Highway Engineering

If the object is assumed to have zero height (H 2 =0), then Equation 6.50 is
reduced to:

(6.64)

If the object is assumed to be at the driver’s eye height (H 1 =H 2 ):

LS=- 2 (6.65)

8H

A

1

LS=- 2

2H

A

1

LL==-S

()+ ()

m^12

2

2

2H H

A

see Equation 6.50

Geometric Alignment and Design 187

Example 6.8

A vertical crest curve on a single carriageway road with a design speed of

85 km/hr is to be built in order to join an ascending grade of 4% with a

descending grade of 2.5%. The motorist’s eye height is assumed to be 1.05 m

while the object height is assumed to be 0.26 m.

(1) Calculate the minimum curve length required in order to satisfy the

requirements of minimum sight stopping distance

(2) Recalculate the minimum curve length with the object height assumed

to be zero.

Solution (1)

p =+0.04

q =-0.025

From Table 6.7 the desirable minimum stopping distance is 160 m.

Since e >H 1 ,S£Las the sight distance is contained within the curve length.

Therefore, using Equation 6.49:

Solution (2)

If the object height is assumed to be zero, then Equation 6.49 reduces to

Equation 6.58:

L

S

m

2

12

2

2

2

A

2H 2H

0.065 160

2 1.05 2 0.26

= m

[]+

=

¥

[]¥+¥

= 353

eqp

8

0.025 0.04 160 8

1.3 m

=- -()=--()- ¥∏

=

L

Contd