Client
Transport for NSW
Picton Road provides an important link between the Illawarra Region and Sydney carrying a substantial volume of heavy vehicles (25%). TfNSW are at various stages of development for the proposed upgrade along this corridor between the Wilton Growth Area and the M1 Princes Motorway, including the interchange with the Hume Motorway.
CCHD were engaged in 2022 by TfNSW to develop a strategic design for upgrade of section 0 being the Picton Road / Princes Highway interchange and section 1 a total of 20km from the Picton Road / Princes Highway interchange to Macarthur Drive, south east of Wilton.
The existing Picton Road alignment traverses very challenging topography. There are several steep sections and many locations run along the ridge line that fall away once outside the existing carriageway footprint. Developing a dual lane upgrade to comply with increase in design speed and to current guidelines in combination with these topographical conditions’ present significant construction challenges, particularly where the roadway will remain under traffic throughout construction as is the case with the Picton Road corridor. This key constraint influenced the alignment and project footprint heavily. Some of the initial assumptions take into the design process to assist with constructability include:
- To assist with traffic switches during construction staging
- Ensure the proposed vertical alignment ties into existing carriageway levels where crossing of connecting
- Ensure existing posted speed is maintained throughout construction stages and traffic switches
- Ensure existing lane configuration (and therefore vehicle volumes) can be achieved on construction side-tracks and traffic switches.
To minimise impacts on the surrounding environment and major utilities, split level carriageways with retaining wall or one way slope in median have been adopted along several sections of the corridor to better “fit” with the exiting terrain.
A Safe Systems Approach has been adopted for this section of Picton Road due to the 110km/h design speed. This aims to remove right turn conflict via grade separation being a ramp and bridge over the main road and therefore avoiding the conflict point OR with a wide median U-Turn (WMU) which involves converting the side road to a left in/left out and therefore banning the right turn across the main road and provide a U-turn in the median at a downstream location to enable traffic to double back. The “downstream” location of the U-Turn is dependent on the number of lanes the entering vehicle must weave across before diverging into the U-Turn deceleration lane and traffic volumes to ensure this manoeuvre is achieved comfortably and safely.
Another consideration was futureproofing the cross section adopted where median width and location of retaining walls in the spilt level allows for a potential future widening to provide 3 lanes in each direction within the median.