02-13-2009, 10:21 AM
Josh, don't worry about a grade being too steep for an on ramp or off ramp. Highway planners are not nearly as restricted as railroad engineers. 4.5% is considered too steep for mainline operation, although Cemex has a grade that steep between the quarry and the mill in Victorville. The "Grapevine" (I-5 between Gorman and Wheeler Ridge) has a 6% grade that is probably 6 miles long if I remember correctly. There is a 9% grade coming out of the town of Wrightwood West of Cajon Pass down Lone Pine Canyon. I think I have seen ramps as steep as 13%-14% in some of the hilly areas of Los Angeles County. I don't know what the grades are in San Francisco streets, but some like Davisidero look almost vertical.