The term infrastructure refers to a wide variety of supportive structures, ranging from drainage systems to electric substations. Our coverage of the subject is primarily concerned with railroads, streets, alleys, expressways, sidewalks, and bridges. Here we take a closer look at an unsung part of the built environment that makes daily life possible.

• Long Lost Loop Lanes: Street necrologies, part 2.
  

• Bridge Out For Good: Five 'lost' vehicular bridge crossings over the Chicago River.
  

• The Extension and Removal of Ogden Avenue: The disappearing thoroughfare.
  

• South Western Avenue Improvement: An intact and impressive Art Deco style streetscape.
  

• Disused Turnarounds: Former trolleybus and streetcar loops.
  

• Our Historic Subway Stations: Station design of the State and Milwaukee-Dearborn subways.
  

• Wood Block Alleys: Rotting remnants of early street-paving technology.
  

• B&O’s Original Chicago Entry: Remnants of the Baltimore and Ohio Railroad's Brookdale Spur.
  

• Lake Shore Drive Redux: A brief history and remnants of reconfigurations.
  

• Tiny Streets: The 16 shortest streets in the city.
  

• 312 ‘72: Street necrologies, part 1.