Motorways heading south will probably be the heaviest hit, as the last of the season's skiers flock to hit the slopes for the long weekend.
Those planning a few days at the coast could also find themselves stationary on the autobahn, as both the Baltic and North Sea coasts are popular holiday destinations.
Click for a map showing roads likely to see congestion
The ADAC said on Wednesday routes to avoid included the A1 motorway between Cologne and Hamburg, the A3 between Frankfurt and Nuremberg, the A8 between Karlsruhe and Salzburg and the A95 between Münich and Garmisch-Partenkirchen.
Even savvy travellers trying to avoid the traffic by heading off on Saturday could hit trouble, the ADAC warned. Only on Easter Sunday are the country's roads expected to be calmer.
Drivers should try to avoid peak travel times, Rainer Hillgärtner of the ACE drivers' club told Der Spiegel online news site. This meant not heading off mid-morning or early in the afternoon, he added.
Skipping to the end of the break and Easter Monday will see more jams as people return home. Much would depend on the weather, ADAC said - but national weather service the DWD said there could be more ice and snow.
The winter weather still dominating most of Germany may make for dangerous driving conditions. Meteorologist Sabine Krüger said that the north and north east would be the worst affected.