Speed of overtaking vehicle,
V=80 kmph=22.22m/sec
Speed of overtaken vehicle,
Vb=50 kmph=13.89 m/sec
Average acceleration during overtaking,
a=0.95 m/sec2
Overtaking sight distance for two ways traffic,
OSD=d1+d2+d3
=(Vbt+Vb+2S+VT)
d1=Vbt=13.89×2.5=34.7 m
d2=VbT+2S
S=0.7Vb+6=0.7×13.89+6=15.723 m
T=√4Sa=√4×15.7230.95=8.136 sec
d2=13.89×8.136+2×15.723=144.5 m
d3=VT=22.22×8.136=180.8 m
OSD=d1+d2+d3=34.7+144.5+180.8=360 m
Now, minimum length overtaking zone
=3×OSD=3×360=1080 m
Also, desirable length of overtaking zone
=5×OSD=5×360=1800 m