the stability of the hillside above the A83.
'Boulders and silt'
A spokesman said: "A large amount of material, both boulders and silt has been disturbed during today's landslide and there is concern that this may be mobilised by the heavy rain which is forecast to continue until early morning.
"On that basis it has been agreed with Transport Scotland that the A83 will remain closed overnight.
"The Old Military Road local diversion route has been a success today keeping traffic flowing under a traffic signal convoy system and keeping Argyll open for business.
"However, given the on-going concern about potential further rock falls and landslides and difficulty in monitoring this, during the hours of darkness, it has been decided to close the local diversion route between 7:30pm tonight and 7:00am tomorrow morning. The standard diversion route will be re-established during this period when less traffic use the road.
"We thank motorists for their continued patience and will issue further updates tomorrow (Friday)."
Motorists will face a diversion of almost 60 miles via the A82, A85 and A819 until the Old Military Road is able to reopen.