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E. SIGHT DISTANCE The equations are based on a height of eye of 3.75 feet and a height of object of zero inches. A :rani- • To insure safe and of,Scent operation, bicycle mt:rn height of object is used here because such things facilities should be designed so that adequate sight disuace as gravel on a surface can be dangerous to a cyclst. is provided for safe stopping, on crestverncal carves and horizontal carves. Figure B gives sight distance values for various vertical carve lengths, algebraic differences in grade and 1. Safe Stopping Sight Distance speed. Design values for stopping sight distance may be 3. Sight Distance at Horizontal Curves computed in the same manner as for a highway.Generally, there is no problem in attaining adequate stopping sight Where a high embankment or wall is on the in- distances on bicycle lanes and shared roadways because the tide of a carve the sight distance for a bicyclist may not be roadway alignment usually has been designed to accorn. suffiaent. To check the horizontal sight distance for modate motor vehicle speed that are equal to or greater loicyclis-t, the bicycle has to be positioned 6 feet fur—her than bicycle speeds. There are exceptions, however,and the to the right than a motor vehicle. Figure C provides values stopping sight distance factor should be checked in lo- and formulas for sight distance on horizontal curves. caning such bicycle facilities. . STOPPING SIGHT DISTANCE F. WIDTHS AND CLEARANCES FOR DOWNHILL GRADES The surfaced or operating width required for a bike- Desiga Grade (%) way is one of the primary considerations of design. Speed 0% 5% 10% 15% mph feet I feet I feet 1 feet The min'—uum dissensions should include space re- 10 50 50 60 70 quired for the cyclist, allowance for lateral clearance to 15 85 90 100 130 obnacnons, and allowance for clearance to other hazards. 20 130 140 160 200 The typical bicycle and rider dimensions are given in 25 175 200 230 300 Figure D. In addition to the physical sr.-ace taken up by the � 30 230 260 310 400 bicycle and rider the following maneuver.:g allowances � 40 These values are based on a cxfricert of sicd res mance and clearances are generally accepted: • of 0.25, perception-reaction Cine of 2.5 seconds, height Desirable Distance of eye of 3.75 feet and an object height of 6 inches. The Type of Clearance feet height of an adult bicyclist's eye will normally be greater Maneuvering Allowance than 3.75 feet but a lower object may be pertinent. — handlebars to edge (for wobble) 1.0 — between bicycles(regardless of 2. Sight Distance at Crest Vertical Curves direction) 2.5 — between bicycles and pedestrians 2.5 In order to provide a better sense of alum-ay con- — between bicycles and motor tinuiry and riding quality, the use of vertical curves is vehicles 4.0(minimum) recommended where changes in grade are encountered. Sight distances at grade mesa can be checked using the Lateral Clearance (static obsnscdons) following equations: — parked cars 2.0 p s2 — curb drop-off 2.0 L - when S<L 750 — utility poles, trees, hydrants, fences, railings, etc. 2.0 — soft shoulders 1.5 L = 2S — --Q when S > L — sloped drop-off 1.0 A — raised curb 1.0 Where S = sight&stance in feet (based on design Vertical Clearances 8.5 (10' desirable) speed) L = length cf vertical curve (in feet) A = algebraic difference in grades in percent I . . 124