Capstone Design Topic: Transportation
Topic 1: After graduation, you started an engineering firm, and the first project is to design a two-lane highway in a rural area in California. The highway descends a hill, crosses under a bridge, and must shift to a parallel alignment on level terrain. You will design in paper the vertical alignment and horizontal alignment to meet design standards and minimize earthwork. Diagrams and other specifics are appended to the next page.
Topic 2: The City of San Francisco has experienced a disproportionate number of traffic fatalities involving elderly pedestrians. The Mayor hired your firm to conduct a safety study to identify risky locations across the City. You will present a report describing where collisions happened (through a Google map or other GIS maps) and what you have learned from site visits (via virtual site visits using Google Street Views). Bonus points will be given to teams that use innovative means to visualize or infer the data. Collision data are available at the San Francisco Department of Public Health Website: https://transbase.sfgov.org/dashboard/dashboard.php.
Additional Information for the highway design project:
Because of right-of-way reasons, the horizontal alignment must be straight until station 140 + 00. The transition to the new alignment must be completed within 3,000 ft., as shown in the Plan View.
The highway crosses a bridge at a right angle at station 120 + 00. The bottom of the bridge is 20 ft. above the soil. Note that AASHTO recommends a minimum structure clearance height of 14.5 ft. and a desirable clearance height of 16.5 ft. 1
The natural terrain is flat until station 100 + 00 where a downhill begins, as shown in the second diagram. Between stations 100 + 00 and 120 + 00, the soil elevation could be approximated by a Cosine curve, expressed as and x is the distance (measured horizontally) from station 100 + 00. This leads to an elevation of 7,100 ft. before the hill and an elevation of 7,000 ft. at station 120 + 00 and onward.
If you can, design the highway for safe travel at 65 mph; however, you may lower the design speed for short sections when necessary. You must indicate changes in design speed in your report.
If you use superelevation on your horizontal curves, there must be a straight transition section between the curves of 60 feet per 0.01 change in superelevation. For example, if one horizontal curve has e = 0.03 and the successive curve has e = 0.02, you would provide 300 feet of transition (because the two curves are banked in the opposite direction, creating a total change in superelevation of 0.05).
The average daily volume is 23,000 vehicles in each direction, with 90% of them passenger vehicles and 10% semi-tractor trailers.
For intersection sight distance, use single-unit truck as the design vehicle. The six-lane arterial is the major road, the two-lane highway is the minor road. Assume level grade on all intersection approaches.
Bonus point will be awarded to those designs that minimize the total cut and fill requirements for the vertical alignment. For simplicity, assume that you cannot move soil within the site, so the total cut and fill should be computed by taking the integral of the absolute value of the difference between the natural terrain and the proposed alignment. Use parabola for vertical curves and you
y = 7050 + 50cos(? x /2000)
Clearance height is the distance between the overpass structure and the roadway. Minimum curve length in the 1 presence of overpass structure is computed using the formulae on pages 3-162 and 3-163, Chapter 3 of the Green Book.
could use at most three vertical curves. Indicate all assumptions and reference all charts and equations used in the design process.
120+00
140+00
3,000 ft.
Highway centerline
Bridge
1,000 ft.
Natural terrain
Cross-section of the bridge
Station = 100 + 00; Elevation = 7,100 ft.
100 + 00
Plan View N
Natural Terrain
Station = 120 + 00; Elevation = 7,000 ft.
Elevation = 7050 + 50cos(?x/2000)
x 20 ft.
A
A
BB
C
C
