Design of Rural Road Segment

Topics: Orders of magnitude, Concrete, Road Pages: 13 (1501 words) Published: March 15, 2013

Design of rural road segment.

Table of contents

1.Scope of design exercise.3

2.Design data.3

3.Horizontal road alignment.3

3.1.Length of straight segments and angels of deflection.3

3.2.Horizontal curves.4
3.2.1.Calculation of curve length and tangent length.4

3.3.Road chainage.5

3.4.Determination of lane widening on curves.5

4.Vertical road alignment.6

4.1.Calculation of characteristic points on the road center line.6

4.2.Calculation of characteristic values of vertical curves.6

5.Road cross section.7

5.1.Road layers design.7
5.1.1.Results of computer simulation:8 vehicles per hour).8 (500 vehicles per hour).8 (5000 vehicles per hour).9

6.Transition curve.10

6.1.Finding parameter A.10
6.1.1.Geometry condition10
6.1.2.Dynamics condition10
6.1.3.Condition of road widening10
6.1.4.Aesthetics condition11
6.1.5.Condition of minimum circular curve shift.11
6.1.6.Condition of good curve proportions.11

6.2.Calculation of characteristic values for transition curve.11 6.2.1.Values read down from tables.11
6.2.2.Route shortening.12
6.2.3.Determining of chainage of new points.12

Scope of design exercise.

The objective of this project is to learn the detailed steps in geometric design of a rural 2-lane road of class Z.

The project exercise involves:

• designing the route in plan, including straight segments, circular and transition curves.

• designing the longitudinal profile, including tangent grades and vertical curves.

• designing the road cross-section, including pavement structural details.

Design data.

• Road design speed: 40[pic]

• Width of the bottom of drain:0.45 m

• Vertical distance from the drainage

layer outlet to the bottom of drain:0.70 m

• Contour line interval CI:1 m

Horizontal road alignment.

Designed road segment is composed of three straight segments and two curves.

1 Length of straight segments and angels of deflection.

Below are distances between points A, B, C and D, taken from the road map plan.

AB=380 m

BC=307 m

CD= 280 m

Two angles of deflection in points B and C were calculated, and are equal:


2 Horizontal curves.

Radius of horizontal curves was chosen according to following rules:

• Minimum distance between curves ends cannot be smaller than 100m

• Ratio of radius of second curve to radius of first curve should be not grater then 1.5 [pic]

• Greater the angel of deflection smaller the radius of curve.

Finally following radiuses were chosen:


Following super elevation of curve was chosen according to design speed:


1 Calculation of curve length and tangent length.

Curve 1



Curve 2



3 Road chainage.

• A = 0 m

• TC1 = AB - T1 = 380 - 64 = 316 m

• C1T = TC1 + L1 = 316 + 118.75 = 434.75 m

• TC2 = C1T + BC – T2 – T1 = 434.75 + 307 - 64 – 60 = 617.75 m

• C2T = TC2 + L2 = 617.75 + 108 = 725.75 m

• D = C2T – T2 + CD = 725.75 – 60 + 280 = 945.75 m

• Checking: D = AB + BC + CD – 2(T1 + T2) + L1 + L2;

945.75 = 380 + 307 + 280 – 2(64 + 60) + 118.75 + 108

4 Determination of lane widening on curves.

Curve 1:


Curve 2:


Vertical road alignment.

During designing of vertical road alignment one should take into account following rules:

• Slope of the straight segments should be bigger than 0.3% and shouldn’t exceed 8%.

• Distance between two curves should be greater than 250 m.

• Minimum radius of crest curve should be greater than 2500 m (for 60 km/h).

• Minimum radius of sag curve should be greater than...
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