It looks like you're booked to travel via the new line!
According to this link:
https://www.railtech.com/infrastruc...h-speed-rail-launched-in-denmark/?gdpr=accept
Koge Nord is a new station on the high speed line, while Koge is the classic track station; they are separated by a motorway, but joined by a pedestrian footbridge (a photo of these two stations appear in the link above).
The attached report has a map showing the new line. It would make sense for the EC trains to run via the new tracks to help reduce congestion on the classic main line.
Great - thanks - that's helpful.
Though in fact, checking various maps, it seems that the other station by the new line's Koge Nord station is not Koge station on the classic tracks, as you say, but Koge Nord on the route of the (metro-style?) S-trains from Copenhagen to Koge. The classic line joins the S-train route a bit later, and both then go to the actual Koge station some distance further on. There is no common station between the new line and the classic line there; the former diverges before the latter meets the S-train line.
I see that the speed planned for the new route is not exceptionally high by European high-speed standards, though it's a bit faster than existing Danish lines. - but the new line means that the higher speed can be maintained for some distance, which of course is what makes the difference, rather than worrying about pushing the top speed up a bit more. [Interestingly, in this context, many people in the UK fret about the lack of high-speed trains here, when it's not the actual top speed that's the problem, but having a route where you can maintain it. The improved Danish lines are planned to have 200kph and 250 kph running. But the UK has had trains traveling at the former speed for literally decades, and in recent years some UK trains are not much below the latter. The problem is much less the top speed, than being able to run at it more consistently.]
Getting back to the Copenhagen-Hamburg service, what's notable is that the journey time using the new line is hardly different. Perhaps because the new line is a relatively small proportion of the overall route; possibly because the rolling stock on that service can't make full use of the possible line speed anyway. But as you say, it could be routed that way primarily to improve capacity on the old line. Although there are only 3tph on the major route to Odense, which forks from the line in the Hamburg direction at Ringsted, there are quite a lot of local trains at least as far as Ringsted, which stop at various places and so get in the way of longer-distance services even if the latter aren't particularly high speed. Although the new line joins the original route before Ringsted, it seems to be 4-track for that section - presumably that's part of the new line scheme since it seems unlikely it suddenly switched to 4-track there previously.
Thanks again for clearing this up for me. And it looks like the faster of the Odense-Copenhagen services (including the Fredericia-Odense-Copenhagen services which connect from the Hamburg trains) also go via the new line after Ringsted, so I'll get to try it in both directions!
