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<br />various traffic volumes and design speeds. Graded <br />shoulder width is measured from the edge of surfacing <br />(pavement) to the point of intersection of shoulder <br />slope and side slope. In mountainous terrain, with a <br />minimum two-foot shoulder, the graded width of shoulder <br />in cuts may be decreased 2 feet if guardrail is <br />installed. Guardrail shall not be closer than 2 feet <br />from the driving surface. <br />The minimum roadway width is the direct sum of the <br />surfacing and graded shoulder widths shown below. <br />Lanes shall be at least 11 feet wide and shoulders 2 <br />feet wider than the minimum shown below. <br />Width of Surfacincr and Graded Shoulder fFeetl for Design Volume <br />of: <br />Design 0- 25- 250- 700- 1000- 2500- <br />Speed fmoh) 25 250 600 1000 2500 4400 4400+ <br />Width of Driving Surface (FeetZ <br />15 16 -- -- -- -- -- -- <br />20 16 22 22 24 24 24 24 <br />30 16 22 22 24 24 24 24 <br />40 -- Z4 24 24 24 24 24 <br />" '`; 50 -- 24 24 24 24 24 24 <br />yi <br /> Width of Shoulder (Feet) <br />A11 Speeds -- 2 - 2 - 4 - 6 - 6 - 8 <br />2 4 6 6 8 8 <br />5-502 T. Switchbacks <br />Switchbacks are not considered a good roadway design <br />solution for gaining elevation, especially on hillsides <br />steeper than 20 percent where switchbacks produce <br />visual heavy impact. No switchback shall have a <br />tangent less than ~;-mile from the last switchback. <br />Grades on switchbacks shall be reduced to zero at the <br />apex of the vertical curve on horizontal curves less <br />than 150 feet, and the horizontal curve shall not begin <br />prior to the end of the vertical curve for these <br />purposes. <br />5-502 U. Vertical Clearance <br />Vertical clearance at underpasses, powerlines, street <br />lights, etc., shall be at least 15 feet over the entire <br />roadway width. <br />Page 5-5-13 <br />