That's for racing in a velodrome...those bikes come without brakes, it is not normal to ride them on the street...although with brakes fitted it is ok. Those bikes can go 60-70 under the right conditions...racing I mean.
I hit 78 going downhill at Noosa and I don't recommed it. Craig Walton did 96 downhill and some say he's done 100...he's the husband/coach of Olympic Gold winner Emma Snowshill.
EDIT....78 was not on a fixed wheel.....I said downhill, that's done at 120-140 rpm....
I have to edit again.....for cycle guy, 78 downhill is normal in bike racing, I didn't say on flat, no way....you said you raced bikes, me too....Triathlon and on the road. But you are right what I said is irelevant to this topic.
EDIT AGAIN: Cycle guy, I definitely know my stuff, 60 kph with the wind is entirely possible, I have done 56-58 for short periods, btw, I am an age group triathlon winner....60 in a velodrome is common enough....60 downhill is nothing, 70's are common....on a straight downhill such as Noosa or Coppin's Crossing, Canberra..it's not even straight, I raced there and saw 2 people go over the bridge, 1 guy killed and he may have been foolish, but definitely well in the '70's. Sorry my info doesn't grab you, but I raced over 100 races in Triathlon and over 100 road bike races.
However holding those speeds is a different story.
THAT'S KPH.....mph is not used in bike racing except in USA.