HCT: Do longer trucks affect road safety?

Trucks seen from behind.
Photo: Semi Trucks Traffic

Trials of longer, heavier vehicles have shown that they can help reduce climate impact by increasing transport efficiency. Fewer trucks carrying more cargo in a single consignment use less fuel per tonne of goods transported, which in turn results in lower emissions. Several ongoing projects examine how they affect transport safety.

It all began with the forest industry in Finland, where there was a desire to load more timber on each truck and trailer combination, and the forest industry in Sweden was quick to follow suit. The benefit in those days was provided by being able to transport heavier loads, and the maximum gross vehicle weight is now 74 tonnes on roads that are capable of accommodating that weight: these are known as BK4 roads. The possibility of using longer trucks has been investigated since then, and on 31 August the Swedish Road Traffic Ordinance was amended to allow road trains up to 34.5 metres long.

This is known as high capacity transport, HCT. This may be a more logical concept than the Swedish “longer, heavier vehicles”, because vehicles do not always have a higher gross weight as well as being longer. Jesper Sandin is a senior researcher at VTI and is currently involved in a number of research projects focusing on longer vehicles.

“In the case of volume goods that aren’t all that heavy, we need longer trucks, not heavier ones, if we’re to achieve capacity gains,” says Jesper Sandin.

But could road safety be put at risk if longer trucks use our roads?

“Longer trucks will operate on motorways initially, and we don’t expect to see an increase in the risk of accidents as they’ll have at least two lanes in either direction and be separated by a central barrier. In Australia, HCT vehicles have been operating on motorways for at least 30 years and , and which have a lower risk of accidents compared to conventional trucks. However, Sweden has a lot of rural roads without central barriers, and we need to examine if there might be adverse effects there. That’s why we’re now studying how longer trucks might affect road safety for cyclists who are being overtaken, and for cars overtaking the longer vehicles.”

For cyclists, tests have been conducted on an indoor test track where 22 experienced road cyclists were asked to cycle on rollers on a fixed platform. They were then overtaken by two trucks of different lengths, 16.5 and 32 metres. Both trucks passed the cyclist at different speeds, and with varying lateral distances to the cyclist.

“The initial results show that cyclists mainly feel that the truck’s speed and the lateral distance to the truck are what affect their sense of risk and discomfort when being overtaken, not the truck’s length. We’ll be comparing these results with a study on a real rural road in 2024.”

Results from 2011 are available regarding the safety of cars overtaking long trucks. VTI studied passenger cars’ overtaking manoeuvres of trucks 30 metres long, both in a simulator and in real traffic on the roads. The studied indicated no clear increase in risk at overtaking manouvers of accidents. The researchers will now go further and work together with the Swedish Transport Administration to calculate the overtaking distance, the overtaking time and the necessary visibility distance for 34.5-metre vehicles, taking into account road layout and visibility class.

On 1 December, the Swedish Transport Administration presented which roads with central barriers in the state road network can be used by longer vehicles. However, it will be some time before they are seen on the roads to any great extent. That said, it is important to involve as many stakeholders as possible in planning and evaluation: road users, the automotive industry, researchers and, not least, municipalities, as well as the Swedish Transport Administration. To get to and from their final destinations, such as freight terminals, longer vehicles often need to drive on road stretches that are maintained by local authorities and where vulnerable road users may be present. That is why a research study this year will examine how drivers of longer trucks interact with cyclists when turning off roads and crossing footpaths and cycle paths.

There is a growing interest in HCT throughout the rest of Europe, and Jesper Sandin presented results from previous projects at an international conference in the autumn. Sweden and Finland have made the most progress in Europe when it comes to raising their maximum gross weight and length limits, and Finland has been quicker to introduce new rules. Things have gone well there from a road safety and accessibility standpoint, and of course this provides guidance for Sweden.

The research projects are being conducted in cooperation with partners such as Volvo Trucks and the Swedish Transport Administration, and are being funded by VINNOVA (FFI, Strategic Vehicle Research and Innovation), the Swedish Transport Administration and the Swedish Energy Agency.

Text: Hillevi Ternström

Translation: CBG

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