[Ref faa.gov]

One common and misleading way to think of V1 is to say “V1 is the decision speed.” This is misleading because V1 is not the point to begin making theo perational Go/NoGodecision. The decision must have been made by the time the airplane reaches V1 or the pilot will not have initiated the RTO procedure at V1. Therefore, by definition, the airplane will be traveling at a speed higher than V1 when stopping action is initiated, and if the airplane is at a Field Length Limit Weight, an overrun is virtually assured.

p.S through reading this material, a good site is discovered: https://www.faa.gov/other_visit/aviation_industry/airline_operators/training/