Wk 3 Flashcards
what requirements are considered when roads are designed ? (4)
- Passenger Comfort:
This is based on an empirical formula derived during the days of early railway construction
- Safety:
Based on sight distances and safe stopping distances
- Forces on the car:
The use of superelevation and/or transition curves to introduce centrifugal force in a controlled manner
- Drainage :
Road surface can be considered to slope in two directions β longitudinally, in the direction of the centreline of the road, and transversely, at right angles to the centreline of the road
equation for the min radius of a simple curve
+units
whatβs the purpose of superelevation?
The purpose of employing superelevation of the roadway cross-section is to:
counterbalance the centrifugal force, or outward pull, of a vehicle traversing a horizontal curve.
Side friction developed between the tyres and the road surface also counterbalances the outward pull of the vehicle.
define (give what it is in terms of reference + formula):
theta
Tangent length
π is the deflection angle
TANGENT LENGTH: TP1 β IP and IP β TP2
πππππππ‘ πππππ‘β = π
tan(π/2)
Define long chord
LONG CHORD: ππ1 π‘π ππ2 = 2π π ππ(π/2)
Define arc length
ππ1 π‘π ππ2 = π π (in radians)
π ππ/180 (in degrees)
define Tangent Angle between two
subsequent pegs
define chainage
measure of the length from the starting point of the scheme to the particular point in question and is used in road, as a means of referencing any point on the centre line.
calculate:
- tangent length
- length of the curve
Find the tangent points (CH TP1, CH TP2)
What is the chainage of the first peg at 25m of
through chainage on the curve?
main function of vertical curve design of road
One of their main functions is to ensure that passengers in vehicles travelling along the curves
are transported safely and comfortably
used to design roads in the vertical direction on
undulating ground at the intersection of differing gradients
In terms of gradients what does 1 in 20 mean?
go up 1m for every 20m travelled horizontally
what would a 5% increase and 5% decrease in gradient look like? (express in vertical curves)
what is G (terms of vertical curve)
G is the Gradient angle or the difference in slope
πΊ = ππππ π‘ π ππππ β π πππππ π πππe
Find the G for:
i
ii
And state whether its convex or concave
i Convex
ii convex
Find the G for:
i
ii
And state whether its convex or concave
what curves are used in vertical curve design? and why
Parabolic curves are used in vertical curve design as this gives a constant rate of change of gradient
What types of horizontal curves are there
βSimple curve
βCompound curve
βReverse Curve
βSpiral Curve
