question: Why are there always extremely pronounced potholes in an otherwise normal stretches of roads just days after snow and salting?
comment: Freeze/thaw cycles crack the pavement, and then a plow comes along, catches the crack, and rips out a chunk.
passages: Water trapped under the pavement softens the subbase and subgrade, making the road more vulnerable to traffic loads. Water under the road freezes and expands in cold weather, causing and enlarging cracks. In spring thaw, the ground thaws from the top down, so water is trapped between the pavement above and the still-frozen soil underneath. This layer of saturated soil provides little support for the road above, leading to the formation of potholes. This is more of a problem for silty or clay soils than sandy or gravelly soils. Some jurisdictions pass frost laws to reduce the allowable weight of trucks during the spring thaw season and protect their roads.
   In areas subject to freezing and thawing, frost heaving can damage a pavement and create openings for water to enter. In the Spring, thaw of pavements accelerates this process when the thawing of upper portions of the soil structure in a pavement cannot drain past still-frozen lower layers, thus saturating the supporting soil and weakening it.
   Many other instances have been reported of heavy construction equipment vanishing into muskeg in the spring as the frozen muskeg beneath the vehicle thawed. Construction in muskeg-laden areas sometimes requires the complete removal of the soil and filling with gravel. If the muskeg is not completely cleared to bedrock, its high water content will cause buckling and distortion from winter freezing, much like permafrost.
   Both new and old roads often have insufficient drainage gradient at the entrance and exit of sharp outercurves, causing water pooling in rain and forming local surprising ice spots in cold climate. 
  
  A large study in Sweden (see the linked "Analysis of single vehicle accidents with fatal outcome" below) showed that fatal single crashes are 5 times more common in outercurves, than in innercurves. This extreme overrisk is considered strongly related to improper banking and insufficient drainage gradient at outercurves.
   Poor drainage in the road bed is a frequent cause of this degradation of the base or subgrade. A heavy spring thaw, similarly to poor drainage, can weaken the base course, leading to fatigue cracking. 
   The road is one of the most difficult roads in North America to snowplow in the spring. Up to of snow can lie on top of Logan Pass, and more just east of the pass where the deepest snowfield has long been referred to as the Big Drift. The road takes about ten weeks to plow, even with equipment that can move 4,000 tons of snow in an hour. The snowplow crew can clear as little as of the road per day. On the east side of the Continental Divide, there are few guardrails due to heavy snows and the resultant late winter avalanches that have repeatedly destroyed every protective barrier ever constructed. The road is generally open from early June to mid October, with its late opening on July 13, 2011, marking the record for the latest opening since the inaugural date of July 15, 1933.
   Other failure modes include aging and surface abrasion. As years go by, the binder in a bituminous wearing course gets stiffer and less flexible. When it gets "old" enough, the surface will start losing aggregates, and macrotexture depth increases dramatically. If no maintenance action is done quickly on the wearing course, potholes will form. The freeze-thaw cycle in cold climates will dramatically accelerate pavement deterioration, once water can penetrate the surface.
   The rapidly changing conditions require special cautions, relayed to motorists via variable message displays along I-90. Depending on traction they may call for tire chains to be installed, usually on large trucks but occasionally on smaller vehicles as well. Chain-up areas are provided along the side of the Interstate to facilitate the placement of chains. The pass has been subjected to closures when weather conditions become extreme.
   The entire Going-to-the-Sun Road takes about ten weeks to plow, even with equipment that can move 4,000 short tons of snow an hour. By the first of June of each year, the Logan Pass visitor center can usually be reached by vehicle from at least one side of the Continental Divide. In 2011, due to abnormally heavy late winter and early spring snowfall, the Going-to-the-Sun Road did not open until July 13th, the latest opening ever due to snow.
   As spring approaches, the region is surveyed by helicopter in preparation for snow removal that will be needed in order to reopen the Going-to-the-Sun Road for the summer season. By early April, snow removal crews working from either end of the roadway have begun to ascend the steeper east and west slopes of the Lewis Range.
   The Federal Highway Administration (FHWA) offers an overview of best practices which includes several repair techniques; throw-and-roll, semi-permanent, spray injection, and edge seal. The FHWA suggests the best patching techniques, at times other than winter, are spray injection, throw-and-roll, semi-permanent, or edge seal procedures. In winter, the throw-and-roll technique may be the only available option. The Council for Scientific and Industrial Research in South Africa offers similar methods for the repair of potholes.
  
  Section::::Repair.:Materials.
   BULLET::::- 2014 (Feb 11) A Hiland gas pipeline exploded about six miles south of Tioga, North Dakota. Hiland was "blowing" hydrates, ice-like solids formed from a mixture of water and gas that can block pipeline flow, out of the pipeline.
  
  BULLET::::- 2014 (Mar 14) A Northern Natural Gas Company pipeline erupted near the intersection of county roads 20 and O, about six miles north of Fremont, Nebraska. A company spokesman said, "In the summer you can tell if you've got a gas leak by vegetation, sometimes it dies in the ground."
   Similar processes can act on asphalt pavements, contributing to various forms of cracking and other distresses, which, when combined with traffic and the intrusion of water, accelerate rutting, the formation of potholes, and other forms of pavement roughness.
  
