The best way for HCT vehicles and cyclists to share the roads

Is it possible to combine cycling and new duo-trailer trucks on the same roads? How are cyclists affected when being overtaken by HCT vehicles 34 metres long? A study being conducted at VTI culminates in a clear recommendation for safe overtaking.

The first day of December marks one year since what are known as HCT (high capacity transport) vehicles – duo-trailer trucks up to 34.5 metres long – were given the green light for use in Sweden. These vehicles are primarily allowed to use roads divided into lanes, but they can also use a number of access roads where people may cycle. Road trains are now allowed to use a total of 5,900 kilometres of national roads.

VTI has been working in partnership with Volvo to examine how cyclists are affected when being overtaken by HCT vehicles. The experiments were carried out in a large hall, and involved looking at what happened when a standard truck and a duo-trailer truck overtook a cyclist at two different speeds (50 and 80 km/h) and three different distances (1, 1.5 and 2 metres). Air pressure, directional stability and subjective perception were all measured.

For reference, one overtaking manoeuvre also involved the standard truck switching lanes completely during the overtake.

“We already know that poorly executed overtakes are a major source of insecurity and put a lot of people off cycling. Cyclists are scared, quite simply,” says Katja Kircher, research leader at VTI.

The trials show that speed and the distance to the overtaking vehicle have the greatest impact on both the airflow and the subjective perception. The closer and faster the overtake, the more the cyclist is affected. Vehicle length is also significant, but not to the same extent.

That said, the cyclist’s position was not affected by distance, speed or vehicle length.

“That came as a bit of a surprise. However, that may be because the cyclist was resisting and really concentrating on cycling in a straight line. We could see that the cyclist’s course varied more immediately after being overtaken,” says Katja Kircher.

The study recommends that HCT vehicles should switch lanes completely and, on narrower roads, reduce their speed slightly to make overtaking as safe as possible. It is also important for the driver to make sure that the whole vehicle has passed the cyclist when completing their overtake.

Katja Kircher would also like the recommendation to be incorporated into a regulation and made formally binding. She does not think much of the current rules on “safe distances”.

“Who decides what is ‘safe’, the driver or the cyclist? No, Sweden is a long way behind a lot of other countries in that respect. Cyclists must be able to trust vehicles to overtake safely, and a regulation would also help drivers as this would eliminate any doubt as to how overtaking manoeuvres should be executed.”

One potential advantage of HCT vehicles from a cycling perspective is that using longer trucks reduces the number of vehicles on the roads, and hence the number of overtakes in general. But that said, it takes longer for such vehicles to overtake and a longer clear view of the road ahead is required, which are both disadvantages. This may increase the risk of queues forming behind the HCT vehicle.

“These and other matters need to be investigated so that we can obtain an overall view of the impact of HCT vehicles on cyclist safety,” says Katja Kircher.

Translation: CBG

Below some pictures from the project: