a Green Line cake? I've been asked to do one for next week and said I'd have to sleep on it.. I've never carved a cake, although a trolley seems pretty basic.. I only found 1 picture in the galleries.. Any thoughts or advice? Especially for the windows? Thanks so much!!

You could premake the windows out of gumpaste and attach to the finished cake, that way you could make sure, that they are straight

Yeah, the shape is pretty simple -- just a tall rectangle, with some rounded corners. Fairly good choice for a first carved cake actually. Bus and train cakes would use similar techniques, if you want to look for other example photos. Like these:
http://www.cakecentral.com/cake-photo_1686487.html
http://www.cakecentral.com/cake-photo_1381917.html
http://www.cakecentral.com/cake-photo_1500025.html

Windows are often just black, white or grey -- either fondant cutouts, candy/cookies, or just smooth BC -- but you can make them look more translucent by painting "streaks" or using piping gel.
http://www.cakecentral.com/cake-photo_1691300.html
http://www.cakecentral.com/cake-photo_1292789.html

Oh my gosh! I didn't realize anyone had responded - I didn't get any notifications! Thanks so much for your help!!!