Pre trained vehicle detection network I'm looking for a pre-trained net recognizing vehicles, something like the Inception network for images. 

If that is impossible to find which vehicle detection algorithm would you suggest, possibly implemented in tensorflow?
You can take a look at the YoloNet which detects Objects based on Pascal VOC 2012 dataset. 
Here is the link to it : https://github.com/pjreddie/darknet/wiki/YOLO:-Real-Time-Object-Detection

You should be able to detect vehicles with this pre-trained model.