I would like to take a picture of a street during the day to depict how much traffic and cars there are on the street. Is there anyway to do this with a long exposure photograph? I have a Nikon D90 and I set the f stop down to 1/16 (the lowest of my lens) and set the time to 2 seconds. Doing this, the exposure is almost saturated when taken around 5pm with the sun setting behind a tree. Doing this, the cars passing by were very hard to make out against the stationary background, being visible as a blur in the color of the car.
Perhaps this is not possible and I should just do this at night where the cars lights are much brighter than the background.
Please suggest how else I might depict the traffic in a photograph? Are daytime long exposure photographs even possible?