Busting the myths on truck width and road safety

Are wider trucks going to be less safe? Categorically, no. While Australia eagerly awaits a decision by Federal transport ministers on reforms to Australia’s overall truck width limits, there has been some public commentary around the possible negative impacts of those increases, none of which have any merit.

This edition of ‘The Tech’s Files’ unpacks the proposal to increase width using facts and published research, and looks at why the reform is critically important for the local Australian industry.

The width situation

Increases to overall width limits for trucks have a long history, but only two recent developments are relevant.

At the May 2018 meeting of the then Transport and Infrastructure Council, Ministers endorsed the National Road Safety Action Plan of 2018-2020, which included a commitment to investigate the introduction of safer, cleaner trucks by minimising regulatory barriers.

In April 2021, the Federal Department of Infrastructure released its ‘Safer Freight Vehicles’ (SFV) Discussion Paper, which proposed possible changes to Australian Design Rules to achieve the goals of that action plan. One of those changes was to increase width.

How does increasing width make vehicles safer and cleaner? The answer to that question lies beyond our shores.

Australia’s truck width limit is 2.50 metres (excluding rear vision mirrors, signalling devices, lamps, tyre inflation systems, and some load restraint equipment). In the European Union, the limit is slightly greater at 2.55 metres. In the USA, trucks can be wider still, up to a maximum of 2.60 metres.

Are wider trucks going to be less safe? No. (Image source: Austroads)

These different limits mean that vehicles imported into Australia from markets with greater limits must be re-designed (or modified) at significant cost to the vehicle manufacturer. That cost was estimated in 2021 at between $15 and $30 Million dollars, across the industry.

This is an impediment that slows the introduction of safer, cleaner vehicles into the Australian market, and in some cases, presents enough of a barrier to prevent their introduction entirely.

HVIA’s policy position

HVIA’s position on truck width has been clear since 2019, and strongly articulated to all levels of government – the current truck width limit of 2.50 metres restricts model availability and adds unnecessary costs to the industry. The industry needs an increase to at least 2.55 metres.

What about trailers? A different set of operating conditions apply, which means that a different approach is needed. Australia’s current width limit for trailers is also 2.50 metres (with the same exclusions that apply to trucks, as noted above), but that limit does not restrict the fitment of safety nor environmental technologies, it does not substantially limit productivity and also does not add cost to the industry.

Conversely, an increase to trailer width limits would require local manufacturers to re-tool their production facilities. The drawbacks combined with a lack of clear benefits led HVIA to advocate for a Regulatory Impact Statement (RIS) including a segment-by-segment trailer market analysis, and outright avoidance of an across-the-board increase to the trailer width limit.

Busting the myths

Most of the commentary circulating focuses on the way that wider trucks may interact with existing road infrastructure. Some claim that roads aren’t built to accommodate wider trucks, infrastructure upgrades are needed, a standardised road width may eventually be required, and that longer vehicle combinations (such as B-doubles) that are also wider should only be allowed access to specific routes.

Does any of that have merit? No. Let’s look at why, starting with road widths. Australian road design guidelines for lane width are comparable to those in the EU, UK and the USA, where vehicles are permitted to be up to 2.55 metres and 2.60 metres wide, respectively. So while the current Australian road infrastructure network was built under a different truck width limit, it is by no measure deficient.

Do wider trucks take up more space? The difference is negligible. When driving in a straight line, a truck and trailer combination will require slightly more clear area within a lane than its overall width. This is due to the shape of the road surface, which is often ‘crowned’ (i.e. raised at the centreline, and sloped at the edges) to ensure water runoff. That shape tends to ‘drag’ the rear trailers downwards towards the edge of the road, and can be exacerbated by the roughness of the road.

How road shape and roughness impact road space requirements (Image source: ARTSA)

This characteristic is already captured in road design requirements, and increasing the width of trucks by 25 millimetres on each side will have a negligible impact. A minuscule number of narrow roads in urban or built-up areas may require signposted access restrictions but are unlikely to have been suitable for 2.50-metre-wide trucks in the first instance.

What about when turning? While negotiating curves and intersections, truck and trailer combinations again require more clear area due to their total swept path, due to the tendency of the trailer(s) to ‘cut’ the corner of the path taken by the truck.

Total swept path during a 90-degree turn for a truck and semi-trailer combination (Image source: ARTSA)

The impacts on swept path due to truck (and trailer) width increases were recently investigated by the National Heavy Vehicle Regulator in their PBS Low-Speed Swept Path (LSSP) review Discussion Paper. The paper reported swept path performance for various configurations of trucks and trailers while varying truck and trailer width between 2.50 and 2.60 metres.

In all cases, the magnitude of the difference in performance between the narrowest and the widest versions of the vehicles assessed was around 1 per cent of the total result. The clear space allowances for turning manoeuvres at intersections in Australia are not tuned such that these increases in total swept width could not be safely accommodated.

The New Zealand experience regarding increased truck width offers a useful case study. Heavy vehicles have been permitted to operate at 2.55 metres wide across the ditch without any restrictions since 2017. Importantly, there has been no reported or anecdotal evidence that the wider vehicles are more likely to be involved in a crash.

Locally, there is a substantial fleet of heavy vehicles operating in Australia at 2.55 metres, either through exemptions or permits from the National Heavy Vehicle Regulator or through the Australian Design Rules and Heavy Vehicle National Law. Again, there are no published findings regarding the reduced safety or increased crash risk of these vehicles.

These factors, and others, led Austroads to conclude in their 2019 review of heavy vehicle dimensions that there is a positive case for increasing the Australian width for trucks to 2.55 metres. As the collective of the Australian and New Zealand transport agencies, representing all levels of government, Austroads is entrusted with providing high-quality, practical and impartial advice.

So, are wider trucks going to be less safe? Categorically, no!

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