Vail Daily column: Colorado’s roadside whack-a-mole
Just the Facts
Colorado potholes are becoming more abundant. Ka-thunk! Hundreds of thousands are repaired every year at an annual cost of $8 to $25 apiece. Ka-ching!
And our roads develop more potholes than most other states. Even on newish residential streets, alligator cracks quickly become potholes.
A generation or two ago, Colorado had fewer potholes per mile of road, despite the fact that street pavements weren’t as highly engineered as today. Yesteryear’s roads were less traveled, speeds were slower, vehicle weights lower and there were fewer trucks per capita using our streets.
These factors are relevant because the impact of vehicles on pavement’s pre-existing weaknesses is what triggers and then exacerbates potholes. That impact is mostly governed by how fast tires hit the pavement, how much weight is riding on a tire and how hard the tire is. For example, truck tires, inflated to 100 pounds per square inch, are tougher on pavement than are most 32 psi car tires. Tires cooled by winter temperatures are more rigid and hit pavement harder than do tires warmed by summer heat.
Today’s trucks are heavier, drive faster and travel more on local streets and highways than a half-century ago. Many are overweight. Cars are also heavier, have tougher tires and travel at higher speeds than back in the day. Put these factors together and potholes blossom.
The road type can also make a difference: interstates and major intersections are usually 10-inch thick concrete, whereas most highways and urban streets are asphalt. Both use a mix of gravel, pebbles, and/or sand, held together by cement or tar. Major arterials might have 12-inch thick beds of asphalt atop a roadbed of crushed rock or sand, whereas residential streets might only have 2-3-inch pavement.
CLIMATE PACKS A PUNCH
But the big kahuna of pothole production is our climate. That’s because our high-elevation weather is dominated by oscillations above and below the freezing point of water. Our winter and spring days are often warm and sunny. This makes our winters enviable — but frequent daily forays above freezing followed by subfreezing nights wreak havoc on roads.
Warm days allow water from rain and melted snow to drip down cracks in the pavement and enter the soil that underlies the road. Once below the pavement, cool nighttime or next-day temperatures cause the water to freeze. Frozen water expands by about 10 percent — enough for a subsurface puddle to buckle the pavement upward. Once the soil thaws out, it slumps back to its original position, but the buckled pavement doesn’t. All it takes is the right whack of a tire to dislodge a chunk of the weakened roadway.
Potholes form where these weak points experience heavy traffic. They can also form where a pre-existing weak point exists, such as where two different road types intersect, like where asphalt meets a concrete gutter or manhole cover. But the most common roadbed weakness that leads to potholes is where streets are cut by utilities.
Colorado has a team of road wranglers that keep potholes from getting out of control. Prevention is the first tool — they beat potholes to the punch by sealing cracks or embalming alligator-skin streets with oily slurries. Where roads are beyond such preventative maintenance, they strike a middle ground by scraping off the top of the road and redepositing it with new asphalt and goo. But it’s hard to keep up with the demand for road maintenance, so as the pavement ages and fails, they also play pothole whack-a-mole. In rushed or stormy situations they mash asphalt into holes as quickly as they can — a temporary fix.
Given these factors, potholes seem like they will always be with us.
My only advice: If you’re about to hit one, just roll over it. Hitting the brakes compresses your suspension before or on top of the impact event. It’s about as helpful as tightening your arm muscles just before the nurse gives you a shot. Ouch!
James Hagadorn, Ph.D., is a scientist at the Denver Museum of Nature & Science. Suggestions and comments welcome at firstname.lastname@example.org.
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