Question

A non-equal tangent curve has L1=20 stations, G1=-1%, L2=30 stations, G2=+2%. What is the grade from the intermediate PI on the incoming tangent to the intermediate PI on the outgoing tangent?

Answer 1

Given for unequal tangent curve,

G1= -1%

G2= +2%

L1= 20 stations

L2= 30 stations

Taking 100 ft= 1station

L1= Length of first tangent of unequal curve = 20 *100 = 2000 ft

L2= Length of second tangent of unequal curve = 30 *100 = 3000 ft

So, length of PI1= 2000/2 =1000 ft

Length of PI2 = 3000/2 = 1500 ft

Assume, the elevation of intermediate PI = y ft

Elevation of PI1 = y + (1000*1)/100 = (y+10) ft

Elevation of PI2 = y + (1500*2)/100= (y+30) ft

Grade = ((y+30)-(y+10)) * 100 / (1000+1500) = 0.8 %