How big can my deliveries be?

On a recent project I found myself needing to know what the maximum dimensions of a road delivery could be. This is critical for steel construction, where pre-fabricating saves time and money, as well as reducing on-site health and safety and quality issues.

My problem was that when designing huge steel trusses, fabricating off-site an entire truss off-site and bringing it to site on the back of a truck seemed to be the most sensible - except the trusses in question were up to 90m long. So, if I cut them into small splices and bolted them together on site, how long should my trusses be to be most economical?

According to Roymech.co.uk and RoadTransport.com, the maximum permissible dimensions depend on the type of vehicle used. This applies across the entirety of the EU.

Vehicle type	Image	Maximum width (m)	Maximum length (m)
Rigid		3.0	12.0
Articulated		3.0	16.5
Drawbar		3.0	18.75

Note that there is no limit to height, save that the load must be able to pass safely under bridges. RoyMech points out that only bridges under 4.95m in clearance are marked on maps.

Maximum weight is a difficult issue as legislation is apparently complicated. The limit depends chiefly on the number of axles. In the United Kingdom:

Number of axles	Maximum weight (kg)
2	18,000
3	26,000
4	32,000
5	40,000
6	44,000

Across the EU, the limit is 40,000kg; the additional 4,000kg applies only to transportation in the United Kingdom.

Anything greater than these dimensions or masses requires notification to the road authorities in question.

In answer to my original question, since the fabricator in question had only articulated lorries available, I was able only to use a maximum length of 16.5m. Therefore, the maximum chord length L_max of my spliced banana trusses was:

L_max = √(16.5²+ 3.0²) = 16.7m

Over a banana truss about 90m in length, this meant that splicing my truss into 6 pieces (about 15.0m of splice length) would be adequate.

Since preliminarily I'd sized my banana truss chords as Corus Celsius® 355 CHS 406.4x16.0, about 154kg/m, both truss chords would have a mass of about 28,000kg. This gives a nice 3,000kg margin of safety for truss braces if I were to ask for a 5-axle articulated lorry. Of course, I could split the truss into a couple of deliveries.