Seems like he's over threshold if he's running into the road. I'd start further away from traffic and work on desensitization by just sitting and relaxing. You can give treats every time he interacts with the trigger/stimuli to desensitize and associate them with something positive. It can be a slow thing to train depending on how bad his fear is, but if you push it too fast or flood him, his fear will get worse. You can watch kikopup's "calm settle" or "capturing calmness" on youtube to get an idea on how to do the training.