How can I help my horse's spooky nature?

you need to desensitize him - he spooks because he does not know what it is. Try sacking him out - as far as the traffic try walking beside to road and around the things that scary him. remain clam at all times when doing this. he will get better once he understand what it is and will not hurt him. What he is doing is natural for a horse - a horse is a prey animal - when faced with something he does not understand his Instinct is to flee. let me know if this helps