[welterde]

That has very little to do with the ICE train itself though, which can do above 320 km/h just fine in regular service (on international connections though, since in Germany the global train speed limit is 300 km/h I believe).

While the high-speed tracks in Germany are indeed quite a bit of a patch-work, there are over 1000 km of track certified for >= 250 km/h (as of 2015; quite a number of more lines got finished since then, but I could not find the updated number that included them) and by now really rather long corridors are very high-speed. The route from Munich (south of Germany) to Berlin is now mostly covered with upgraded routes for example. I think the 4 hours for that route are quite competitive to Shinkansen times. The fastest Shinkansen route (from the listed operating speed the only one that actually operates at 320 km/h; all others only operate at 260-300 km/h) is the Tōhoku Shinkansen line, which takes 3 hours and 20 minutes for the same distance traveled.

[jhugo]

The lack of dedicated tracks for high-speed passenger service matters a lot though. It’s part of the reason why those (very impressive) scheduled Munich-Berlin times are so often not achieved. The “slot” for the service is relatively small because slower trains (in particular freight) must be scheduled as well, so if the slot is missed for any reason, delays can compound very badly. I take the train between Munich and Berlin reasonably often and it’s usually running late, and sometimes by an hour or more.

[welterde]

Reliability is certainly one aspect where dedicated tracks helps a lot, but is not the only solution (see for example Switzerland). For Germany the issue is the overall too large utilization of the network and the large backlog of required maintenance of the rail infrastructure (in my opinion).