Exercise 1-A | Explanation's | Questions based on SSD | Highway Engineering

Important points:

• If reaction time (t) is not given assume t = 2.5sec (as per Indian Standard).
• Value of ‘ g’ always = 9.81
• Friction co-efficient for varuious design speed:

Speed =	<20	40	50	60	65	80	>100
f =	.40	.38	.37	.36	.36	.35	.35

• Breaking Distance for Downhill or down Grade = (-x%)
• Breaking Distance for Uphill or up grade = (+x%)
• SSD for various lane & way are given as below:

Type of traffic	1-lane, 1-way	1-way, 2-way	2-lane, 2-way
SSD required		2xSSD	SSD

Explanation for Exercise 1-A | Highway Engineering Numerical's | by Er. Neeraj Gosain 

QN 1. Calculate the Stopping Sight Distance for design speed of 60kmph for 2-lane, 2-way traffic.

Ans.       Given, Reaction time (t) = 2.5sec

                                g = 9.81

                                Speed = 60kmph or 60 x 1000  = 60/3.6 = 16.67m/sec  [∵reaction time is in seconds]

                                                                                 3600                     

                                ∵ SSD = vt +     v ²

                                                                                       2gf

                                ∴ SSD = (16.67x2.5) +       (16.67)                       

                                                                                   2x9.81xo.37      

                                                = 41.675m + 38.279m = 79.95~80m             

  

QN 2. Calculate minimum SSD to avoid had on collision of 2 cars approaching from opposite direction at a speed of 90kmph & 60kmph.

Ans.       Given,   t = 2.5sec

                                v = 90kmph or 90 x 1000/3600 = 90/3.6 = 25m/sec

                                v = 60kmph = 16.67m/sec

SSD_{1 =} (25x2.5) +         (25)²          

                                     (2x9.81x0.35)

                = 62.5+91.014 = 153.51m

SSD₂ = (16.67x2.5) +        (16.67)²              

                                                2x9.81x0.35

                = 41.675 + 40.467 = 82.14m

SSD_requuired = SSD₁+SSD₂

                               = 153.51+82.14 = 235.65m

                                                                                                                                                                                          QN 3. Calculate the SSD for design speed of 60kmph for single lane, 2-way traffic.

Ans.       Given,   t=2sec

                                v= 60kmph = 16.67m/sec

                SSD= (16.67x2)+     (16.67)²   

                                                        2x9.81x0.37

                                = 33.34+38.279 = 71.619~71.62m

                SSD_req= 2xSSD = 2x71.62 = 143.24m

                                                                                                                                                                                         QN 4. Calculate the SSD for desing speed of 60kmph for single lane, 2-way traffic.

            [assume b=80%]

Ans.       Given,   t= 2sec

                                v=60kmph = 16.67m/sec

                                b=80% (breaking efficiency)

                SSD= (16.67x2) +             (16.67)²          

                                                        2x9.81x0.37x0.8

∵SSD = vt +       (v)²           

                         2.gf.b

                                = 33.34 + 47.849 = 81.18m

            SSD_req. = 2x81.18 = 162.36m                                                                                                  

                                                                                                                                                                                        QN 5. Calculate the SSD for design speed of 60kmph for 2-lane, 2-way traffic of uphill moving vehicle gradient of 5% and breaking efficiency 80%.

Ans.       Given,   t=2sec

                                v=60kmph = 16.67m/sec

                                b= 80% = 0.8

                                x= 5% = +0.05

                SSD = (16.67x2) x                  (16.67)²                      

                                                        2x9.81x(0.37+0.05)x0.8

                SSD = 33.34+40.935 = 74.275m