Each country has issued a law to require police, sanitation workers, High-speed highway law enforcement personnel etc to wear high visibility clothing such as a safety vest, safety raincoat etc. But recently a group of people have started to appeal to wear this professional clothing for civilian using.
Civilian using is a very broad. People who need to be constantly exposure in the road should wear a high visibility vest too, such as the cyclist, motorcyclist, night runners, night walkers, hikers etc. Then some people doubt that is it really necessary? As far as I'm concerned, it is necessary! As you know, nowadays, traffic accidents happen more and more frequently. According to the data statistics, one of the important reasons is that drivers usually cannot see the pedestrians clearly especially at night! But by wearing a hi vis vest, it will increase the high visibility. Therefore it can give a warning single to the passing by traffics. In this way, most of this kind tragedy will not happen.
So for our own safety, we should wear a hi vis clothing when we are plan to do exercise at night or need to expose on the road for much time.