Well that is exactly my point. I commute in what I call "casper mode." I assume I am invisible and any crossing motorist just doesn't see me, (and I have seen motorists "suddenly" see me) and I keep an eye on a mirror to check that those behind me have seen me. But between the stoplights and slowing at intersections and where motorists may pull out from the curb, I find I ride much slower than I can on an uninterrupted path. My commute is 11 miles and takes me 50 minutes. I can ride a local path (not on my commute... off in a different direction) for 20 miles in just over an hour. Now which is better exercise? Which do you think I enjoy more? And which do you think I go much faster upon? Of course, this is not your typical park type MUP, it is quite wide.

But my point is that we do spend a bit of time on the streets expending energy "dodging" cars. Oh and even if I get all green lights... I still don't blast through intersections... I have had too many close calls with red light runners and those that don't look before turning right on red. I used to do that... If I saw a good green, it was a reason to sprint right on through... but red light runners took that pleasure away.

This is one reason probably why those guys were training in a group... expecting that the size of the group would give them more visibility... and allow them to go flat out. Of course they also had group dynamics... pacing, going on.