So, I have this idea for a portrait that I want to do. Here in Ottawa there is a great place where the road splits into two and goes separate ways, so with a long exposure the lights of the traffic would look really cool, but at the same time I would like to have my friend in the photo standing still, making it look like all the traffic is wizzing by him. So I thought here is how I might do it, but I'm not sure. Set up camera on tripod, and take a long exposure showing just the traffic without him in the shot, then cover the lens, my friend moves in front of the camera and I hit him with a shot of the flash, and then we would end the exposure. Is this the best way to do this? Will I get the desired effect? please help.