Week Lecture 9-1
VERTICAL CURVE DESIGN (CONTINUED)
TOPICS General Controls for Vertical Alignment Alignment Coordination
Lecture 9-1. Geometric Highway Design Spring 2007
General Controls for Vertical Alignment
1. Use smooth gradeline and gradual changes. Use maximum grade and critical length of grade as criteria and apply carefully. 2. Avoid a roller-coaster or hidden-dip type of profile. 3. Substantial lengths of momentum grades should be evaluated for there affect on traffic operation (dont encourage excessive speeds). 4. Avoid broken-back gradelines, particularly in sags. 5. On long grades, place the steepest grades at the bottom and flatten the grade near the top. 6. Reduce the grade through at-grade intersections (reduces potential crashes) 7. Avoid sag curves in cut unless adequate drainage is provided.
Lecture 9-1. Geometric Highway Design Spring 2007
Harmonizing Horizontal and Vertical Curves
1. Horizontal curvature and grades should be in proper balance. Avoid the extremes of tangent alignment and steep grades or excessive curvature with flat grades. 2. Superimposing horizontal curvature on vertical curvature results in a more pleasing facility as long as some of the pitfalls are avoided. Sharp 3. horizontal curvature should not be introduced at or near the top of a pronounced crest vertical curve or at or near the bottom of a steep grade. 4. Designing long tangents at the expense of grade is appropriate where PSD is a over-riding consideration. 5. Horizontal and vertical curvature should be a flat a possible near intersections 6. Use separate designs for each direction of divided highways where practical. 7. Use depressed alignments to provide a noise buffer in residential areas where possible. 8. Enhance scenic views of the natural and man-made environment where possible
Lecture 9-1. Geometric Highway Design Spring 2007
Alignment Coordination
1. View in 3D where possible. 2. Use major controls to coordinate ...