Potholes, cars, and water

March 5, 2023

One of those “you cannot unsee it” things, for me at least, has been the way that partly damaged roads become badly damaged roads whenever it rains and cars continue to drive on them, especially at speed.  The cracks and potholes fill with water, and if cars and trucks go through them rapidly, the tire jets water out of the pothole, and that water jet helps erode the pothole, quickly.

The discussion I find about this searching the internet seems to talk less about cars and this splashy dynamic wear, and more about how water in a pothole seeps into the road bed, weakening it and leading to subsequent accelerated road wear.  Finite elements modeling of pothole water jets seems like a fun project for someone who knows how to do that sort of thing, it would be nice to know how that wear depends on car speed (if it depends on car speed).

Concord Ave in Belmont uphill from Cambridge line, showing several potholes filled with water and old patched potholes, together with debris sprayed out of the potholes including small rocks.

The spraying action is much more obvious on the separate, raised cycle track a little further down the road, where the debris spray patterns are more preserved:

PXL 20230302 143019089

I’m not sure what’s the best way to handle this.  I ride a bike most days, even the rainy ones, so I’m usually not making the problem worse.  More aggressive crack sealing (look further out in the lane in that photo, there is a long crack in the road that will not get better) and pothole maintenance would probably help, but those things cost money, and “someone” votes against gas tax increases (and the gas tax is currently too low, road repairs are subsidized from other funds).  Another possibility, when the potholes are concentrated in one lane, would be to block off the lane on wet days.  Long term, for patterns like this, it might make sense to use a thicker layer of tarmac or a firmer roadbed to reduce wear (in the adjacent-to-cycletrack case, the water table is not far below the road, and there’s also a reasonable amount of heavier truck and bus traffic).

This stretch of Concord Avenue has been susceptible to potholes as long as I can remember.  Before it was repaved to add the cycle track, I remember treating it as a no-go zone for bikes, because it was both multilane AND throughly potholed along the edge, meaning a substantial risk of swerving into traffic either to avoid a pothole or because of hitting a pothole.

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