Traffic engineer warns of dangers of longer lorries to London cyclists and walkers

Former traffic engineer and committee member of Cambridge Cycling Campaign, Jim Chisholm, has written to his local MP to warn of the dangers of longer lorries.

Worryingly, the letter raises very serious questions about the safety of introducing longer lorries in urban areas.

As part of our No More Lethal Lorries we'll be opposing the Government's proposal in partnership with other cycling groups, as well as representatives of pedestrians and others promoting more people-friendly public spaces.

Letter concerning new Government proposals for longer lorries

Sent from:
Jim Chisholm

Sent to: Andrew Lansley, Conservative MP for South Cambridgeshire

Copied to: Julian Huppert, MP for Cambridge and Liberal Democrat spokesperson for Transport; Cambridge Cycling Campaign; London Cycling Campaign; Campaign for Better Transport; CTC

Although the formal time for consultations has just ended, I am writing as one of your constituents, to ask that the Department for Transport should not be allowed to change the regulations to permit 15-metre and longer articulated trailers without proper Parliamentary scrutiny.

I've been informed that it is possible for the DfT to introduce such changes just by an amendment to the appropriate Statutory Instrument. I should explain that as well as being a volunteer promoting cycling in and around Cambridge, I also, some 30 years ago, wrote the first effective 'vehicle manoeuvring' computer model. This could predict the space occupied by large articulated vehicles when doing complex manoeuvres at urban junctions or in loading areas.

This was developed while I was in government employ, and was later improved by Savoy Computing Services, and is now widely used by engineers and architects, not only in the UK, but throughout the world.

I was asked, by cycling interest groups, if I would attend, along with others, a DfT briefing on the issue of proposed longer lorries some few weeks ago. Having read the consultation papers and attended the briefing, I realised that the issues of the use of such longer trailers in urban areas had not been adequately explored or perhaps even understood.

Currently most, but not all, commercial vehicles are required to pass 'turning circle' tests as part of EU & C&U regulations. Similar such regulations existed only in Italy and Germany when I did my work on such issues in the late 1970s.

These tests are simplistic, and although they may be representative of turning at junctions on major trunk roads, they do not represent the sorts of turns required on a typical urban road network where such longer trailers would also have rights to operate.

Basically, in such regulatory tests the tractor unit NEVER turns as sharply as it can in practice, or is required to do in many urban situations. This already causes problems with existing length trailers because it is these sharp turns that create excessive 'trailer swing', when the rear corner of the trailer swings in the opposite direction to the turn, as well as 'cut-in', when the trailer wheels mount pavements.

Paradoxically, because the regulations are framed mainly to reduce 'cut-in', which current trailers only just meet, all the 'extra' 2 metre length will be behind the effective position of the rear axles. Rearmost trailer axles will need to be, at the least, self steering, so as to better distribute any load, but this cannot reduce the 'effective' rear overhang of some SIX metres which will exist on such proposed trailers.

Think of it as turning a corner carrying a long plank over your shoulder.

When executing a typical right turn at an urban traffic traffic light controlled junction the rear outside of such trailer may swing out over 2 metres. This is clearly sufficient to either damage a vehicle in an adjacent lane or any street furniture on traffic islands. The extra length makes far more than a linear increase in out-swing over existing approved vehicles.

I was also very surprised, while talking to a senior local authority engineer, to discover that it appeared that local authorities were apparently not formally informed of the consultation about proposals for permitting such longer trailers. Damage to both the street furniture and footways, by these longer trailers could be a significant, and often unrecoverable cost for local authorities.

I attach a press release on this issue that I prepared a couple of weeks ago on behalf of Cambridge Cycling Campaign. Reference is made to the death of a pedestrian on the footway, caused by the 'trailer-swing' of an articulated vehicle making a right turn at a junction within Cambridge.

I also attach a diagram produced by a local consulting engineer. This uses the Savoy Computing program Auto-TRACK to model the path of both an existing maximum length, and the proposed longer trailer through a 'template' junction typical of that found on 'A' roads in urban areas. This diagram has also been made available to national groups such as Campaign for Better Transport and CTC.

It can easily be seen, that at this typical junction, even with an ideal and tested path, virtually all turns result in either the vehicle mounting the footway or the trailer swinging a very significant amount into an adjacent traffic lane.

I ask that due technical resources are used to investigate all issue of the use of such 15-metre-plus trailers in urban areas to ensure the future safety of all road users. Please ensure that due processes in Parliament are used to investigate such issues.

Yours sincerely

Jim Chisholm

ps My work was reported on in TRL reprt SR662 "Goods vehicle manoeuvres: a computer program and its application to roundabout design" (1981) AW Christie & J Chisholm