Title: Horizontal Curves
1Horizontal Curves
2Highway Design Example
3Horizontal Curves
4Horizontal Curves Simple Curve
Straight road sections
5Horizontal Curves Compound Curve
Straight road sections
6Horizontal Curves Broken Back Curve
Straight road sections
7Horizontal Curves Reverse Curve
Straight road sections
8Horizontal Curves Spiral
Straight road section
9Geometry of Circular Curves
10Direction
11Geometry of Circular Curves
12(No Transcript)
13Geometry of Circular Curves
- Notation cont.
- I or ?
- E
- M
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15Geometry of Circular Curves
- Notable aspects of circle geometry
- Designation of Horizontal Curves
16Degree of Curvature
- Arc definition (Da)
- Central angle subtended by 100 feet of arc (along
curve)
- Note 100' ? one full station
17Degree of Curvature cont.
18Relationship of Da and R
- Metric equivalents by conversion, e.g.
19Curve Relationships
- Note
- Top five equations can be English or metric units
20Example Curve Calculations
- Given
- Deflection angle at PI (?) 8 24'
- Station of PI 64 27.64
- Da specified as 2 00'
- Compute
- Curve components
- Stations of PC and PT
21Derive Curve Components
22Derive Stations of PC and PT
- Station of PI 64 27.64
- Station of PC Station of PI T
- (64 27.64) (2 10.38) 62 17.08
- Station of PT Station of PC L (distance
along curve) - (62 17.08) (4 20.00) 66 17.08
23Selection (Design) of Curve
24Layout of Circular Curves
- Issue
- Angle-distance technique
- Note
25Sight Distance on Horizontal Curves
- Issue
- Standards
- Set by American Association of State Highway and
Transportation Officials (AASHTO)
26Example of Using SSD
- Consider
- Curve with R 1909.86 ft
- Sight obstruction (e.g. building) 12 ft from
curve (M 12 ft) - Question
- Recall car going 60 mph needs SSD of 475 ft
- Does curve have enough SSD for a car going 60 mph?
27LC ?
R 1909.86'
- Available sight distance 428' Required SSD60
475' - Not enough sight distance for 60 mph
- Post lower speed limit or redesign curve