The government has approved the use of longer lorries on British roads to make businesses more efficient, reduce emissions, and reduce traffic on our roads. But what impact will a larger vehicle have on junction layouts? What safety implications are there for other road users? And how might it affect assets adjacent to the highway? We have reviewed the implications of the longer lorries on our roads and share our findings below.

The current maximum length of a standard articulated Heavy Goods Vehicle (HGV) used in designs on British roads is 16.5m. The government has approved the use of a longer vehicle for general circulation, referred to as a Longer Semi-Trailer (LST), increasing the length of the largest vehicles on our roads by 2.05m to 18.55m. The axle configuration on the LST trailer units will not differ significantly from the existing HGV trailer, but the overhang distance is set to increase.

PJA have carried out a comparison exercise of vehicle movements around typical development access junctions to understand how this increase in length might impact future infrastructure.

The additional 2.05m length of an LST trailer unit makes little difference to the vehicle’s swept path when manoeuvring through junctions and roads, however there is an additional circa 0.5m ‘bulge’ from the rear of the trailer when turning 90° ‘full lock’ into a junction.

The increased ‘bulge’ could be a serious problem if minimum road widths are present. This is more likely to be evident in urban towns where lane widths are reduced due to available carriageway space.

The additional turning rear ‘bulge’ could also have serious safety implications to other motorists, cyclists, and road users if they are aligned in close proximity to an LST trailer.

So what does this mean for engineers and designers creating future roads, junctions and service yards?

There have been a series of well documented trials carried out by the Department for Transport (DfT) that have informed the process of the introduction of LSTs. LSTs are approved for general circulation under ‘Light Regulations’ that set out to “remove the cap on the number of LSTs, allowing the market to decide the quantity which would be in operation. Add some additional regulations which are designed to ensure the retention of positive outcomes for the public safety and effective use in comparison to the operation of 13.6m trailers”.

It’s thought that the introduction of LSTs will reduce accident rates due to removing some HGVs from traffic, however it is recognised that “longer vehicles with increased tail-swing are likely to increase the risk of accidents if operational measures to limit risk exposure are not taken” (Longer Semi-trailer Trial (publishing.service.gov.uk)).

Designers therefore should be conscious of the allowable clearances between lanes and to kerb channel lines because there is a risk of conflicts with adjacent users and the potential to cause damage to street furniture.

In urban towns, where lane widths are reduced due to available carriageway space, signage may be worth consideration to detail restrictions to long vehicles and advise drivers of LSTs to seek an alternative route. An assessment of existing road widths should be considered to see if they are suitable to accommodate the increased ‘bulge’ from an LST. Minimum lane widths for vehicles may need further consideration in Design Manual for Roads and Bridges (DMRB) and formal safety margins between adjacent lanes and channel lines is likely to need to be reviewed with consideration of the longer LST trailer safety impacts of the vehicle movements. Additionally, where existing road widths are unsuitable for longer vehicle movements, design guidance provided in Traffic Signs Manual may need to be updated to provide guidance of signing restrictions to long LST trailer vehicles. PJA have highlighted that there may be a requirement for updates/clarifications requirements within the nationally recognised design standards currently applied to the design of UK roads.

We are also currently reviewing the impacts of longer LST trailer units on ‘Designing for Deliveries’ design guidance. The longer trailers are likely to impact parking layouts and may have a significant impact on the dimensions and allowances currently applied. We will endeavour to keep you informed following our further investigation into the anticipated impacts.

If you are concerned about your service yards already being limited in terms of vehicle movements, we can undertake a quick check of your service areas based upon the larger vehicle dimensions and advise on possible implications.

Typical developments of concern may be those which have recently received planning permission or due to be submitted.

Please don’t hesitate to contact us for assistance.

 

Conclusions

There’s no doubt that a decrease in HGVs on our roads is a positive thing. The introduction of LSTs should reduce traffic, improve air quality, decrease emissions, and make deliveries more efficient and cost effective whilst realising carbon savings and highway wear and tear. However, only time will tell if the balance of removing vehicles is equalled by the introduction of fewer longer vehicles with a heightened risk of potential accidents. Driver training will be integral to making this a success.

Design standards may need to be updated and wider roads/larger parking areas are likely to be required to accommodate the longer LST trailers. The requirement for increased carriageway widths could potentially impact land available for development projects. An assessment of projects to ensure the most viable and sound solution is achieved should be taken to retain the highest value for development.

 

Please do not hesitate to contact us if you need advice regarding concerns regarding associated developments/improvements which may need to accommodate longer vehicles.

For more guidance or information please contact:

Andrew Nixon
E: [email protected]
T: 0121 387 7918
M: 07976 484076

 

N.B. The vehicle profile used in our analysis is PJA’s interpretation of the LST trailer and no approved trailer profile has currently been released to officially represent an LST trailer.