AHC: Bridge to Prussia - Danzig and a demilitarized railroad line

The picture above describes a transportation system in use in Richmond in 1919. It got me thinking...Your challenge, if you choose to accept it, is to somehow enable Gustav Stresemann or equivalent pre-Nazi German leader to secure a demilitarized railroad connection to East Prussia in late 1920s using a system where the German railroad connection doesn't disturb the Polish traffic connections and rail line to Gdynia because it goes over (or under) it by using bridges/tunnels to go above/under the Polish railroads and major roads.

http://upload.wikimedia.org/wikipedia/commons/9/9d/Is_Two_over_one_Railroad_Fare.jpg

If such a connection could be secured before the Great Depression, how would it affect the German-Polish relations and the domestic politics of Germany?
 
Assuming this does not involve any farther changes, I can't see how this influences Polish-German relations, or German politics. Danzig is still a free city, and a railway won't satisfy the 'get your stinking paws off our corridor you damn dirty Poles' crowd. OTOH this will severely damage the reputation of any Polish government unfortunate enough to be in charge at the time, as this represents a concession in a vital region.

By the way, how much would this elaborate construction cost Germany in comparison to extra ferries?
 
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