With freeze-thaw conditions prevalent across much of the country, American motorists may wonder why potholes often linger until spring. The reasons are a combination of physics and economics.
First, it helps to understand the consequences. In winter and early spring, drivers everywhere are plagued with blown tires, cracked wheel rims and alignment issues that happen when they drive into one of the millions of potholes that occur in both asphalt and concrete pavement. The Independent Insurance Agents of America reported in 2013 that car repairs from pothole incidences cost about $5 billion annually, with the typical repair bill about $350.
Unfortunately, most local and state departments of transportation (DOTs) can’t keep up with propagating potholes because they tend to concentrate in a three-month timeframe. Potholes form primarily during February through April, with regional variation, when temperatures fluctuate above and below freezing.
It’s also physically hard to repair potholes at the very time when they become most prevalent. When temperatures are low, it’s almost impossible to work with hot asphalt because it cools in the trip from the plants where it’s made to the roads where it is needed. In fact, in the colder (northern) parts of the U.S. the asphalt plants shut down altogether between November and March – it’s simply not economical for them to operate because so few customers can use their product in those months. Even trucks that are specially equipped with heated compartments can only reach so many potholes in the course of a workday to repair the streets.
Additionally, fixing potholes in winter is difficult due to moisture: snow, ice and water naturally collect in the holes and cracks. The existing pavement needs to be dry for most asphalt mixtures to “tack” to form a solid, permanent bond. If moisture remains in the hole it can start the deterioration process all over again: freezing, expanding and allowing room for more precipitation to enter and expand further as the temperatures drop again below 32 degrees.
The solution used in most places is to throw looser, temporary cold mix asphalt into holes to minimize potholes for a few weeks at best. When warmer and drier conditions prevail, road crews return to lay in a more permanent hot mix.
There are types of permanent cold mix asphalt that can be used in winter, and in some situations DOTs in fact use them. They tend to cost more however the combined expense of materials and labor associated with temporary pothole repairs made two, three or more times in a single season might make the permanent cold mix asphalt more cost effective in the final analysis.
Another method used by some DOTs involves pothole repair vehicles equipped with special apparatus that heats affected pavement and uses high-intensity air blowers to dry it, after which the hole can be adequately repaired. But methods of this type require the purchase or leasing of dedicated machinery. The New Jersey DOT leased six such “Pothole Killer” vehicles in 2011 at a cost of $337,000 for four months.
That’s why spring and summer are road repair months for most of the country. Before that work gets done, drivers need to be alert and drive with caution – or pay for it at a car repair shop.