fix #1504

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@17356 29f149b2-0c63-11e1-8f5c-a347f6a9acd0
refactoring refs #12

git-svn-id: http://svn.code.sf.net/p/sumo/code/trunk/sumo@17357 29f149b2-0c63-11e1-8f5c-a347f6a9acd0