Tiger Spider on VIC bridge access and PBS

Transport engineering consultancy, Tiger Spider, has ruminated on whether it is time to implement a new bridge formula in Victoria.

To get Performance-Based Standards (PBS) vehicles on the road in Victoria above the maximum 68.5 tonnes allowed on B-doubles, according to Tiger Spider, transport operators have had to wait months and pay large fees to VicRoads for bridge assessments every two years.

“If axle spacings between combinations differed by as little as 50mm, operators would be forced to wait and pay for re-assessments which can leave millions of dollars’ worth of new equipment sitting idle for months,” said Tiger Spider.

“To their credit, VicRoads have completed numerous ‘corridor studies’ to assess condition and costs and strengthen bridges on major arterial roads. They have published network maps based on Reference Vehicles which include various flavours of A-double, Quad-axle b-double and Quad-axle semi-trailer. The maps indicate whether bridges upgrades are funded and if so, expected completion dates.

“Road bridges are expensive to build and maintain and most are well beyond their nominal 50-year design life. It is easy to get frustrated with regulators and road managers, but they are tasked with managing a complex problem and progress is being made such that we now have a clear plan of action and network limitations are transparent to industry, politicians and the community.

“Progressively, bridges are being strengthened to new design standards which can easily handle the modern PBS fleet. The process of assessing bridge and providing networks now needs review to simplify access for operators and better align with adjoining states.

“From the beginning, PBS has applied a 3-Tiered bridge assessment process. Tier 1 is the bridge formula, the simplest method of compliance for operators, vehicle designers and road managers. Each PBS Level applies a different formula what has historically been allowed for general access, B-double and road train networks. Each bridge formula is a simple linear (straight line) equation where allowable mass across axle groups is related to their respective axle spacings.

“The level 1 bridge formula essentially allows 32 tonnes plus one tonne per metre up to 42.5 tonnes, Level 2 (B-double) allows 29.5 tonnes plus 1.5 tonnes per metre and Levels 3 (Type I road train) and Level 4 (Type II road train) allow 12.5 tonnes plus 3 tonnes per metre. Victoria has limited experience with the Level 3 (road train) formulas since until PBS, B-doubles were the heaviest vehicles allowed on Victoria roads (notwithstanding a small road train network in North Western Victoria).

“In contrast, all other mainland states have significant road train networks and therefore have experience applying the PBS Tier 1 Level 3 bridge formula. Now that Victoria has essentially approved 36.5 m (PBS Level 3A) on 80 per cent of the arterial road network, it’s time they developed a clear goal of developing a Level 3 PBS network map and provided access based on the Level 3 bridge formula.

“Whilst the bridge formula is not new, it’s important that it is adapted to ensure it accounts for heavier steer axles and quad-axle groups. Therefore, the level 3 formula (M >= 3L + 12.5) should include 24 tonnes GML for quad-axles (27 tonnes HML), steer axles up to 7.1 tonnes and twin steer axle groups at up to 12 tonnes.

“Implementing a new simplified bridge formula will unlock massive transport productivity gains and provide a pathway for national consistency.

“However, a bridge formula is not a silver bullet and road managers still need to continue to invest in intelligent automated bridge assessment tools which will optimise network and gross mass for a given vehicle combination. Australian state road managers have done this for many years, but Tasmania now leads the way by providing an open system which can be used by vehicle operators to automate bespoke networks for special purpose vehicles.

“In time, this will become available for PBS vehicles as well. Importantly, road managers need to continually focus on strengthening bridge and ensuring that we have a modern road system which ensures our primary producers are internationally competitive.”

In other news, Tiger Spider outlines why PBS is the best option for higher productivity.