Chip Seal: A Sign of Summer

No matter what you call it, “chip seal”, “oil and stone”, “tar and feather” or “aargh, not my favorite road”, it affects all cyclists. When faced with a freshly chip sealed road, I try to be as pragmatic as possible. The more I know about chip seal, the more I’ll appreciate it.  Maybe.  I’m sharing this so your ride on chip seal will be better, too!



Chip sealing is an inexpensive, quick way to maintain a road surface. How often have you thought to yourself, “Wow, I can’t believe they destroyed this entire road in just an hour….”

Chip seals do not improve ride quality. No kidding — it’s not just the bumping along, it’s all those loose chips on the road. And the crazy drivers who bomb down the road, oblivious to all the flying chips they’re creating (technically known as “whip-off”). These losses are usually 5% on the low volume roads we ride.

But those drivers are a critical player in making all the little chips embed themselves in the sticky binder.  Unfortunately, our bicycles just can’t do it. The goal is to embed 80% of the road volume, leaving a 20% void space.

So what determines how many chips should be put down? Surely, like me, you’ve noticed that some road crews are absolutely miserly about the amount of chips they use.  But other crews must have an incredible budget based on the drifts of chips they spread. Luckily, for those who are inclined to use it, there is a formula to optimize the “aggregate application rate”:


C= (1 – 0.4V) × H × G × E


C = Cover Aggregate (kg/m2)

V = Voids in Loose Aggregate (%)

H = Average Least Dimension (mm)

G = Bulk Specific Gravity

E = Wastage Factor (%)


Brooming can generally be done within 2 to 4 hours after sealing. Hot applied chip seals can be swept within 30 minutes while conventional chip seals can be swept in 2 to 4 hours. And here’s the big question: why does it take so long to sweep the road??? What is this, seal on Friday, sweep next week routine?  There are obviously no cyclists in these crews. I’ve often thought that our local highway department thinks it’s the job of the snow plow to sweep the chips. Given the safety issues for cyclists, motorcyclists and even cars, one would think the sealing would be done in the morning and the sweeping in the afternoon.  Grumble.


My thanks to the California Department of Transportation for educating me:






  1. Kim Corcoran says

    WOW — I never knew there was any science to the inconvenience! I’ll still hate it, though! :-)

    Thanks, Georgena!

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