Highway Engineering

A, H 1 ,H 2 and Sare as above.

Case (2) S >L

LSm 2 8C1 H^12 H /2 (6.68)

A

=- -+

[]()

190 Highway Engineering

Example 6.10

A highway with a design speed of 100 km/hr is designed with a sag curve

connecting a descending gradient of 3% with an ascending gradient of

5%.

(1) If comfort is the primary design criterion, assuming a vertical radial

acceleration of 0.3 m/s^2 , calculate the required length of the sag curve

(comfort criterion).

(2) If a bridge structure were to be located within the sag curve, with a

required clearance height of 5.7 m, then assuming a driver’s eye height

of 2 m and an object height of 0.26 m, calculate the required length of

the sag curve (clearance criterion).

Solution (1)

Solution (2)

The design speed of 100 km/hr gives a desired sight stopping distance of

215 m

Since e >H 1 ,S<Las the sight distance lies outside the curve length.

Thus, utilising Equation 6.67:

L

S

m

2

12

2

A

8C1 H H /2

0.08 215

8 5.7 2.0 0.26 /2

101 m

=

[]-+()

=

¥

[]-+()

=

eqp

8

0.05 0.03 215 8

2.15 m, which is greater than the driver’s eye height of 2 m

=- -()=--()- ¥∏

=

L

L

V

==

¥

=

(^22) A
3.9

100 0.08

3.9

205 m