  Section::::Volumetric expansion.
   A sudden rise in air temperature is can result in the rapid melting of snow. This can create flooding issues if the snowpack has sufficient water content, and this can be significantly exacerbated by heavy rainfall and by ice jams which may have formed on area rivers during prolonged subfreezing temperatures. The re-freezing of previously melted snow creates potholes in roadways. This process is accelerated when water is melted and re-frozen multiple times. Fog is also known to occur during rapid melting of snow.
  
  Avalanches and cornices occur when significant amounts of snow falls on mountains.
  
  Section::::Freezing rain.
   When frozen in winter, the waterway crossings can be built up with auger holes to flood and thicken the crossing. The act of clearing snow quickly makes ice thicker by exposing the road directly to subfreezing air (temperatures as low as ). In the summer, after the ice melts, effects of the roads can still be seen from overhead in a bush plane, as bare strips remain on the lake floor where the ice blocked light and prevented plants and algae from growing.
   In some areas of the world, including Berlin, Germany, dropping salt is prohibited altogether except on the highest-risk roads; plain sand without any melting agents is spread instead. While this may protect the environment, it is more labour-intensive, as more gritting runs are needed; because the sand is insoluble, it tends to accumulate at the sides of the road, making it more difficult for buses to pull in at bus stops.
   At low temperatures (below ), black ice can form on roadways when the moisture from automobile exhaust condenses on the road surface. 
  
  Such conditions caused multiple accidents in Minnesota when the temperatures dipped below for a prolonged period of time in mid-December 2008. Salt's ineffectiveness at melting ice at these temperatures compounds the problem. Black ice may form even when the ambient temperature is several degrees above the freezing point of water , if the air warms suddenly after a prolonged cold spell that has left the surface of the roadway well below the freezing point temperature.
   The impact of snowdrifts on transportation can be more significant than the snowfall itself, such as in the USA during the Great Blizzard of 1978. Snowdrifts are many times found at or on roads, as the crest of the roadbed or the furrows along the road create the disruption to the wind needed to shed its carried snow. Snow fences may be employed on the windward side of the road to intentionally create a drift before the snow-laden wind reaches the road.
  
  Section::::See also.
  
  BULLET::::- Blizzard
  
  BULLET::::- Lake-effect snow
  
  BULLET::::- Snow
  
  BULLET::::- Snow removal
  
  Section::::External links.
   In early January 2010, a section of the highway between 14th and 17th streets developed an unusual problem dubbed "phantom ice" during a prolonged cold wave that kept temperatures below freezing for several days in the Atlanta region. GDOT engineers believe that heavy rain in previous months raised the water table and caused it to seep upward through joints between lanes, where it subsequently froze. Commuter traffic was stopped briefly on at least two days in order to treat it with deicing materials and inspect the freeway to determine the cause.
   In the winter of 2016/17 Portland saw freezing rain, graupel, ice storms, snow storms and extended periods of freezing temperatures, which damaged the city's roads. By the end of February 2017 municipal workers had identified more than 1,000 potholes. In 2017 the Portland Bureau of Transportation (PBOT) launched a "patch-a-thon" to fast-track road repairs, but acknowledged that repairs to some roads would not be completed until summer 2017.
   Section::::Dangers.
  
  Both types of snowsqualls are very dangerous for motorists and airplanes or generally any traveler unfortunate enough to get stuck in one. The change in conditions is very sudden, and slippery conditions and abrupt loss of visibility due to whiteouts often cause multiple-vehicle collisions. In the case of lake effect snow, heavy amounts of snow can accumulate in short periods of time, possibly causing road closures and paralyzing cities. For instance, on January 9, 2015, a localized, heavy snow squall caused a 193-vehicle pile-up on I-94 highway near Galesburg, Michigan.
  
  Section::::See also.
  
  BULLET::::- Convection
  
  BULLET::::- Shower
   Typically, hoodoos form from multiple weathering processes that continuously work together in eroding the edges of a rock formation known as a fin. For example, the primary weathering force at Bryce Canyon is frost wedging. The hoodoos at Bryce Canyon experience more than 200 freeze-thaw cycles each year. In the winter, melting snow, in the form of water, seeps into the cracks and then freezes at night. When water freezes it expands by almost 10%, pries open the cracks bit by bit, making them even wider, similar to the way a pothole forms in a paved road.
   BULLET::::- In higher rainfall areas, the increased camber required to drain water, and open drainage ditches at the sides of the road, often cause vehicles with a high centre of gravity, such as trucks and off-road vehicles, to overturn if they do not keep close to the crown of the road
  
  BULLET::::- Excess dust permeates door-opening rubber moulding breaking the seal
  
  BULLET::::- Lost binder in the form of road dust, when mixed with rain, will wear away the painted surfaces of vehicles
   A snow shed, constructed in 1950 when the road was known as US-10, formerly covered the westbound lanes, but it has been replaced by 'avalanche bridges' that stand away from the slope to allow slides to pass under the road, as of April 2014. 
  
  WSDOT maintains cameras at selected locations along the pass to monitor weather conditions. Some of these cameras can be viewed via the internet.
  
  Section::::Recreation.
   In England and Wales both Severn crossings were closed on 6 February because ice began falling from overhead gantries, affecting both the M4 and M48 motorways across the Severn Estuary; traffic was diverted into Gloucestershire and onto the M50. This was the first closure because of a weather-related incident of the second Severn crossing since the structure opened in 1996. They reopened on 10 February.
  
  The A23 between Brighton and Haywards Heath saw severe disruption on 2 February and the A27 through Brighton was closed because of the huge volume of snowfall.
  
  Section::::Effects.:Air traffic delays.
  