Illinois Department of TransportationPosted Structures. This item identifies a structure on the system of highways not approved for travel of tractor/semitrailer loads of 80,000 pounds and specified wheel bases. This information is used by the trucking industry to safely move vehicles with legal size loads. This item can be obtained from the Designated State Truck Route System Map. If in question, contact the Central Bureau of Urban Program Planning. Legal Load Structures. This item identifies a structure on the system of highways approved for legal travel of tractor/semitrailer loads. This information is used by the trucking industry to safely move vehicles with overweight permits, which can't cross these structures legally. This item can be obtained from the Obstructions and Restrictions Map. For details: Structure Information and Procedures (SIP manual) The SIP manual has been developed through a cooperative effort within the Department between the Division of Highways and the Office of Planning and Programming. IDOT and its Divisions and Offices are committed to maintaining the structure information system at a high level. This commitment is not only to satisfy NBIS requirements, but also to provide an excellent working tool in managing the bridges and other structures as they relate to the overall transportation system in Illinois. In the interest of the traveling public's safety and convenience, this commitment remains a high priority for the Department. Note: Data is daily updated.ArcGIS DynamicMapLayerhttps://hub.arcgis.com/datasets/00c7751daa9d454fab10aefe8f3801c1_75engIllinois DOT Open Data PortalPublicDesignated Truck Routes - Locally Maintained Posted Structures [Illinois]Web servicesIllinoisLast Modified: 2026-01-08