You have to pay attention to the file name of the .ar files of the patches that you make, otherwise they can't work, since it's necessary that they're ahead the city .ar file in file name sorting.
Add some exclamation marks symbols ahead the file name, with also a space between them. Name the patches .ar files like this: ! ! !Chicago_Bridges_Open_Patch.ar and ! ! !Chicago_Bridges_Closed_Patch.ar.
To make the .ar file, use WinRar or 7-Zip program making a ZIP compressed archive with .ar as file extension.
Edit: alright, now you've done a great work with it.
Soon I'll publish it here on MM2X.