Here is how i did it:
It isn't hard. When crossing the street with your dogs, you should ALWAYS stop (with or without cars passing) if he fails, you stay on the sidewalk and call him back.
When crossing, always let the cars pass first (the dog doesn't understand if someone let you pass, they need to wait for the cars to pass first)
Try first at night with less cars or calm streets.
And most important: be consistent!! If you are in a rush and forget it, the dog won't understand why he shouldn't do it...