The A83 Tarbet to Campbeltown road will be closed at the Rest and Be Thankful due to heavy rain forecast overnight on Tuesday.
Motorists will be directed onto the Old Military Road (OMR) diversion route from 7pm onwards through Wednesday morning.
This is due to heavy rainfall expected in the Glen Croe area during the evening.
The Rest and Be Thankful is often closed down because of its high elevation and the potential for landslides to occur – making driving on the road hazardous in heavy rain.
The OMR route stays close to the valley floor and operates via a single track
A vehicle convoy will be used to escort traffic through the valley to make it safer for road users.
An assessment on whether to reopen the A83 will be carried out on Wednesday morning however, more heavy rain is expected during the week.
Eddie Ross, Bear Scotland’s north-west representative said: “We’ve taken the decision along with Transport Scotland to direct all traffic to use the Old Military Road from Tuesday evening as a safety precaution given the persistent rainfall being experienced, and a safety inspection on Wednesday morning will determine if safe for us to reopen the A83 for road users.
“Looking ahead, we’re expecting further heavy rain to move through the area over the remainder of the week, and our teams will remain on high alert.