Letter to the BBC about truck weights…

Dear ‘More or Less’

I enjoyed your segment about the effects on EV’s roads and bridges.  I agree with your analysis, but you missed an important part of the story.

A couple of times on the segment it was mentioned that we don’t have to worry about the effects of heavier cars because roads and bridges are designed to handle lorries. That is correct.  What was not mentioned is that lorries are also going electric, with large batteries that will make them 2 or 3 tonnes heavier than conventional diesel vehicles. So, the important part of the question that you didn’t answer in the segment is: ‘Will the shift to electric lorries cause problems for road surfaces and bridges?’ 

To answer this question, it is necessary to consider road surfaces and bridges separately, because they are designed for different loading cases… Road surfaces are designed to withstand the stress caused by individual wheel forces (up to nearly 6t on the drive axle of a 40t lorry), whereas bridge structures are designed to withstand ‘traffic jam’ loading of a line of lorries.

It is also important to know that the weights of lorries and their individual axles are prescribed by regulations.  So if a heavy lorry has to carry a heavy battery, it (probably) has to carry less freight.  This will ensure that its total weight and the individual axle weights all stay within the allowable limits.

Some details:

About 60% of lorries in the UK carry low density goods- like mixed groceries or parcels.. Those vehicles can be completely filled without reaching their weight limits. In most cases, even with the addition of a heavy battery, they can carry a full load, without exceeding the weight regulations…

For the other 40% of lorries that carry high density goods – like chemicals or construction materials – it may be necessary to reduce the amount of goods carried by each lorry to account for the weight of the battery.  Again, the allowable weight limits may not be exceeded, so each vehicle will have to carry a bit less freight and additional lorries will be needed to transport the same amount of freight as now.  This means that the cost of moving these goods will have to go up to compensate for the fact that each lorry journey can carry less freight than a diesel truck. Because slightly more lorries will be needed on the road, there may be a (small) proportional increase in road wear.

It is also necessary to account for any changes to weight regulations that the Department for Transport may introduce. It currently appears likely that regulation changes associated with electric lorries will be restricted to 5-axle lorries (2 axles on the tractor and 3 on the semitrailer).  These currently have a gross weight limit of 40t and it currently seems possible that this limit will increase to 42t, but without any change to the limits for the individual axles.  This change will not affect the loads carried by the heaviest 6-axle lorries (3 axles on the tractor and 3 on the semitrailer) that can currently carry up to 44t.  So the fact that the individual axle load limits will remain the same means that road damage will not be affected, and the fact that the heaviest trucks will not get a weight increase means that bridge loads will not increase.

The overall conclusion is that the rules enforced by the Department for Transport will ensure that our roads and bridges are safe even though lorries will have to carry heavy batteries. A small increase in road wear may be observed, depending on any changes in the weights and dimensions regulations, but it won’t make very much difference.


David Cebon