Section 5: Vertical Alignment
Anchor: #i1086276Overview
The two basic elements of vertical alignment are Grades and Vertical Curves.
Anchor: #BGBJBFBHGrades
The effects of rate and length of grade are more pronounced on the operating characteristics of trucks than on passenger cars and thus may introduce undesirable speed differentials between the vehicle types. The term “critical length of grade” is used to indicate the maximum length of a specified ascending gradient upon which a loaded truck can operate without an unreasonable reduction in speed (commonly 10 mph [15 km/h]). Figure 2-5 shows the relationship of percent upgrade, length of grade, and truck speed reduction. Where critical length of grade is exceeded for two-lane highways, climbing lanes should be considered as discussed in the Highway Capacity Manual.
Figure 2-7. Critical Lengths of Grade for Design.
NOTE: Online users can click here to see this illustration in PDF format.
Table 2-9 summarizes the maximum grade controls in terms of design speed. Generally, maximum design grade should be used infrequently rather than as a value to be used in most cases. However, for certain cases such as urban freeways, a maximum value may be applied in blanket fashion on interchange and grade separated approaches.
|
(US Customary) |
|||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Functional Classification |
Type of Terrain |
15 |
20 |
25 |
30 |
35 |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
|
Urban and Suburban: |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
Local1 |
All |
<15 |
<15 |
<15 |
<15 |
<15 |
<15 |
<15 |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
|
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
Collector |
Level |
9 |
9 |
9 |
9 |
9 |
9 |
8 |
7 |
7 |
6 |
-- |
-- |
-- |
-- |
|
- |
Rolling |
12 |
12 |
12 |
11 |
10 |
10 |
9 |
8 |
8 |
7 |
-- |
-- |
-- |
-- |
|
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
Arterial |
Level |
-- |
-- |
-- |
8 |
7 |
7 |
6 |
6 |
5 |
5 |
-- |
-- |
-- |
-- |
|
- |
Rolling |
-- |
-- |
-- |
9 |
8 |
8 |
7 |
7 |
6 |
6 |
-- |
-- |
-- |
-- |
|
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
Freeway |
Level |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
4 |
4 |
3 |
3 |
3 |
3 |
3 |
|
- |
Rolling |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
5 |
5 |
4 |
4 |
4 |
4 |
4 |
|
Rural: |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
|
Local |
Level |
9 |
8 |
7 |
7 |
7 |
7 |
7 |
6 |
6 |
5 |
-- |
-- |
-- |
-- |
|
- |
Rolling |
12 |
11 |
11 |
10 |
10 |
10 |
9 |
8 |
7 |
6 |
-- |
-- |
-- |
-- |
|
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
- |
||