Good question Pesta, most runners are probably training to run marathons, half marathons or 10K’s which will be run mainly on the roads so road work is preferable. However, there are many things you can do to lessen the toxic effects that running on traffic filled roads will produce. Running early morning is the best time to run before traffic has built up in the rush hour, it’s also cooler and more refreshing. Best not to run on a full stomach so before breakfast means you don’t have to be careful about what you eat throughout the day.
Most cities and towns have secret ginnels and cycle and walking tracks and paths away from the roads, or perhaps a river or canal through the town usually have good towpaths along the side. Purchase of an Ordnance Survey Map will have all of these marked. It will also provide a knowledge of the area that you thought you knew.
I think it is quite irresponsible for runners to run alongside traffic on busy main roads, not only are they risking their lives they are making drivers take avoiding action when they encounter a runner on a bend. I occasionally have to run alongside a busy road to make up a circuit, but it will always be on a footpath and be the shortest bit If I can’t find a suitable alternative.
Having said all that Pesta I love road running, you don’t have to worry about where to put your feet, pace can be fast or slow with no uneven surfaces, and you can let your mind wonder where it will without distraction. I am very fortunate though with quiet country roads and long towpaths alongside the canal, most early mornings I can run for hours and never see a vehicle.