http://Zierke.com/project/ baltic_seatrain/scandlines-dk/fahrzeit
Travel time table

København–Berlin in 4 hours?

Running time result of existing Scandlines suggestion, and possible improvements

Assumptions: Fast car/railferry with 45 knot top speed (loaded), standard mooring process.
Distance (km) Track Speed (km/h) Average speed (km/h) Time interval (min) Time
København H 0 0:00
Høje Tåstrup 19.6 140/180 90 13 0:13
Høje Tåstrup 1 0:14
Ringsted 44.304 180 127 21 0:35
Ringsted 1 0:36
Nykøbing F 82.946 140/120 106 47 1:23
Nykøbing F 2 1:25
Gedser (after track repair) 22.952 100 66 17 1:42
Carferry timetable buffer, similar to Puttgarden-Rødby 5 1:47
Gedser boat 5 1:52
Rødsand Edge 8 knots 12 2:04
Rostock Approach Ton 12 25 2.29
Rostock Approach Ton 14 13 knots 3 2:32
Rostock Approach Ton 16 10 knots 4 2:36
ready for mooring 10 2:46
Warnemünde boat 4 2:50
Warnemünde 5 2:55
Rostock Hbf 13.1 120 37 21 3:16
Rostock Hbf 3 3:19
Berlin Lehrter Bf after improvement "up to 160 km/h" 216 113 115 5:14
Extra time to run via Spandau or Biesdorf with a DMU 20 5.34
Possible improvements by Scandlines
Special ferry shunting system, allowing non-DMU operation -15 5:19
Automated mooring system, with similarities to the system used by Tranz Rail -4 5:15
Optimizing train and ship's daytime payload for low-wash operation, avoiding speed restrictions -4 5:11
Precaution for fast turning of the ferry -1 5:10
Sum: -24
Possible improvements in Germany, with good chances for implementation for enough trains
Restoration of pre-WWII running time on Warnemünde-Gedser. Coexistence with dense S-Bahn traffic by help of shorter block and bidirectional running, or by gaps in S-Bahn traffic. -10 5:00
Berlin - Rostock: 160 km/h upgrade instead of "up to 160 km/h" (needs pressure by Mecklenburg-Vorp.) -15 4:45
Sum: -25
Possible improvements in Denmark, with good chances for implementation for enough trains
Nykøbing F- Gedser upgraded to 140 km/h -4 4:41
More flyovers for København H station throat + København-Ringsted signaled for higher capacity -4 4:37
Ringsted - Nykøbing F upgraded to 180 km/h, with the exception of Masnedø-Orehoved -9 4:28
Sum: -17

I do not see chances for 3-digit-million € track improvements, in order to reach "4 hours", without running 2-hourly traffic first, at 4:30.

To the letter text.