I do quite a bit of training on the track bike on the road. But I am generally very intentional about where and when I do that riding. For example, I will ride on the street in front of my house early in the morning or in the middle of a week day. Or on weekends I will drive over to the local business park that has wide roads and little weekend traffic. I generally cannot fathom riding fixed gear without brakes in normal traffic or on a crit course.