Driving and renting a car
Slovenia uses a vignette system on its motorways, and rental cars typically come with this pre-arranged, though it's worth confirming coverage for the specific route. Driving is on the right. The Vršič Pass is Slovenia's highest mountain road, with dozens of hairpin turns, and while paved and well maintained, it's slow going and can close in winter, so check seasonal status before planning around it.
Why compare local rental companies
Slovenian rental agencies are generally standardized given the country's EU membership, but confirm whether a quote includes the motorway vignette by default, since this is occasionally itemized separately. Cross-border trips into Italy, Austria, Croatia, or Hungary are usually straightforward given Slovenia's central position, but confirm any documentation needs for non-EU destinations on your route.