Highway Engineering

(6.58)

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

(6.59)

Case (2) S >L

Referring to Fig. 6.21, if we assume that g is equal to the difference between the

slope of the sight line and the slope of the rising straight-line gradient, p, then

the sight distance Scan be estimated as follows:

S (6.60)

L

=+ +

2 -

H

g

H

Ag

12

L=AS

8H

2

1

L=AS

2H

2

1

186 Highway Engineering

Figure 6.21Case (2) S>L.

In order to derive the minimum sight distance Smin,Sis differentiated with

respect to g as follows:

(6.61)

Therefore:

(6.62)

Substituting Equation 6.62 into Equation 6.60:

(6.63)

Bringing Lover to the left-hand side of the equation:

S=+ ∏L -

-

È

ÎÍ

̆

̊ ̇

Ï

Ì

Ó

̧

̋

̨

+∏- -

-

È

ÎÍ

̆

̊ ̇

Ï

Ì

Ó

̧

̋

(^2) ̨

H AHH HA

HH

HAAHH HA

(^1) HH
12 1
21
2
12 1
21
g AHH HA
HH
12 1
21

= -

-

d

dg

H

g

H

A g

21 2 2 0

S

=- +

()-

=