Many of the principles and guidelines that the civil engineers who design Australia’s roads work from are the result of research conducted in Queensland close to 20 years ago.
Of the innovations introduced over that time, one of the more significant has been extended design domain (EDD).
As laid out in the Austroads Guide to Road Design, EDD provides a framework for practitioners to navigate work outside normal road design parameters, yet still ensuring the resulting infrastructure is safe, sustainable and suitable for purpose.
“Normal design domain is applied to green-field sites: a brand-new area with no design constraints,” explained Professor Dennis Walsh, Chief Engineer at Queensland’s Department of Transport and Main Roads (TMR).
“EDD options came about from research that examined what happens when you don’t have a perfect site. What are some levers you can pull as an engineer, using judgement and common sense and research, to get the best result possible out of a particular site?”
EDD options provide design criteria for the times when practitioners have to step outside the regular rules. And having been applied practically for two decades, there’s plenty of evidence that they do exactly what they’re designed to do: permit engineers to use their creativity and expertise to find solutions that accommodate the complexities of modern projects.
“For example, if an engineer designs a curve in the road to be tighter than normal, there’s a chance the vehicle could lose control as it goes around it,” Professor Walsh said.
“But if the landscape gives the engineer no choice, they could gather documentation and weigh the benefits of departing from the standard design with the risks associated with an EDD, then present the alternative option to the asset owner. Because it’s outside the normal design domain, the process is heavily documented to protect the public, as well as the engineer and the asset owner.”
The EDD concept has matured to become an established practice – an efficient and effective way of approaching practical design challenges – and many engineers have become comfortable with its use and are confident in its outcomes.
On the other hand, there are some engineers who are not as comfortable or find the documentation too onerous to make EDD adoption worthwhile.
“It’s to the point where we are finding too many engineers are applying normal design domain even though it’s more expensive to the taxpayer where extended design domain would be accepted by the asset owner,” Professor Walsh said.
Taking the hurdles away
In response, TMR is improving its processes in Queensland by increasing efficiency in EDD documentation and reporting. The EDD parameters themselves will not change, but less effort will be needed to apply them.
Since EDD is an approach rooted in common sense, Professor Walsh said TMR wants to similarly apply common sense to how and why it requires documentation when an engineer applies EDD.
After all, Queensland has a strong history of successfully implementing EDD solutions for road design, and the state’s extensive experience has demonstrated that it can be applied without affecting the safety of road users.
“This is where we’re trying to take the hurdles away,” Professor Walsh said.
“We are saying as an asset owner, we’re comfortable with minimising the reporting in situations that use tried and tested deviations from normal.”
“In situations where EDD has been applied and there haven’t been any adverse impacts, we’re willing to accept it without 100 pages of documentation. The engineer, as a responsible practitioner, should do what they need to do to be satisfied that the EDD is okay to be signed off.”
“We are hoping this change will encourage greater application of EED by engineers. We will review the impact of this change and consider any other strategies which may be necessary to drive better value outcomes while not compromising safety.”
Pragmatic solutions
EDD is for extensions beyond standard practice, but that doesn’t mean its use is exceptional. There are plenty of situations where it is simply the most straightforward solution to a particular design challenge.
Roads in urban areas, for instance, might need to be designed with narrower lane widths than standard. Some crest curves are built slightly tighter than usual because the alternative is cutting hundreds of metres of earth longitudinally out of a mountain.
“All of the EDD options that are available have been used to some extent all over our network already; that’s why we’re so comfortable with them,” Professor Walsh said.
And streamlining all EDD processes in Queensland has foreseeable benefits, particularly considering the amount of infrastructure the state will need to build as the 2032 Brisbane Olympic Games get nearer.
“You potentially get more innovation happening on projects where practitioners are willing to apply EDD,” Professor Walsh said.
“We will get more pragmatic solutions and cheaper, more efficient projects.”
