Keep them in a safe run. They'll be vastly safer, from cars and from predators, in a run, and you can keep them happy and enriched by adding lawn clippings, weeds, veggies, scraps, and other things to scratch around and play in. If you can get them on a solid recall, i.e. they'll come to you whenever you call, you can let them out for supervised free-range time. Otherwise, as you live near a road, you should keep them penned up. Not only is the road a danger to them, they're a danger to drivers- if one jumps up when a car approaches and ends up splayed across the windshield, it could block someone's view and they could crash, or they could swerve to miss the chickens and crash.