Overtaking sight distance and zone, 60 kmph

Data (IRC 66 / NRS 2070)

Speed of overtaking vehicle $V=60$ km/h, acceleration $a=0.79$ m/s², reaction time $t=2$ s. The speed of the overtaken vehicle is not given, so $V_b=V-16=44$ km/h (IRC), i.e. $v_b=44/3.6=12.22$ m/s. The opposing vehicle is taken at the design speed $V=60$ km/h.

(a) Safe overtaking sight distance

OSD = $d_1+d_2+d_3$.

• Distance in reaction time: $d_1=0.278V_bt=0.278(44)(2)=24.5$ m
• Minimum spacing ($v_b$ in m/s): $s=0.7v_b+6=0.7(12.22)+6=14.56$ m
• Overtaking time $T=\sqrt{\dfrac{4s}{a}}=\sqrt{\dfrac{4(14.56)}{0.79}}=8.58$ s
• Distance covered during overtaking: $d_2=0.278V_bT+2s=0.278(44)(8.58)+2(14.56)=134.1$ m
• Distance covered by the opposing vehicle: $d_3=0.278VT=0.278(60)(8.58)=143.2$ m

$$OSD=24.5+134.1+143.2=301.8\ \text{m}$$

OSD is about 302 m.

(b) Minimum length of overtaking zone

IRC recommends a minimum length of 3 × OSD = 3 × 302 = 906 m (desirable 5 × OSD = 1510 m).

(c) Sketch of overtaking zone

 Direction of travel  ---->
 [Sign: Overtaking zone]       [Sign: End of overtaking zone]
        |<----- Overtaking zone (min 3 x OSD) ----->|
 =======|===========================================|=======
 ------- - - - - - - - - - - - - - - - - - - - - - - -------
 =======|===========================================|=======
 continuous    broken centre line inside zone     continuous
 centre line                                      centre line
 (A "No overtaking" sign is placed beyond the end of the zone.
  The opposite direction has its own zone and signs.)

Signs are placed at the start and end of the zone (for each direction of travel). The centre line is a broken line inside the zone and a continuous line outside it.