that, indeed, is a problem. since I just read quite some requests on this forum, lets make one for myself then:
can you replace the double decker metro train with a dutch NS train? I've added a description to every one, so if you'd like more photo's, just copy the dutch words in google pictures. Just pick the one you like the most to mod:
the so called 'hondekop', translated as doghead, is the most common intercity short distances train (stops at every station, no idea how you guys call that)
http://upload.wikimedia.org/wikipedia/commons/e/ed/NS_894_als_stoptrein_van_Tilburg_naar_Deurne%3B_19_april_2008.jpg
this is the replacement for the hondekop, quite a few are driving around now, now idea what it's called.
http://www.nicospilt.com/anderen/NL20080124_2402.JPG
and here we have two versions of the mass transport intercity trains double-deckers, the first one is an old model, the second quite new. The first one's probably the most easy to create. (these trains are fast trains, translated, they just stop at big stations, dutch name: dubbeldekker trein, or double-decked train)
http://members.multimania.nl/timgoorman/3907707rtd1.jpg
and finally the so called ,,koploper", or headrunner. Koploper also means in Dutch the leading party, so they mention the koploper is the best train available. Just stops at big stations.
http://www.marklin.nl/nieuws/afbeeldingen/Schiphol%20Koploper%20800.jpg/image_preview
Most of the times, NS combines two trains, so the metro doubledecker would be quite nice.
If this is too much work for you, isn't it just possible to change the doubledecker train with a train from the CXL09 ploppable trains mod? Think it will be the easyest way to make intercity passenger trains drive through our cities.
The NS trains would look great with the Rotterdam metro, by the way.