3. Hair Pin Curves
• changes its direction through an angle of
180 or so, down the hill on the same side
• conforms to the shape of a hair-pin
• located on hill side having the minimum
slope
• must be safe from the view point of land
slides and ground water
• Hair-pin bends with long arms and farther
spacing are always preferred
4. Salient Curves
• The curves having their convexity on the outer edges of a hill road are
called salient curves.
• The center of curvature of a salient curve lies toward the hill side.
• This type of curve occurs in the road length constructed on the ridge of a
hill.
• The bend so formed at the salient curve in hill road is known as corner
bend.
• Salient curves are very dangerous for fast-moving traffic.
• At such a curve or at corner bend, the portion of projecting hill side is
usually cut down to improve the visibility.
• The outer edge of the road at such a curve is essentially provided with a
parapet wall for protection of the vehicles from falling down the hill
slope.
5. Re Entrant Curves
• The curves having their convexity on the
inner edge of a hill road are called re-
entrant curve.
• This type of curve occurs in the road length
constructed in the valley of a hill.
• These curves are less dangerous as they
provided adequate visibility to the fast-
moving traffic. At such curves, the parapet
wall is provided only for safety of fast-
moving traffic.
6.
7. Types of curves-
Vertical
• Summit Curve-
vertical curves with gradient
upwards.
• Valley Curve-
vertical curves with convexity
downwards
8. Summit Curves
• Objective :- To join 2 different
grades of roads with smooth
vertical curve, four different
conditions for formation summit
curve shown below –
9. Valley curve
• Objective – To join 2 different
grades of roads with smooth
vertical curve. Four different
conditions for formation summit
curve which are shown below -
10. Concepts behind
Summit Curve
• Design of summit curve on the basis
of sight distance.
• On summit curves, centrifugal force
acting outwards hence the springs of
vehicle is not compressed and
therefore passenger comfort is not a
issue.
• Design of summit curve as a square
parabola because the rate of change of
slope is decreasing always so more
sight distance available at the top of
curve.
Valley Curve
• In day time, no problem of any sight
distance but in night time head light
sight distance should be sufficient for
vehicle to stop before colliding with
object.
• In valley curves, the centrifugal force
will be acting downwards along with
the weight of the vehicle. This will
result in jerking of the vehicle and
cause discomfort to the passengers.
