Until recently all vehicles attempting to cross a border were required to bear near the rear number plate a regulation nationality sticker designating the country in which the vehicle is registered. This is still technically true for all vehicles registered outside the European Union and for all vehicles whose numberplates do not have the nationality built in (as all newly registered vehicles do). The European Union (EU) consists of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, Netherlands, Northern Ireland, Portugal, Spain, Sweden, and the United Kingdom.
As I described in the Why Drive? chapter, in most cases border-crossing is a quick and hassle-free process. The 1995 Schengen Agreement abolished standard border controls between EU countries, plus Iceland and Norway. Typically, upon entering an EU country from without the EU, tourists receive a passport stamp; however, tourists do not receive stamps when crossing from one to another EU country. In fact, customs booths between EU countries have been dismantled, and a mere EU sign (blue sign marked by a ring of gold stars) coupled with the name of the country being entered marks such frontiers.
Potentially you are subject to passport checks and searches of your person and vehicle upon crossing a border involving a non-EU country. Sometimes you'll be required to slow down and stop before the guards simply wave you through. A circular sign reading "Douane Zoll" is a signal that you must stop. Most likely you'll just queue-up in your vehicle, wait a minute or two, hand each passenger's passport to the guard when you reach the station, flash a smile, wait a moment until the guard returns the passports, and proceed forward a couple hundred meters to the border station of the next country (where you'll repeat the process). Sometimes the guards will want to see your vehicle's registration and proof of insurance. Sometimes, even, your vehicle will be searched. If you're chosen for a search, follow the Customs officers' directions and chalk it all up to experience; it's not too time consuming or nerve-wracking—unless, of course, you've got illegal substances or items with you. It goes without saying that you should never bring illicit drugs or weapons across borders. If you're transporting hitchhikers or others who haven't had the opportunity to gain your trust, politely and up front make it known to them that they must get out at the border and lug their things across on foot. If your vehicle has significant cosmetic damage to it, point it out to the Customs officials and have them note it on your passport; otherwise upon exiting the country you might be suspected of having been in an accident in that country and fleeing your associated responsibilities. If a country requires you to declare your vehicle with Customs, you'll probably be obliged to pay customs duty and tax if you leave the country without the vehicle.
Here's a trick to be aware of. If several fuel stations are clustered on your side of a border, fuel is probably more expensive in the next country; fill up before crossing.
The auto clubs of many countries maintain offices at the borders. These offices may sell everything from auto insurance to maps to guidebooks.
In the country-by-country descriptions, I delineate the duty-free customs allowances of each country. In relation to those allowances, you should know that the following countries comprise the European Community (EC): Belgium, Denmark, France, Germany, Great Britain, Ireland, Italy, Luxembourg, the Netherlands, Portugal, and Spain.
Finally, note that many border crossings close overnight, from, say, 8:00 or 9:00 p.m. to 7:00 or 8:00 a.m.; but most stay open until 10:00, 11:00, or 12:00 p.m. in the summer.