For an adult human in good shape, I'll be honest: not very fast.
13 mph
From 10 to 40 mph
9.6 sec that's how fast i can run a 40 dash
13.5 mph
80.25 yards
about 40 mph
If the peacock is in very grave danger it will do 100 yards, peace of cake and can reach speeds up to 40-50 mph. That would be very rare, but I garantee you I have seen this happen with my own eyes back in India!
A good rule of thumb is to keep a distance of one car length, about 10 feet, for every 10 mph of speed, so at 40 mph, you should be 40 feet behind the car in front of you. Obviously, this is harder to do in heavy traffic.
22.7 mph
40 mph
up to 45 mph
Running 40 yards in 4.2 seconds is equal to running 19.5 MPH.