I guess I would just ask you "why"? There really is no reason for it and it seems to me that you are needlessly putting your dogs at risk. Bad things can happen in a flash. Despite how much you trust them; they are dogs and have their own thought process. Even the most well trained dogs will have a moment of weakness. Use the leash and save the "off leash" moments for dog parks.
I have to agree with you, completely.
There IS a time and a place for everything. Walking your dog off-leash in open spaces/fields/parks/trails/etc without cars nearby, and where you have a full view of aproaching people/dogs, that's great. But I am actually disturbed when I'm driving and I see people walking with off-leash dogs by the streets. Like, to the point of slowing down to a coast where the speed limit is 50 mph and honking/yelling at the people. I don't want to hit a dog. I don't think I could even drive again if I did so. Walking a dog off-leash near cars and other people/dogs is absolutely endangering their life, and for a few more feet to explore? That's a very silly reason to risk life and limb. If I'm walking in an area with chances of other dogs coming up or traffic in the area and I want to give my dogs more freedom, they go on long leashes. They don't even test the limit of their long lines, they check in on me constantly and Fozzie even heels half the time hoping for treats, and they both have great recalls. But I cannot trust the world or their instincts or myself to respond at the right time 100% of the time and if they were hurt or killed because I didn't choose to leash them I would have no one to blame but myself.
Especially with high drive dogs, like Kelpies, Border Collies, terriers, etc, which have been bred to act on instinct for hundreds of years... a tire rolling by, a wild animal/cat/squirrel dashing across the street, even something blowing in the wind that piques their focus for a second can result in a dead dog.
I have also seen dogs die because of over-confident owners letting them "explore" on the sidewalk alongside cars. A 12 week-old Lab puppy once. I'm sure if those dogs had the consciousness to choose between life and the ability to sniff more bushes, they would have chosen to live. =/