Excursion from Warnemunde to Berlin on a Friday. Ship leaves at 11:59 pm. By what time do we need to leave Berlin to ensure that we safely catch our ship? And what are the worst hours for traffic leaving Berlin? I have to believe that we could leave Berlin at 6:30-7 pm and safely catch our ship.
I'm assuming you are going by public tramsportation from Berlin to Warnemünde. If so, then I myself would take a direct RE train to Rostock Hbf from Berlin Hbf. That takes over 2.5 hrs. If you don't take a direct train, you'll have to transfer in Schwerin (formerly of Mecklenburg-Schwerin), which rven takes longer getting to Rostock. I would say arrive at Rostock by 22:00, early but I like the time cushion. Since there is no direct connection from Berlin to Warnemünde, the S-Bahn at Rostock Hbf takes you to Warnemünde in less than 1/2 hr.
I don't like cutting it close, rather have the time to linger at Rostock Hbf. What I noticed in particular at Rostock Hbf is that it had more stairs than usual, which isn't really great with a lot of luggage, don't know about an elevator.
I would have dinner at Berlin Hbf, better than at Rostock Hbf, way more choice at Berlin Hbf., then catch a direct RE arriving no later than 22:00.
Fred, sorry I was not clear. We are going by van with a private driver who will drive us to Berlin in the morning and then back to Warnemunde in the evening.
It's impossible to predict traffic. Maybe start checking google driving directions at the corresponding time for that route for a few weeks to get an idea of how often there is serious traffic between those locations. To be on the safe side, however, I'd add 3 hours to the estimated normal driving time. German staus (traffic jams) are legendary.
Try this. Enable the traffic report feature on Google maps and check everyday around the time you want to travel. That should give you an idea of how Stau-prone your route is.
TomTom recently released their yearly traffic index report, which ranks major European cities on traffic congestion. I forget Berlin's exact ranking. It was relatively low for a European capital city, but still the second-most congested city in Germany, behind only that legendary Stau-generator, otherwise known as "Stuttgart".
Since you might very well encounter a Stau, supposedly worse than the traffic jams in Southern Calif., which makes traffic unpredictable, is there the possibility of dropping this van ride and taking the train, which does have a definite time of arrival in Rostock. Your main concern is to get to Rostock Hbf. from which you can take a taxi or the S-Bahn to Warnemünde. It's much less predictable going to Warnemünde by van. If the ship departs at 23:59, it may start boarding at 23:20 or even earlier. I haven't done a cruise of any type, only a ferry from Hamburg.
If you stick with the van, maybe leaving Berlin at 17:00 would be better to be on the safe side. But that cuts into the day seeing the Brandenburg Gate, Unter den Linden, etc.
Does the cruise company offer their own side trip to Berlin? If they do, take it. It might cost more, but if their own tour is late returning, I'm sure they would wait for it, but I doubt if they would wait for your privately arranged driver (particularly if they offer a tour themselves). The chances of getting delayed and arriving back late are pretty small, but the consequences of getting to the dock in time to see the cruise ship sailing out to sea are pretty grim.
If there is no land package from the cruise line, go by regional train. There is an RE leaving Berlin Hbf at 18:44, with a 37 min change in Rostock, arriving Warnemünde at 22:21. You can do this trip with a Quer-durchs-Land-Ticket for 50€. Depending on when you leave in the morning, the QdLT might also cover all or part of your travel to Berlin.