Police closed the A5 in north Wales after scores of drivers parked illegally on the road.
Highway teams were seen taking away cars on the road on Friday near the boundary between Gwynedd and Conwy.
Traffic Wales said North Wales Police shut the road near Ogwen Cottage outdoor pursuits centre in Eryri, also known as Snowdonia, because of "inconsiderate parking".
At least five tow trucks were seen despite calls for sensible parking.
There were fears emergency vehicles would be blocked and, at one point, an ambulance had to be allowed through the congested scene.
One motorist said she "was surprised to see cars actually being towed".
"We were going to park in a proper place... but if we needed any more encouragement to find a proper car park, that was a good incentive," she added.
"And there's a sign saying 'you will be towed' so they can't say 'we didn't realise'.
"I doubt anyone thought that would actually happen."
It followed a similar appeal the previous day from the police force, Gwynedd council, Snowdonia National Park and the National Trust.
Illegally parked vehicles were also towed away from near Pen y Pass car park at the foot of Yr Wyddfa, also known as Snowdon, earlier on Friday.
Traffic Wales said the Highway Code "states that double yellow lines apply to the road, pavement and verge".
Elizabeth Roberts, a local councillor whose ward covers the Ogwen area, said: "It was almost becoming a one-way road with cars parking the way that they were, and it made it difficult for emergency workers to get though.
"Drivers also park in front of driveways so local people cannot get out of their properties, and it has a big impact on families who want to walk around the area when cars park on the pavements."
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