How to break a bridge with the weight of too many padlocks

A couple attaches a padlock with their names on it to the Ponts des Arts, Paris. Image: Getty Images.

Above is the Ponts des Arts in Paris. In recent years it has become necessary that any two lovers visiting the city together write their names on a padlock and attach it to this bridge, and then throw the key away into the river as a gesture of eternal love.

There are now so many padlocks, in fact, that it’s resulted in structural weakening. On Sunday evening the bridge was evacuated after a section of railing collapsed under the sheer weight of love (helped along, for what it’s worth, by rust). City authorities around the world have taken to asking couples not to do the same and leave padlocks on their bridges either, both for structural and aesthetic reasons.

Something Jean-Pierre Lecocq, the mayor of the 6th arrondissement, said caught my eye:

"One can really wonder about the long-term capacity of this bridge to bear such a weight,” Jean-Pierre Lecocq, the 6th arrondissement's mayor who is opposed to the locks, said on his website Monday.


Reports have said that most of the locks on the bridge weight between 50 and 90 grams, so let’s take a neat 75g as our average. Looking at the dimensions of locks on Amazon, I'm going to say it's reasonable to take 40mm by 20mm by 10mm as a median average of the dimensions of a standard key padlock that a tourist would be able to buy in any non-specialist shop in Paris.

Currently, the bridge’s railings on both sides, for the full 150m length, are completely filled with locks. I can’t find a measurement for the height of each railing, but from pictures of people walking on the bridge they look to be a touch higher than waist height. Call it a metre. That gives us 150m divided by 20mm = 7,500 padlocks per row, and enough space for 25 rows (1m divided by 40mm) gives us 187,500 padlocks per side, or 375,000 across the whole bridge. At 75g each, that gives us roughly 28 tonnes.

(Seeing as other estimates I've seen have varied from 10 tonnes to 93 tonnes, and that pictures of the bridge show that there are so many locks on it that in some places there are layers of locks attached to other locks, this seems like a reasonable estimate that is, if anything, perhaps a touch on the conservative side.)

To put 28 tonnes in perspective, the average European human weighs 70kg. Those locks add up to equalling just shy of 400 extra people standing on the bridge at all times - or, about 12 ice cream vans, since this is a tourist attraction. For a pedestrian bridge that seems… unwise.  Unfortunately, there doesn’t appear to be any kind of record of the max weight load of the Ponts des Arts online (but if any French-speaking readers know I’m wrong on that, please correct me).

This completely demands me to wonder: How would some other famous bridges cope with the weight of Ponts des Arts-style love?

(Note: A bridge’s stated weight limit isn’t the point at which it collapses, but rather an estimate by an engineer about the point at which regular loads will probably start to cause damage. Cracks, wobbles, that sort of thing. It's not going to cause the bridge to collapse immediately, but it could, given lots of time. Moving loads are more dangerous than static ones, and while padlocks clearly don't move much, their added weight could cause some unexpected problems when combined with normal traffic.

Tower Bridge

London’s most iconic bridge has a weight limit of 18 tonnes, which is reportedly exceeded about six times a day by truckers unaware that they're too heavy. Since the support cables are so thick, the only place you can really attach padlocks to are the ugly safety barriers that runs the full length of it to keep pedestrians and road traffic apart. They look about a metre tall, with vertical rails that might hold something like a hundred of our sample padlocks each. I counted the number of rails per section using photos on Flickr - it’s 15, so 1,500 padlocks per section - and each section looks roughly a metre and a half wide.

That means we could fit something in the order of 489,000 padlocks across the whole bridge - or 36.7 tonnes, twice the weight limit.

Tourists, please do not start attaching padlocks to Tower Bridge.

Clifton Suspension Bridge

Brunel’s 1864 bridge crosses the Avon from Somerset to Clifton, a suburb of Bristol, and was one of the world's first suspension bridges. Its 81 vertical iron rods are thin enough for padlocks. The longest is 20m, the shortest 0.91m, so let’s say it’s the same as if each was around the mean length: 10.45m.

That should be 1,045 per rod, or 84,645 across the whole bridge, giving us roughly six and a half tonnes of padlocks. Since the bridge’s weight limit is four tonnes, introduced more than 50 years ago over fears that the listed structure might collapse under the weight of modern vehicles, this is not good. I was going to include the extra strain from padlocks attached to the railings on the sides but that would likely be overkill.

As an illustration of the differences between static and moving loads, when the bridge was first opened engineers had 500 tons of stone rubble laid out evenly over its surface to test its load-bearing capacity - it reportedly sagged by as much as seven inches without breaking. Yet large crowds of people, who collectively only weigh a few tonnes, are often stopped from going on the bridge because the way people walk, and the way that they clump together into unevenly-distributed clumps, can cause swaying that genuinely does threaten the bridge's structural integrity.

Tourists, please do not start attaching padlocks to the Clifton Suspension Bridge.

