Module 2: Road Design

Question 1

What is a station?

Answer 1

Horizontal distance along road (measured along centre line), with each station consisting of 1km
e.g. 1 + 234.56

Question 2

What is A?

Answer 2

A = || G1 - G2 ||

Question 3

What is the general form of equation of a vertical curve?

Answer 3

y = ax^2 + bx + c

Question 4

What is the value of ‘a’ in the general vertical curve formula?

Answer 4

a = (G2 - G1) / (2.L)

Question 5

What is the value of ‘b’ in the general vertical curve formula?

Answer 5

b = G1

Question 6

What is the offset formula for Yf?

Answer 6

Yf = AL/200

Question 7

What is the offset formula for ∆y?

Answer 7

∆y = GL/100

Question 8

What is the formula for Xhl and what does it represent?

Answer 8

Xhl = K . |G1|

Distance from PVC to the highest/lowest point

Question 9

What reaction time, grade and deceleration rate is SSD based off?

Answer 9

tr = 2.5 sec
G = 0
a = 3.4 m/s2

Question 10

When finding SSD, when should the assumption of G = 0 be used?

Answer 10

When G > 3 on a CREST curve

Question 11

What does K represent?

Answer 11

K is the horizontal distance required to cause a 1% change in slope

Question 12

What is the SSD of a sag curve governed by, and why?

Answer 12

Night time conditions, because the headlights govern what is visible to the driver

Question 13

What is the difference between R and Rv?

Hint: where are they measured to?

Answer 13

R: measured to centre of roadway
Rv: measured to centre of inner most lane

Question 14

When should Rv be used?

Answer 14

When considering SSD, vehicle design speed (V) and clearance distance (using Ms)

Question 15

What is the degree of curvature (equation & description)?

Answer 15

D = 5490/πR

Centre angle of arc of length 100ft (30.5m), provides measure of the ‘sharpness’ of curve