Roadways

IDOT partners with the Illinois State Archaeological Survey (ISAS) to maintain Historic Bridge Survey inventories to maintain an inventory of the State's Historic Bridges, which are at least fifty years old and of historical significance. 

IDOT Guidance for Photographing Historic Structures

• The Illinois Highway Information System Roadway Info & Procedure Manual defines what, why and how roadway data is collected, and explains the individual codes used for all the roadway data provided by the Illinois Roadway Information System (IRIS).
• The Illinois Highway Information System Structure Info & Procedure Manual defines what, why, and how structure data is collected, and explains the individual codes used for all the structure data provided by the Illinois Structure Information System (ISIS).
• The Illinois Traffic Monitoring Program Manual documents the current processes and strategies used throughout the state to meet the existing traffic requirements for IDOT.

• The Illinois Highway and Street Mileage Statistics publication contains information on the centerline miles totaled by IDOT District, county, pavement type, functional class, and urban areas.
  
• The National Highway System (NHS) Illinois Statistics Sheet contains mileage, Vehicle Miles of Travel (VMT), and structure statistics for roads and bridges on the National Highway System. Mileage and VMT is summarized by functional class and road system. Structure data is summarized by road system and square footage, along with totals for structurally deficient and functionally obsolete NHS structures.
  
• The Illinois Highway Statistics Sheet contains statewide mileage and VMT summary information by functional class and road system. Statewide totals as well as subtotals for the nine individual IDOT Highway Districts are displayed. Summary information about structures is also included.
• The Illinois Travel Statistics booklet contains a variety of current and historical traffic information. VMT data is summarized by IDOT highway district, county, functional class, road system, and urbanized area. While statewide travel history dates back to 1950, individual county VMT subtotals have been tabulated for the last five years. Charts displaying monthly, daily, and hourly traffic patterns are also included.
• The FY 2024 Condition Rating Survey Summary Report provides information on the condition of the highway system in categories (Excellent, Good, Fair, Poor), current and historical statistics about the amount of pavement grouped by the State of Acceptable Condition (SOAC) criteria, and the roughness (IRI International Roughness Index) by highway type and district.
• IDOT collects condition data on Interstate pavements annually and on non-Interstate pavements on a two-year cycle. Bridges receive a routine visual inspection at least every two years, except for some in good condition that are inspected on a four-year cycle. Underwater inspections are performed every five years. Other inspections may be conducted following incidents that threaten bridge stability (e.g., collisions or floods), to monitor special situations, or following new construction. The results of the most recent NHS pavement condition assessments and bridge inspections are posted annually on the TAMP Performance Reports (Performance (illinois.gov). The files contain both the State of Acceptable Condition and Federal Performance Measure results.
• The FHWA Highway Statistics publication consists of annual reports containing analyzed statistical information on motor fuel, motor vehicle registrations, driver licenses, highway user taxation, highway mileage, travel, and highway finance.
• Crash data is analyzed by IDOT continually. Summary Crash Data reports are available for public viewing. IDOT is not authorized to release individual crash reports.