The road has been monitored for the past couple of years by independent specialist firm Geckoella, which has been advising Somerset Council.
Geckoella co-director Andy King said: "The amount of erosion that's occurring there, and continues to occur, is certainly dangerous for any vehicular traffic.
"We're expecting there to be continuing landslides and coastal erosion at increasing rates.
"It would be very difficult to think of an engineering solution in that particular location because of the height of the cliff and the scale of the landslip going on."
The road is still open for pedestrians usingf the coastal footpath and for non-motorised bikes.
Dr King continued: "Watchet is not alone as a coastal town which is suffering from the impact of coastal erosion.
"A lot of this is about how costal towns adapt and mitigate."
Somerset Council's lead member for transport and waste, councillor Richard Wilkins said: "The situation is unchanged – the B3191 remains unsafe for motor vehicles, but we need to move to a proper legal position with respect to these roads.
"However, we are continuing to lobby for transport investment in our county. When funding streams become available we will lobby strongly on behalf of local communities."
