E 544 Design Criteria

To preserve continuity of the street, the design criteria for all elements of the grade separation are the same as those used for major or secondary highways. Some of these basic requirements, covered elsewhere in this Part of the Manual, are also listed here as follows:

1. The same cross-section and width of the streets and highways concerned is carried on the approaches as well as on the underpass or overpass.
2. A design speed of 50 miles per hour should be used.
3. The geometric standards for horizontal and vertical alignment and for sight and stopping distances are the same as for major and secondary highways. Reference is made to the following:
   1. Section E 410, Horizontal Alignment.
   2. Section E 420, Vertical Alignment.
   3. Section E 430, Combination of Horizontal and Vertical Alignment.
   4. Section E 440, Sight Distance.
   5. Section E 610, Streets.
   6. Section E 650, Borders.
   7. Section E 540, Grade Separations.
4. Some railway bridges may be built with a clear span across the highway underpass.  The medians should generally be a minimum width of 10 feet and preferably 14 feet. An absolute minimum width of 8 feet may be used where a pier is required. Where a left turn lane is necessary, an absolute minimum width of 10 feet should be provided. The length of the storage should conform to standards previously covered. Where the median strip is at least 10 feet in width, landscaping may be considered. Reference is made to Section E 660, Medians.
5. Minimum vertical clearance is 15 feet between the soffit of the bridge and the pavement of the highway underpass, and 22.5 feet between the top of the rails and the soffit of the highway overpass at that point over the rails. Reference is made to Section E 320, Design Vehicle Physical Characteristics and Minimum Clearances.
6. The maximum desirable grade on the highway portion of the grade separation is 6 percent; absolute maximum is 7 percent. Only with prior special approval of the City Engineer should deviations from these standards be made.  Reference is made to Section E 331, Design Details.
7. The maximum grade break on centerline profile is 0.50 percent. Only with prior special approval of the City Engineer should any deviation from this standard be made. Reference is made to E 331, Design Details.
8. The maximum grade break at top of curb is 1.00 percent. Only with prior special approval of the City Engineer should any deviation from this standard be made.
9. The minimum grade of flow line at the curb is 0.250 percent.  Only with prior special approval of the City Engineer should any deviation from this standard be made. Reference is made to Section E 620, Pavements.
10. Parabolic crown section is to be used.  Only with prior special approval of the City Engineer should any deviation from this standard be made. Reference is made to Subsection E 621.1, Parabolic Crown Sections.
11. Side Slopes should have a maximum slope of 2:1. Only with prior special approval of the City Engineer should any deviation from this standard be made. Reference is made to Section E 680, Side Slopes.