An equal-tangent sag curve has its PVI at station 10 + 00 and elevation at 138 ft. Directly above the PVI, the bottom of an overpass structure is at elevation 162 ft. The PVC is at station 4 + 00. If the initial grade is -4%, what is the highest possible value of the final grade given that a 70-mi/h design speed is to be provided in daytime conditions?
What is the highest possible final grade in nighttime conditions? (Note: Be careful of units of A, and ignore the cross-sectional width of the overpass.)