2Design philosophy for temporary roads#

In considering design parameters outside of NDD and EDD parameters for temporary road alignments, there are a number of overall considerations that should be incorporated into the design. Main Roads WA identifies that all temporary alignments should have the following primary design objectives:

• Maximise safety for both the road users and road construction workers.
• Minimise costs associated with construction, maintenance and use of the route.
• Consider the planned ultimate layout (road and adjacent developments) in the vicinity of the works and ensure that it can be accommodated with a minimum of reconstruction in the future.
• Maximise operational efficiency, that is the ability to carry the required volume of traffic at a speed acceptable to the road user.
• Maximise opportunities to cater for the needs of all road user groups.

The National Cooperative Highway Research Program Report 581 - Design of Construction Work Zones on High-Speed Highways (NCHRP 581) identifies that:

The key elements considered relevant to the design of temporary roads as detailed in NCHRP581 include:

• Typically for temporary roads it is recognised that the feasible range of design alternatives is often constrained by cost and site constraints such as right-of-way and environmental features. Designs for temporary roads are often more restricted than designs for permanent roadways, since the work site must also accommodate construction operations and be closely aligned with the permanent road.

• Safety – a focus should be retained on achieving “substantive safety” recognising that temporary works result in a different level of exposure compared to a permanent design. As roadworks exist only for a finite period of time, it is therefore appropriate to consider exposure differently. A specific condition may exist for a period ranging from hours to years, but not indefinitely. For construction sites, exposure can be characterised by accounting for both exposure (e.g., AADT) and duration. Conditions that may not be acceptable indefinitely (i.e., as part of a permanent roadway) may be acceptable for a low level of exposure (i.e., for a short duration and low traffic volume).
• Design Consistency – should apply in the development of temporary road designs so the prevailing driver expectations are reinforced. Hence to design a temporary alignment in such a way that the experience aligns with a drivers expectation for a higher speed limit, it may be difficult to achieve a speed compliance with a lower temporary limit if the design cues do not reflect a reduction in design standard.
• Primacy – ensuring that drivers recognise and respond appropriately to the site features. Safety-critical and other important information should be clearly, conspicuously, and prominently presented to drivers.
• Speed Management and Design Speed – including the need to establish reasonable temporary speed limits, and the need to employ the appropriate measures to attain speed reduction through measures that are self-enforcing.
• Forgiving roadside.