Railway line right next to the road on the way out the Greymouth. I suspect that is a train just coming round the corner - lots of coal trains up and down, coal is mined all over the coast and trucked (or rarely railed) to a depot, then on the train through Arthur's Pass to Christchurch. So the roads can be a bit busy, although I didn't have any problems. In my experience it's not the truckies that I have to worry about, it's the morons who forget that they're driving a campervan or towing a caravan... so their vehicle is 30cm wider each side than usual.