My Alfie was also very nervous so I used to take him out along a quite busy road and just not say anything to him in the hope that if I was relaxed and unfazed he too would learn to be. We eventually had an unfortunate incident when a bus, large truck, and dust cart passed by us at speed which scared the life out of me as I wasn't aware there were 2 large vehicles approaching behind me. Very fortunately, Alfie just stopped and looked a little startled and then carried on walking so I considered him cured. I then moved on to sitting near my local bus hub where he could experience vehicles stopping and starting with lots of people standing and moving around. We now don't see much traffic on a day to day basis but whenever I take him somewhere built up and busy, he is still very relaxed.