Which form of exercise has less impact on your joints running on the street or running on a treadmill?

From the opinion of one who has run on everything from dirt trails, to gravel paths, to treadmills, roads, grass and sidewalks, these are my discoveries: Treadmill running should be done as rarely as possible. Some treadmills are lighter on your joints than others, but my legs hurt far more often in the winter due to treadmill running than during any other seasons. Street running is relatively easy on your joints, which was much to my surprise initially, but it is obvious that it does less to deteriorate your legs. My preferred surface on which to run is a trail, so if you have trails near you choose that first. The exception is, on relatively long runs, trails can get repetitive. I do my long runs on roads. But back to the initial question, running on the street has much less impact on one's joints than running on a treadmill.