Hi I am travelling across Germany, Italy, Austria and Czech Republic by car in September. I have looked on the web and there are mentions of Nuremberg being a significant freight hub to see freight trains. Can anyone confirm this and also recommend any other potential places in Italy (Trento and surrounding area); Salzburg (Austria) and Prague?
Whoa, there's a big open question!
The best thing is to research in detail information about the relevant railways using books, regional internet forums, magazines, web sites etc.
Nürnberg has a big marshalling yard, but there are lots of other big freight hubs - and busy freight lines - around Germany.
I recommend you research noted well known freight watching locations. The best places are often but not by any means always, close to a marshalling yard hub.
Bahnbilder.de is a good place to look for photos of particular locations and / or loco classes
http://www.bahnbilder.de/name/bilder/hierarchie1/Deutschland.html
Well known busy spots in Germany include:
Hamburg Harburg
Köln West
Berlin Outer Ring line:
http://gwizz.piwigo.com/index?/category/70-april_2013_saarmund_berlin_aussenring
The river Rhine right bank route (anywhere along the route):
http://gwizz.zenfolio.com/germany_oct_2011
Hannover
Lehrte
anywhere on the Hannover - Bebra - Wurzburg - München route
Dresden - Decin - Praha (Prague):
http://gwizz.piwigo.com/index?/category/191-elbe_gorge_koenigstein_and_bad_schandau
http://gwizz.piwigo.com/index?/category/190-dresden_stetzsch
In April, I saw nearly 40 freights in 4 hours just east of Munchen:
http://gwizz.piwigo.com/index?/category/185-hattenhofen_near_munchen/start-40
If you are travelling by car, you have the advantage of being able to lineside on these routes
In Austria/Italy, one of the main trunk freight routes is the Brenner route Munchen - Innsbruck - Brennero - Bolzano - Trento. Another Austrian trunk route is Salzburg - Tauern tunnel - Villach
Finally, on my April trip to Dresden shown in the picture links above, we cut through the Czech Republic by car. The area along the northern border is an amazing mining/industrial area, like the UK industrial heartlands of 40 years ago. We saw heavy coal trains hauled by clapped out electrics running on a Sunday evening.
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