Potholes – what are they and how do we stop them?

One of the most annoying things experienced by road users (apart from sitting in traffic, of course) is potholes.

These are frustrating for cyclists and motorists not just in terms of ride comfort and safety when a pothole is severe, but also because they mean repairs need to be made. Repairs mean road works, and depending on the location of the pothole these can be tricky.

At present, the road surfaces of the bridges are in reasonably good condition but we are always monitoring any surface defects. However as we are on site, now is the perfect opportunity to carry out a full resurfacing to ensure there’s less chance of potholes developing in the future.

So how are potholes created?

The simple answer is through a combination of water, temperature changes and traffic, three things which the bridges have in abundance.

Potholes are formed by a process known as freeze-thaw action. Water seeps into tiny cracks in the road surface, and then during colder conditions it freezes. Have you noticed how water in ice cube trays is bigger once it’s frozen into ice cubes? The same thing happens to the water inside the tiny cracks, only in this case the water will have seeped into and under the surface, so it can’t easily expand upwards in the same way as an ice cube. Instead the gradually freezing water expands against the tarmac, pushing it in all directions and ensuring the crack gets a little bigger.

Then, as is common with the British weather, the temperature changes and the ice melts. As this happens the road surface loses the support of the tiny piece of ice that was forcing at the crack, so it slumps a little. This small, weakened area of road surface then gets further pummelled by the act of traffic running over it. 

The whole combination means the crack grows and weakens and small holes form in the road surface, these then get a little bigger each time larger volumes of water collect, freeze and melt – and with each passing of a vehicle’s tyre too – until they become the large, deep potholes every motorist hates.

What can be done about them?

We’ll be honest with you. There’s no guaranteed way to prevent potholes. However, knowing that they form because of imperfections in the road means we can take action to minimise the chances of them developing. One of those actions is regular maintenance, which is why we take so much effort to keep the bridges in good order.

A bigger step is to minimise the chances of imperfections in the road surface. Because potholes form in cracks, they can be common occurrences around joins in tarmac, or around utility covers or ducts. We try to minimise all of these on the Trust’s assets, and during the Rochester Bridges Refurbishment Project we’ll be taking a significant step towards preventing potholes, when we get to the end of each phase of work. Each bridge will be completely resurfaced once all the refurbishment work on that particular structure has finished.

The Bridge Engineer, Arcadis, has designed the order of the resurfacing to reduce the likelihood of potholes developing by making sure any joins in the surface will be located underneath lane markings, instead of underneath the route taken by wheels. This means there will – later in the refurbishment project – need to be a short-term closure of one bridge, and then later of the other, to enable the resurfacing to take place. The public will be given as much advance notice as possible.

Hopefully, now you understand the why and the how, you’ll forgive us that moment of larger disruption, for the good of a reduction of works and potholes in the future.

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