question: why do bridges not form potholes but normal roads do?
comment: Bridges lack what most roads have, a lively earth underneath them. Despite having many inches or sometimes even feet of packed gravel roadbed, the soil beneath undulates, heaving up in some places, and sinking away in other places. Additionally the gravel roadbed itself is susceptible to water displacement. Usually both are at work to do their best to screw up our roads. Bridges on the other hand usually have steel or concrete under the asphalt, thus are not subject to soil or displacement issues. And cement is perfectly capable of forming potholes. It's just a little less prone to than asphalt, because it must fracture first.
passages: There are three subcategories of rigid pavement overlays that are organized depending on the bonding condition at the pavement overlay and existing slab interface.
  
  BULLET::::- Bonded overlays
  
  BULLET::::- Unbonded overlays
  
  BULLET::::- Partially bonded overlays
  
  Section::::Design.:Drainage system design.
  
  Designing for proper drainage of highway systems is crucial to their success. Regardless of how well other aspects of a road are designed and constructed, adequate drainage is mandatory for a road to survive its entire service life. Excess water in the highway structure can inevitably lead to premature failure, even if the failure is not catastrophic.
   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.
   According to the US Army Corps of Engineers, pothole formation requires two factors to be present at the same time: water and traffic. Water weakens the soil beneath the pavement while traffic applies the loads that stress the pavement past the breaking point. Potholes form progressively from fatigue of the road surface which can lead to a precursor failure pattern known as crocodile (or alligator) cracking. Eventually, chunks of pavement between the fatigue cracks gradually work loose, and may then be plucked or forced out of the surface by continued wheel loads to create a pothole.
   Likewise, macadam and tarmac pavements can still sometimes be found buried underneath asphalt concrete or Portland cement concrete pavements, but are rarely constructed today.
   BULLET::::- Arkansas State Highway and Transportation Department (AHTD)
  
  BULLET::::- California Department of Transportation (Caltrans)
  
  BULLET::::- Colorado Department of Transportation (CDOT)
  
  BULLET::::- Connecticut Department of Transportation (CONNDOT)
  
  BULLET::::- Delaware Department of Transportation (DelDOT)
  
  BULLET::::- Florida Department of Transportation (FDOT)
  
  BULLET::::- Georgia Department of Transportation (GDOT)
  
  BULLET::::- Hawaii Department of Transportation (HDOT)
  
  BULLET::::- Idaho Transportation Department (ITD)
  
  BULLET::::- Illinois Department of Transportation (IDOT)
  
  BULLET::::- Indiana Department of Transportation (INDOT)
  
  BULLET::::- Iowa Department of Transportation (Iowa DOT)
  
  BULLET::::- Kansas Department of Transportation (KDOT)
  
  BULLET::::- Kentucky Transportation Cabinet (KYTC)
  
  BULLET::::- Louisiana Department of Transportation and Development (DOTD)
  
  BULLET::::- Maine Department of Transportation (MaineDOT)
   When repairing pavement affected by fatigue cracking, the main cause of the distress should be determined. However, often the specific cause is fairly difficult to determine, and prevention is therefore correspondingly difficult. Any investigation should involve digging a pit or coring the pavement and subbase to determine the pavement's structural makeup as well as determining whether or not subsurface moisture is a contributing factor. The repair needed also differs based on the severity and extent of the cracking.
   The significance of degradation scour to bridge design is that the engineer has to decide whether the existing channel elevation is likely to be constant over the life of the bridge, or whether it will change. If change is probable then it must be allowed for when designing the waterway and foundations.
   BULLET::::- Pittsburgh Fort Wayne & Chicago Railroad Bridge#1 over Calumet River
  
  BULLET::::- Pittsburgh Fort Wayne & Chicago Railroad Bridge #2 over Calumet River
  
  BULLET::::- Lake Shore & Michigan Southern Railroad Bridge#1 over Calumet River
  
  BULLET::::- Lake Shore & Michigan Southern Railroad Bridge#2 over Calumet River
  
  BULLET::::- Baltimore & Ohio Chicago Terminal Railroad Bridge over Calumet River
  
  BULLET::::- 100th Street Bridge over Calumet River
  
  BULLET::::- 106th Street Bridge over Calumet River
  
  BULLET::::- Chicago & Western Indiana Railroad Bridge over Calumet River
  
  BULLET::::- Torrence Avenue Bridge over Calumet River
  
  BULLET::::- Nickel Plate Road Railroad Bridge over Calumet River
   Section::::Definitions.:United States.
  
  In the United States, laws distinguish between "public roads", which are open to public use, and "private roads", which are privately controlled.
  
  Maintenance is becoming an increasing problem in the United States. Between 1997 and 2018, the number of existing roads too bumpy to drive on compared to roads with decent surfaces has increased by 11%, mostly due to potholes that are not being properly addressed.
  
  Section::::History.
   During flooding, although the foundations of a bridge might not suffer damage, the fill behind abutments may scour. This type of damage typically occurs with single-span bridges with vertical wall abutments.
  
  Section::::Bridge examination and scour evaluation.
   Section::::Structural integrity.
  
  What happens when a heavy truck passes over, or flood water plugs an opening with debris or overtops the structure.
  
  Section::::Habitat continuity.
  
  Passage of wildlife, particularly fish such as salmon which spawn in streams, is a design consideration as is habitat continuity. In some jurisdictions, such as Massachusetts, these considerations may be incorporated into stream crossing regulations.
  
  Section::::See also.
  
  BULLET::::- Log bridges
  
  Section::::Further reading.
  
