49106: Road Engineering Practice Assessment Task 2 Brief

49106 Problem 1: Horizontal Alignment

A 4-lane road (2 lanes in each direction with no median separation) has a circular curve with a superelevation of 5% and a central angle of 50 degrees. The CT of the curve is at station 8+880 and the PI is at 8+806. The road has 3.6m lanes and 3.0m shoulders on both sides with high retaining walls going up immediately next to the shoulders (both sides of the road). 

Considering speeds in increments of 10km/hr (starting with 40km/hr), what is the maximum safe speed of this curve and what is the station of TC? 

49106 Problem 2: Vertical Alignment

A team of transport engineers have addressed safety concerns at a railway crossing on an existing level highway (Grade = 0) by proposing the construction of a highway overpass (above the existing railway line).

The following design constraints have been imposed:

• The existing highway has a design speed of 70km/hr
• Symmetrical vertical curves are designed for the overpass, the sag curves must be designed with a rate of vertical curvature of 23 (끫롼끫룀= 23) while the crest curves must be designed with a rate of vertical curvature of 17 (끫롼끫뢠= 17).
• The road surface of the overpass structure must be 7.5m above the existing highway.
• The overpass structure (bridge) must be level (Grade = 0), centred above the railway line and the length of the level bridge must be 60 metres.

Please answer the following questions.

1. Draw a clear labelled diagram presenting the overpass design described above.Clearly indicate the railway line, the vertical curve components, the bridge and indicate the dimension constraints described above.
2. Calculate the minimum length of the existing highway that must be reconstructed to provide the appropriate vertical alignment.

49106 Problem 3: Cross Section Design

A section of the Pacific Highway (2-Lane, 2-way) contains a spiral curve – circular curve – spiral curve which has been designed to connect two tangents of the horizontal alignment. The speed of this section of the highway is 80km/h. The following design principles are applied: 

• The superelevation at the circular curve is 5%,
• The normal crown has a cross-fall of 2.5%,
• The width of carriageway is 8.0m
• The length of the transition curve is 100m.

1. Calculate the cross-fall for the cross-section of the carriageway at a distance of 40mfrom TS
2. Present a drawing of the carriageway of the cross-section at a distance of 40m fromTS, showing the heights of the outside edge and inside edge of the carriage way relative to the centre line.

49106 Problem 4: Design of a Grade Separated Intersection

In the dynamic and expanding urban environment of “Slothsberg”, a new highway (“Snailpace Highway”) is to be constructed over the existing “Dillydally Highway”. The following conditions apply to the site:

• Snailpace Highway and Dillydally Highway intersect at right angles (90 degrees).
• As the highways are grade-separated (Snailpace Highway bridges over Dillydally Highway),there is a desirable clearance height of 5m between the two highways.
• Both highways are at a level grade (constant elevation).
• Snailpace Highway is oriented east-west at an elevation of 192m. The bridge structure is such that the bridge girder thickness is 2m (measured from the road surface to the bottomof the girder).
• A single-lane ramp is to be constructed to allow eastbound traffic to go southbound. Asingle horizontal curve, with a central angle of 90 degrees, is to be used (no transition curveis designed). The design speed for the curve is set at 70km/h and a required superelevationis 4%

Figure 1 and Figure 2 present diagrams of the alignment of the two highways. 

Figure 1: horizontal Alignment of Snailpace Highway and Dillydally Highway

Figure 2: Vertical Alignment of Snailpace Highway and Dillydally Highway

Using the Austroads Guide to Road Design Part 3: Geometric Design, determine the following features of the grade separated intersection design:

1. Stationing of TC, PI, CT, assuming the curve begins at station 3+321.000.
2. Stationing and elevations of all key points (PVC, PVI and PVT for each designedvertical curve) along the vertical alignment.
3. The distance that must be cleared from the inside of the horizontal curve so that theline of sight is sufficient to provide adequate stopping sight distance.