Maybe I should say it is not very safe for me to do intervals on the road. I tend to push myself to the max when doing intervals, then recover, then push hard again, etc. When I'm pushing hard, I'm in a big gear and going for the max rpm possible. My sensory awareness of stuff around me is decreased quite a bit. I think pushing yourself that hard is better for stationary bike or a race - where there are protections from regular traffic.