Guide for the Development of Bicycle Facilities - The Industrialized ...

guide for development of bicycle facilities 37
On unpaved paths, where bicyclists tend to ride more slowly, a lower
design speed of 25 km/h (15 mph) can be used. Similarly, where the
grades or the prevailing winds dictate, a higher design speed of 40 km/h
(25 mph) can be used. Since bicycles have a higher tendency to skid on
unpaved surfaces, horizontal curvature design should take into account
lower coefficients of friction.
Horizontal Alignment
Unlike an automobile, a bicycle must be leaned while cornering to prevent
it from falling outward due to the generation of centrifugal force.
The balance of centrifugal force due to cornering, and the bicycle’s
downward force due to its weight, act through the bicycle/operator combined
center of mass and must intersect a line that connects the front and
rear tire contact points.
If bicyclists pedal through sharp turns and lean too far, the pedal will
strike the ground because of a sharp lean angle. Although pedal heights
are different for different makes of bikes, the pedal generally will strike
the ground when the lean angle reaches about 25 o . However, casual bicyclists
usually do not like to lean too drastically, and 15-20 o is
considered the maximum lean angle. Assuming an operator who sits
straight in the seat, a simple equation can determine the minimum radius
of curvature for any given lean angle:
For Metric Units:
R = 0.0079 V 2
tan θ
Where:
R = Minimum radius of
curvature (m)
V = Design Speed (km/h)
θ = Lean angle from the
vertical (degrees)
For English Units:
R = 0.067 V 2
tan θ
Where:
R = Minimum radius of
curvature (ft)
V = Design Speed (mph)
θ = Lean angle from the
vertical (degrees)
However, when the lean angle approaches 20 o , the minimum radius of
curvature negotiable by a bicycle becomes a function of the
superelevation rate of the pathway surface, the coefficient of friction between
the bicycle tires and the surface, and the speed of the bicycle. For
this situation, the minimum design radius of curvature can be derived
from the following formula:
For Metric Units:
For English Units:
2
2
V
V
R =
127 e
R =
⎛
⎜ +
⎝100 f ⎞
⎛
⎟
15⎜
e +
⎠
⎝100 f ⎞
⎟
⎠
Where:
Where:
R = Minimum radius of
= curvature (m)
R = Minimum radius of
= curvature (ft)
V = Design Speed (km/h)
V = Design Speed (mph)
e = Rate of bikeway
= superelevation (percent)
e = Rate of bikeway
= superelevation (percent)
f = Coefficient of friction f = Coefficient of friction
Design
Shared Use Paths