# Civil Engineering - GATE Exam Questions - Discussion

Discussion Forum : GATE Exam Questions - Section 1 (Q.No. 4)
4.
On sag (or valley) curves the available sight distance is determined based on :
design speed
height of obstacle
height of driver eye
night-time driving conditions
Explanation:
No answer description is available. Let's discuss.
Discussion:
34 comments Page 1 of 4.

Ismail said:   7 years ago
The valley curve should be designed such that there is enough headlight sight distance. Improperly designed valley curves result in extreme riding discomfort as well as accident risks, especially at nights. The length of valley curve for various cases was also explained in the section. The concept of Valley curve is used in underpasses.

Jyoti chaudhary said:   8 years ago
In valley curves two conditions are required-comfort zone (in which the change in centrifugal acceleration is limited upto a certain level).

Safety criteria: In which the driver should have adequate light during night.

So option (D) is correct.

Naveen said:   8 months ago
Night-time driving condition is the correct answer as the headlight of the vehicle at night is blocked by the vertical curve of the sag curve so that's why a beam angle of 1 degree is provided to get the desired headlight sight distance.

M.suna said:   7 years ago
Answer c should be correct. Because according to the relation L= NS2/2h+2stan (α).

Alpha should be always 1 as per IRC. So hear, if we find out "h" i.e. height of the driver then we can get SSD easily.

Sneha Mathai said:   3 years ago
In a valley or sag curve, the design is based on headlight sight distance only. It is because night time driving is to be taken at almost care in valley curves.
(1)

Ahsen said:   4 years ago
Should it not be option D?

As there are no visual restrictions on sag curve and the only concern remaining is the glare due to vehicle headlight at night time.

Chanti said:   6 years ago
In summit (hog) curves available sight sight distance is based on SSD.

In valley (sag) curves available sight distance is based on head light distance.

Kunjita dashore said:   7 years ago
Option D is correct. On the basis of night Time driving conditions on valley curve available sight distance is determined.

Sagar said:   7 years ago
Sight distance depends upon height of the headlight i.e. 0.75m in turn is used only in nighttime driving condition.

Nishit said:   9 years ago
Because driver can see the obstacles or vehicle which moves at either side of curvature & reduce the accident.