Does a caravan or trailer need a second vignette?
Yes. A trailer is charged in its own right, so a car towing a caravan needs two vignettes at CHF 40 each. The exceptions are a trailer behind a motorbike, and anything heavy enough to fall under the lorry charge instead (Federal Office for Customs and Border Security, checked 29 August 2026). Buy the second one before you reach the border, not at it.