  BULLET::::- North Atlantic Aquatic Connectivity Collaborative (NAACC)
  
  BULLET::::- "An Economic  Analysis  of   Improved  Road‐Stream  Crossings" (Adirondack  Chapter of The Nature  Conservancy  August 2013)
   BULLET::::- In Hong Kong, there was a bridge from the old Kai Tak airport to the Regal Hotel. Now that the Airport has moved ( and has been demolished ), the bridge is not used.
  
  Section::::Incomplete and damaged bridges.:Czech Republic.
  
  BULLET::::- The Borovsko Bridge, an unfinished motorway bridge from 1930s near Borovsko, part of Bernartice municipality, Central Bohemian Region.
  
  BULLET::::- There are several bridges to nowhere, started to be built as a part of extraterritorial highway Vienna-Wrocław (so-called "Hitler's highway"), which remain unfinished and unconnected to the road network.
  
  Section::::Incomplete and damaged bridges.:France.
   Only 16 months after its official opening there are potholes in the road from the bridge to the toll gates, as can be seen further on in the aforementioned video
   BULLET::::- B. Properties associated with a significant person in America's past. However, bridges significant in conjunction with their architect are to be listed under criterion C. It is possible, although unlikely, that a particular bridge may be associated with a significant person other than its designer, such as a politician or city official who advocated for its construction.
   If the upstream shear stress is less than the threshold value, the bed material upstream of the bridge is at rest. This is referred to as the clear-water condition because the approach flow is clear and does not contain sediment. Thus, any bed material that is removed from a local scour hole is not replaced by sediment being transported by the approach flow. The maximum local scour depth is achieved when the size of the scour hole results in a local reduction in shear stress to the critical value such that the flow can no longer remove bed material from the scoured area.
   FHWA advised states to inspect the 700 U.S. bridges of similar construction after identifying a possible design flaw related to large steel sheets called gusset plates, which connect girders in the truss structure. Officials raised questions as to why such a flaw would not have been discovered in over 40 years of inspections. The flaw was first discovered by Wiss, Janney, Elstner Associates, Inc., an independent consulting firm hired by Mn/DOT to investigate the cause of the collapse.
   The first major issue when considering scour is the distinction between clear-water scour and live-bed scour. The critical issue here is whether or not the mean bed shear stress of the flow upstream of the bridge is less than or larger than the threshold value needed to move the bed material.
   By Interstate standard, all bridges on the Interstate system must be fixed as to not interrupt the flow of traffic. Several bridges on the system, however, are movable:
  
  BULLET::::- I-5 crosses the Columbia River from Portland, Oregon, to Vancouver, Washington, on the Interstate Bridge, a vertical-lift bridge. The Columbia River Crossing project sought to replace this bridge until being abandoned in 2013.
  
  BULLET::::- I-110 has a drawbridge across the Back Bay of Biloxi in Biloxi, Mississippi.
  
  BULLET::::- I-64—the Hampton Roads Beltway—crosses the South Branch Elizabeth River in Chesapeake, Virginia, on the High Rise Bridge, which is a drawbridge.
   BULLET::::- Horizontal clearance: under or along a bridge shall be the full paved width of the rest of the road. Bridges longer than can be narrower, with a minimum of on both sides of the travel lanes.
  
  BULLET::::- Bridge strength: New bridges are to have at least MS 18 (HS-20) structural capacity. Weaker bridges that can continue to serve the route for 20 more years are allowed to remain.
   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
   BULLET::::- Additionally, existing bridges can remain if they have at least lanes with outside and inside shoulders. Long bridges are to have at least on each side of the travel lanes; bridge railing should be upgraded to current standards if necessary.
   Section::::Incomplete and damaged bridges.:Slovakia.
   BULLET::::- Vertical clearance: Minimum vertical clearance under overhead structures (including over the paved shoulders) of in rural areas and in urban areas, with allowance for extra layers of pavement. Through urban areas at least one routing should have clearances. Sign supports and pedestrian overpasses must be at least above the road, except on urban routes with lesser clearance, where they should be at least higher than other objects.
   Bridge to nowhere
  
  A bridge to nowhere is a bridge where one or both ends are broken or incomplete and does not lead anywhere. If it is an overpass or an interchange, the term overpass to nowhere or interchange to nowhere may be used respectively. There are three main origins for these bridges:
  
  BULLET::::- The bridge was never completed for reasons such as cost or disputed property rights.
  
  BULLET::::- One or both of the bridge's ends have collapsed or have been destroyed – e.g., by earthquake, storm, flood, or war.
   BULLET::::- North Carolina Department of Transportation (NCDOT)
  
  BULLET::::- North Dakota Department of Transportation (NDDOT)
  
  BULLET::::- Ohio Department of Transportation (ODOT)
  
  BULLET::::- Oklahoma Department of Transportation (ODOT)
  
  BULLET::::- Oregon Department of Transportation (ODOT)
  
  BULLET::::- Pennsylvania Department of Transportation (PennDOT)
  
  BULLET::::- Puerto Rico Department of Transportation and Public Works (DTOP)
  
  BULLET::::- Rhode Island Department of Transportation (RIDOT)
  
  BULLET::::- South Carolina Department of Transportation (SCDOT)
  
  BULLET::::- South Dakota Department of Transportation (SDDOT)
  
  BULLET::::- Tennessee Department of Transportation (TDOT)
  
  BULLET::::- Texas Department of Transportation (TxDOT)
  
  BULLET::::- Utah Department of Transportation (UDOT)
  
  BULLET::::- Vermont Agency of Transportation (VTrans)
  
  BULLET::::- Virginia Department of Transportation (VDOT)
  
presuppositions: Bridges do not form potholes.
corrections: Bridges can form potholes if the cement fractures first.
raw_presuppositions: Bridges do not form potholes. Bridges do not form potholes.
raw_corrections: Bridges can form potholes if the cement fractures first. Bridges can form potholes if the cement fractures first.