Highway Engineering

 The driver’s eye height H 1


 The height of the object on the highway H 2


 Minimum curve length Lm.

In order to estimate the minimum curve length, Lm,ofa crest curve, two con-

ditions must be considered. The first, illustrated in Fig. 6.20, is where the

required sight distance is contained within the crest curve length (S£L), while

the second (see Fig. 6.21) entails the sight distance extending into the tangents

either side of the parabolic crest curve (S>L).

The formulae relating to these two conditions are:

(6.49)

LSLm^12 (6.50)

2

2S

2H H

A

=- for

[]+

()>

L

S

m SL

2

12

A

2H 2H

= for

[]+

2 ()£

184 Highway Engineering

Balanced highway with fall from

centre-line towards both edges

Centre-line

2.5% 2.5%

2.5%

Highway with crossfall from one edge

to the other Figure 6.19crossfalls. Highway

D 1 D 2

H 1 H 2

S

L

e

e

pq

Figure 6.20Case (1) S£L.