
Buster was petrified of traffic. When I felt he was confident with going out on walks (about 6 months), i took him for a walk next to a busy road, as soon as he saw the traffic he freaked out

I was too frightened to take him back there and try again because he nearly pulled me over. I was a bit freaked out myself as every walk he's had, whenever a car has passed us, I've given Buster a treat, but that positive association was not enough when he was faced with a very busy road :(
It's only been recently that I have felt confident in my handling of Buster to try to get him over his traffic fears. What I did was to take him for a walk along the busy road but
not right next to it, there is a large grassy area and we stayed as far from the traffic as possible (about 40ft), whenever he felt like it was scarey he would stand still and watch the traffic, I never forced him to walk on or spoke to him atall, just waited untill he felt he could walk (I've got a bit about this in my blog).
The 'no-nonsense' approach will make Buster much worse (he'll freak out if he feels he's being forced into confronting things he's unsure about) also, when he was really nervous of the traffic, any enticing with treats had the same effect it was too much pressure on him, I just stood with him and waited untill he was ready to move on. As he got a bit better, I would then give him treats for walking when cars went past, now occasionally he'll stand still if a bus or really noisy thing is passing us, but on the whole he is really good.
Oh - another thing, I never bothered about getting him to walk 'nicely' at the begining, he could sniff around and pull me towards interesting smells on the grass as much as he liked as I thought this would help build a positive association for him (lovely smells to sniff with traffic noise about).
You need to find your pups comfort level - that is how close he can be around traffic without it worrying him, and get him used to it from that distance, gradually get closer over time, but never force pup to be close to the traffic it will make him much more frightened. Another thing - don't panick, and dont rush him.
Now Buster will walk 'nicely' past the traffic, right on the pavement next to the road, he's even carried on walking with me when a police car zoomed past us with sirens going :)
ETA - Doh!! just noticed MarianneB has allready advised and with much less rambling than me!