Road bridge weight limits.

The other day on my way to the museum, I was overtaken by 4 fire engines in full panic mode. They must have passed over the railway on bridges which were restricted in weight capacity. Do they have special dispensation to overload bridges?

Bridge and other civil engineering weight limits are generally very conservative. If the engineers have done the sums right and there are no issues with the underlying geology they are set for safe continuous use over many years even if the structure has sustained moderate, not yet noticed or repaired, damage. Theoretically considerably more than the usual engineering X3 fudge factor.

A few moderately excessive vehicles nipping over on occasion will be irrelevant. Especially if its one vehicle at a time.

Clive

Nowadays you can bet several risk assessments have been made, two committees have discussed it several times and commissioned an in depth report from someone's brother-in-law and the drivers have been on a special 'Safe Bridge Crossing' course.

A quick google (I must have nothing to do!!   Shows the only available limits seem to be 7.5 t or 3 t. Therefore a bridge that would be safe for, say, a load of 20 t and would therefore no be strong enough for a 44ton lorry would still have to be restricted to 7.5 t.

Crazy system.

And i may well be wrong anyway.

It all depends on the local TRO in force. It may, or may not exempt emergancy service vehicles (or it may only exempt them whilst responding to an actual emergency). Usually, unless the structures are in distress they are exempted.

This was an issue for Chertsey bridge IIRC where they imposed an18tonne weight restriction due to the bridge requiring strengthening work, but after the work was completed they kept the exemption in place to protect the bridge from damaging traffic but it didn't allow an exemption for emergency services.

In South Africa when applied for permits to take abnormal loads on the roads. The rules when crossing a bridge was not accelerate, decelerate or brake as this lessened any damage to the structure.

If we were half way across and some idiot pulled onto the bridge you didn't stop you just pushed them back they way they came!

Yes.

Maybe they toss coins for who goes over first.

Yes, if one fell onto the railway line it would certainly make the headlines.

Most bridges will have a Military designation for what load it will carry. I have looked but at the moment cannot find details. tanks and heavy vehs would be routed to miss bridges that did meet the weight spec for 60 ton tank

Newbridge (second oldest crossing over the Thames) had its rating reduced to 18 tonnes MGW after numberous HGVs were damaging the structure. The engineers calculated that one of the arches shouldn't support its own weight. The 13thC Bridge designers obviously knew better.

Real road ballsup in Brighton. Council contractors remaking Western Rd into a fancy kerbless area and buses westbound only. 600+ eastbound bus journeys per day, diverted up Montpelier and into Upper North st then down Regent Hill and continue east along western Rd. The council suspended the 7.5t weight limit in Upper North st to allow this diversion. 600+ buses a day at around 11t+ empty but could have 70 passengers average 12stone (1.5cwt) = another 5+ tons! Result 2 busted water mains and one gad main. So, close road fro Repairs and buses continue North to 7 dials roundabout and work their way around more narrow back streets to top of Regent Hill. I believe this crazy arrangement will still be in operation til sometime next year. In the meantime the road workers appear to be acting like it's a casual hobby. Over 16 tons on a previously 7.5t limit road?

I have seen double decker busses going over these bridges, I had no idea how heavy they were.

a picture paints a thousand words

https://goo.gl/maps/DhJpiwZYXT5JXq257

but this is such  small bridge, an artic running at 44t could not get all its axles on the bridge in one go.

Edited By Justin Thyme on 24/04/2023 16:29:50