Golden Gate Bridge

As with Tower Bridge, the upright cables are too thick for padlocks. There are, however, some useful railings running the length of the bridge to separate pedestrians and traffic. The railings can take seven rows of padlocks (judging from pictures like this), so for the 2.7km of bridge that makes something like 3.78m million padlocks with a combined weight of around 283 tonnes.

The bridge’s capacity is apparently “4,000lbs per lineal foot” - or roughly six tonnes per metre - which, thankfully, is far above the ~100kg per lineal metre of padlocks we’d see attached to the railings. To reach that six tonne/metre limit, tourists would have to attach padlocks onto other padlocks and onto other padlocks and on and on, until there was a mass of padlocks 60-deep, partially blocking the pedestrian footpath and likely causing traffic congestion.

Tourists, feel free to attach padlocks to the Golden Gate Bridge.

Images: Getty.


Why is it acceptable to kill someone? On the mysterious history of Britain’s road death toll

A London speed camera, 2004. Image: Getty.

A decade ago I became fascinated by a graph. This one:

I had been tracking the underlining data for years. The figures were easy to remember. Every year it was 3,500, plus or minus a percentage point or two.

Yet when the 2008 data was released, it had fallen to 2,538. This was 1,000 less than the figure in 2003. I plotted the above graph, and as I said, I became fascinated.

Because this is a really important graph. This is a plot of the number of people killed on Britain’s roads each year.

In Great Britain, collectively, we used to kill nearly 3,500 people on our roads every year. Consistently or, dare I say it, boringly: 3,500 deaths a year, 10 a day. It was accepted, in a, “Well yes it’s bad, but what can you do about it” kind of way. There was no clamour for change. Newspapers weren’t running headlines about the deaths mounting up, as they do with knife crime.

Meanwhile a train crash would be front page news for a week. Take the train that derailed at Hatfield on 17 October 2000, a tragedy in which 4 people died. That led to huge media interest, massive upheaval on the railways, and, ultimately, as the re-nationalisation of Railtrack, whose failings had caused the crash. Yet more than twice as many people will have died on the roads that day. Nothing was written about those deaths. Nothing changed.

In 2000, four people died in train crashes, while 3,409 died on the roads.

Here are those figures again.

1997 – 3,599 people killed on our roads

1998 – 3,422

1999 – 3,423

2000 – 3,409

2001 – 3,450

2002 – 3,431

2003 – 3508

But, in 2004 the figure dropped below 3,400 for the first time, to 3,221. Then in 2005 to 3,201.

2006 – 3,172

2007 – 2,946

Below 3,000! This was change. Significant change: 500 lives a year were not being lost. If you use Britain’s roads, your life may have been one of them.

2008 – 2,538

2009 – 2,222

When the 2010 figures came out I was amazed by the headline figure: 1,857.

That’s still far too high, of course, but it was 1,701 lower than seven years earlier.

This was a major story that deserved a ton of coverage, which it failed to get. Having shown no concern for when we were killing 3,500 people, it wasn’t overly surprising that the fact we were now killing 1,700 fewer wasn’t celebrated.

At any rate, the graph had flat-lined for years, then, in half a dozen years, it halved. Why?

The lack of media coverage resulted in an absence of answers. One commentator, Christian Woolmar, observed that there was no clear answer to why this had happened. But he went on to point out that there had been a fall in the average road speed over this period.

My anticipation of the 2011 figures troubled me, because I expected them to go up. Obviously I didn’t want them to: I desperately want zero deaths on our roads. But something happened in 2010 that I was sure would lead to more fatalities and bring a halt to the falling trend.

I was right. In 2011 we killed 1,901.

Sometimes, being right is shit.

The news was better in 2012. The fatality rate was 1,754. So was the 2011 figure just a blip, due to some significant snowfalls that year? No: the trend was over.

The number of people killed on our roads has remained stuck in the 17 hundreds. 

2013 – 1,713

2014 – 1,775

2015 – 1,732

2016 – 1,792

2017 – 1,793

2018 – 1,782

We have returned to a flatline on the graph – and if anything, I’m more fascinated now than I was before. Road deaths flatlined at 3,500 for years, then fell sharply, then flatlined again at half the rate.

This can’t have happened by accident. I wished I could explain it. I wish we could repeat it. No: I wish the second flatline hadn’t happened, and the fall had continued. If the rate of fall had continued, we’d have reached zero deaths on the road by now. You’d be right to question whether this is possible – but if you can half the number in a few years, why can’t we eradicate them altogether? The railways are an example of what is possible. The last time a passenger died in a train crash on Britain’s railways was in 2007.

It was time to figure out the answers to two questions. Why did the death toll fall? And why did it stop falling?

The obvious reason for a reduction in deaths on the road is the improvement in car safety features. This could create a gradual fall in the death toll as new, safer cars replaced older ones. But I’m not sure it can explain a 40 per cent fall over a 4 year period.

There’s a way to check whether cars on the road became almost twice as safe between 2003 and 2010: you can compare the figures with the rest of the EU. Car safety features are international, and any new feature would have appeared around the same time across the continent.

