Division 13-10-008
Vertical Alignment
Sections:
13-10-008-0001 Vertical Alignment
13-10-008-0002 Other Design Considerations
13-10-008-0001 Vertical Alignment
The street plan of a proposed subdivision shall bear a logical relationship to the topography of the property. All streets shall be arranged to allow most of the building sites to be at or above the grade of the streets. Vertical alignments are controlled to assure that the street grades can be negotiated in adverse weather conditions and that sight distances are adequate for safety. Sufficient data shall be given on each curb line or edge of paving and on the crown of paving so that the elevation of any point may be mathematically calculated. Grade or slopes on curved streets shall be computed and recorded for the true length of curbing as measured at the back of curb. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-10-008-0002 Other Design Considerations
Other design considerations shall be based as follows:
A. Grades. Maximum grade for any street varies from six percent (6%) to ten percent (10%) depending on street classification (Table 13-10-008-01). Minimum flow line tangent grades shall be four-tenths percent (0.4%) (the preferred minimum is five-tenths percent (0.5%)).
B. Maximum grades around curb returns at intersections or on the inside curb on horizontal curves shall not exceed the maximum allowed centerline grade for that functional classification of street by more than two percent (2%).
C. Vertical Curves. All straight grades that deflect by more than one percent (1%) must be joined by a parabolic vertical curve. The length shall be determined using the current AASHTO "Policy on Geometric Design of Highways and Streets." The minimum vertical curve length for a given design speed is determined in Table 13-10-008-01 as the greater of the value in the ‘Minimum Length’ column or the length calculated from the ‘Rate of Vertical Curvature’ column by the formula:
L = K x A (where: L = minimum curve length (ft.)
K = rate of vertical curvature (ft./%)
A = algebraic difference in grades (%)
|
MINIMUM VERTICAL CURVE LENGTH |
|||
|---|---|---|---|
|
DESIGN SPEED |
MINIMUM LENGTH |
RATE OF VERTICAL CURVATURE K (ft. per % grade change) |
|
|
mph |
ft. |
CREST |
SAG |
|
20 |
60 |
7 |
17 |
|
25 |
75 |
12 |
26 |
|
30 |
90 |
19 |
37 |
|
35 |
105 |
29 |
49 |
|
40 |
120 |
44 |
64 |
|
45 |
135 |
61 |
79 |
|
50 |
150 |
84 |
96 |
Vertical curve data recorded shall include the length, P.I. elevation, correction factor or finished grade at the mid-point of the curve, and elevations at twenty-five (25) foot stations.
D. Curb Returns. Data shall be given which will include curb elevations at one-half (1/2) delta, (one-quarter (1/4) delta preferred) around the return, tangent slopes, P.I. elevations, and other related features.
E. Benchmark. Permanent benchmarks shall be established in projects having no benchmark in the immediate area in accordance with Section 13-03-003-0003. (Ord. 2017-22, Rep&ReEn, 07/05/2017)