For your information:

For 0.8 s reaction time, driving at 30 m/s (108km/hr),  the car will move 30*0.8=24m before you hit the brake.
And the car will fully stopped after moving 30*30/(2*9.8*1)m,  about 45m.
(Police will you the length of the tire trace on the road to estimate the speed of the car).