So I found the EU figures for 2000 to 2017, indexed for 2000 and plotted the graph for multiple countries. It was a busy graph. For clarity the following graph only includes Britain, Germany, France, Spain and Italy along with a straight line drop for comparison.

The good news is that things are improving across Europe – but no country had quite the same trajectory as Britain. They all have a fall much closer to a straight line of the sort you’d expect a general improvement in car safety would produce.

One thing I did notice is that, from 2013, these five countries stop falling. The technology based solutions of recent years, such as automatic emergency braking, don’t appear to be saving lives as of yet.

So, yes, cars are safer – but that doesn’t seem to explain why British roads suddenly became 40 per cent safer between 2006 and 2010.

In 1999, the New Labour government announced that it was going to reduce deaths on our roads. The target was a 50 per cent reduction by 2010. As you now know, it succeeded. This was a major achievement for a government. The kind of thing you would bang on about all the time. “Deaths on our roads halved by Labour!” But the party wasn’t in government when the 2010 figures were released – and it’s hard to take credit for your achievements from the opposition benches.

That it was government policy is not a full explanation, and how this happened is a little opaque. From what I can gather there was a wide ranging approach. The fire and rescue service changed their practices: because they recognised that survival rates were directly dependent on how quickly people got to hospital, this became the priority. Disturbing a police crime scene was allowed if it saved a life. Accident black spots were located, highlighted and safety measures implemented. Throughout that period road safety campaigns focused on speed, with “Speed Kills” being the dominate message for that decade. The government also changed the laws on speed cameras.

RoSPA, the Royal Society for the Prevention of Accidents, has a lot to say about speeding and speed cameras. Its “Speed Camera Factsheet” states that, “Cameras are a very effective way of persuading drivers not to speed, and thereby reducing the number of people killed and seriously injured.” It reports that an independent review published by the Department for Transport (DfT) in 2005 said that “cameras significantly reduce speeding and collisions, and cut deaths and serious injuries at camera sites”, adding that cameras sites were delivering 100 fewer deaths per year.

Cameras first appeared in 1991, and revenue from court fines and fixed penalties went to the Exchequer. However in 2000 a trial scheme saw local councils keep the fines to pay for the cost of speed and red-light cameras. The pilot was so successful that, in 2001, legislation enabled this to happen across the country. The cost of providing and operating cameras moved from the local authority to the law breaking motorist.

The golden age of the speed camera had begun.

There was a tweak to this legislation in 2007. Fines reverted back to the Exchequer’s piggy bank. The DfT switched to funding cameras through a road safety grant. The intention was to create a greater mix of road safety measures agreed between local authorities and the police.

The number of people killed on British roads in 2007: 2,946

The number of people killed on British roads in 2010: 1,857

So perhaps the creation of the Road Safety Grant had a significant impact.

The second question: why did the death toll stop falling?

In 2010 I was unaware of Labour’s target to halve deaths on the roads. But, the change in government was enough for me to predict that the fall was over.

When the Tory/Lib Dem government negotiated its way into power in May 2010, the press declared that it was the end of the horrible nanny state – a return to personal freedom, liberty and the rule of common sense.

The way that this was to play out in real practical terms was on our roads. The evil speed camera was in the firing line. The narrative was that these cameras were just there so councils could extract cash from the poor public. Completely ignored were the facts that the fines were only handed down to dangerous, law-breaking drivers, and that councils no longer got the cash from fines.

Soon after the election the coalition government said that “Labour's 13-year war on the motorist is over” and pledged to scrap public funding for speed cameras. The Road Safety Grant to local authorities was cut from £95m to £57m. This meant that the government was now receiving an estimated £40m more raised in fines than it was spending on road safety. The cut to the grant reduced the camera maintenance budget by 27 per cent. It removed all the funding for new cameras, speed humps and other safety measures.

And the golden age ended.

Councils across the country announced their change of policy. Oxfordshire County Council switched off its speed cameras on 1 August 2010. Money was saved; lives were lost.

Eight months later, on 1 April, Oxfordshire’s cameras snapped back into life when the council reversed its decision because deaths on the county’s roads had immediately increased.

Turning off speed cameras sent out the message that we were no longer taking speeding seriously. The road safety campaigns changed their focus. The message that Speed Kills fell away and was replaced by drink- and drug-driving messages. It’s easy to miss that these campaigns move from encompassing virtually every driver to targeting a minority. A switch from confronting a socially acceptable behaviour to re-enforcing something already unacceptable. The state is no longer challenging everyone to be safe – only the small minority of bad people.

Yet speed still kills. The World Health Organisation states that an increase in average speed of 1 km[h typically results in a 3 per cent higher risk of a crash involving injury, with a 4–5 per cent increase for crashes that result in fatalities.
The majority of safety measures installed before 2010 remain in place and are saving lives. But with the funding gone councils are no longer installing new measures and the death toll is no longer falling.

So you can make a strong case that the pattern of road deaths was the result of government policy.

Which begs the question of our government: why has it accepted that it’s OK to kill, or be killed, on our roads?