Vertical Alignment of Highway Roads | Gradients for roads in different terrains | Length of Summit Curve (L) | Length of Valley Curve (L)
Vertical Alignment of Highway Roads | Gradients for roads in different terrains | Length of Summit Curve (L) | Length of Valley Curve (L)
INTRODUCTION :
Vertical Alignment of Highway Roads:
The vertical alignment of highway generally defined as the presence of heights and depths in vertical axis with respect to horizontal axis of alignment. These heights and depths in roads may be in the form of gradients (straight lines in a vertical plane) or vertical curves.
1.Gradient;
Table ; Gradients for roads in different
terrains
|
Type of terrain |
Ruling gradient |
Limiting gradient |
Exceptional gradient |
|
Plain or Rolling |
3.3
% (1 in 30) |
5.0
% (1 in 20) |
6.7 % (1 in 15) |
|
Mountainous terrain and steep terrain having elevation more than
3000 m above
MSL |
5.0 %
(1 in 20) |
6.0 %
(1 in 16.7) |
7.0 %
(1 in 14.3) |
|
steep terrain up to 3000 m height above MSL |
6.0
% (1 in 16.7) |
7.0 % (1 in 14.3) |
8.0 % (1 in 12.5) |
|
N |
= |
Deviation angle (algebraic difference in grades) |
|
S |
= |
Sight Distance (m) (either SSD or OSD or ISD) |
|
H |
= |
Height of eye
level of driver
above roadway surface
(m) |
|
â„Ž Note: |
= |
Height of subject above roadway surface (m) |
For SSD H = 1.20 n and â„Ž = 0.15 n â„Žence (√2H + √2â„Ž) ^2 = 4.4 n
For OSD or ISD H = 1.20 n and â„Ž = 1.20 n â„Žence (√2H + √2â„Ž)^2 = 9.6 n
3.Length of Valley Curve (L):
A.
Comfort Condition
B. Head
Light Sight Distance
|
N |
= |
Deviation angle (algebraic difference in grades) |
|
S |
= |
Head light sight Distance (m) (HSD = SSD) |
|
â„Ž1 |
= |
Height of head
lights above roadway surface (m) |
|
α |
= |
Inclination of head light beam with horizontal |
Note: ℎ1 = 0.75 n and α = 1o ℎence (2ℎ1 + 2S tan α) = (1.5 + 0.035 S)
COMMENTS