European driving rules that often catch foreign drivers off guard
Most driving rules in Europe are what you'd expect: drive on the right, follow the speed limits, wear a seatbelt. The ones that cause problems are the smaller, country-specific rules that don't come up unless you already know to look for them.
Winter tires aren't optional in some countries
Austria, Germany, Switzerland, and several other countries require winter tires by law during specific months, usually from roughly November through April, regardless of the actual weather on the day you're driving. Renting a car with summer tires and driving into one of these countries during the required window can result in a fine even if the roads are dry.
If you're renting rather than driving your own car, ask specifically whether the tires fitted meet the destination country's winter requirement, not just the rental country's.
Headlights on, even during the day
Several countries, including the Czech Republic, Slovakia, Poland, and Slovenia, require headlights on at all times while driving, day or night, all year or during specific months depending on the country. It's an easy rule to forget if you're used to daytime running lights being optional.
Reflective vests and warning triangles are mandatory equipment
Many countries, including Austria, France, Italy, and Spain, legally require you to carry a reflective safety vest and a warning triangle in the car, and in some cases the vest has to be within reach of the driver's seat rather than in the boot. Rental cars sometimes include these, but not always, so it's worth checking before you leave the rental lot rather than after you've broken down.
Speed limits change with weather, not just signage
Some countries lower default speed limits automatically in rain, even without a posted sign saying so. Italy, for instance, reduces default motorway limits in wet weather. This isn't always obvious to a visiting driver used to fixed speed limits regardless of conditions.
Blood alcohol limits are lower than you might assume
Most of continental Europe sets the legal limit lower than the UK or the US, and several countries, including Hungary, the Czech Republic, and Slovakia, have a zero-tolerance policy with effectively no legal limit at all. A single drink that would be fine at home can put you over the limit, or over a zero threshold entirely, somewhere else on the same trip.
Right of way at roundabouts isn't universal
Most of Europe gives priority to traffic already in the roundabout, but a few areas and older road layouts still follow different local conventions, particularly in parts of France with older "priority to the right" rules on certain roundabouts. When in doubt, slow down and watch what other drivers are actually doing rather than assuming the rule you know applies everywhere.
The practical takeaway
None of these rules are unreasonable once you know them. The problem is that they're rarely posted clearly at the border, and a rule that's completely normal in one country can be an expensive surprise fifty kilometers later. A quick check of the specific countries on your route, before you leave, covers most of this in a few minutes.
