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16             SECTION 1                                                  ADMINISTRATIVE ISSUES



                        1.6  OVERVIEW OF MAINTENANCE PROCEDURES
                        1.6.1  Classifying the Type of Bridge
                        1. Importance: A bridge is a necessary but small part of a highway system. Its importance is
                            linked to:
                            •   The network of roads it serves
                            •   The volume of traffic it carries

                            •   Its relative importance to meet funding criteria and funding priority.
                        2. Inspection classification: For inspection purposes, many highway agencies have the follow-

                            ing classifi cations:
                            •   Inventory: A bridge included in an inventory file when it carries moving loads.



                            •   Collapsed: A bridge that once satisfied the inventory bridge definition, but is now closed
                             due to collapse.

                            •   Closed: A closed bridge that once satisfied the inventory bridge definition, but is now

                             temporarily closed for any reason except collapse. Secondary uses such as pedestrian
                             traffic may be allowed.



                            •   Abandoned: A bridge that once satisfied the inventory bridge definition, but is now per-
                             manently closed.
                            •   Deleted: A bridge which has been deleted from the inventory.


                            •   Temporary: A bridge that is used to maintain traffic during a modification or replace-
                             ment.
                        3. Functions: In the U.S., bridges are located on one of the following networks and are classi-
                            fied as such:

                            Type 1–Interstate
                            Type 2–Arterial
                            Type 3–Collector
                            Type 4–Local
                            Forty percent of all bridges serve local roads. Thirty-three percent serve interstate or arte-
                            rial highways. Interstate bridges allow higher speeds. Interstates have express lanes but are
                            thoroughfares with limited access and exits. Interstate and arterial bridges carry almost
                            90 percent of average daily traffic (ADT) for rural and urban areas. Twenty-seven percent


                            of bridges serve collectors. Collectors collect and distribute traffic between arterials and
                            local roads.
                            They are typically two lane roads and provide for shorter trips at lower speeds.
                        4. Type of traffic: Each type has special requirements for varying live load impacts. Deck

                            surfacing is made of timber, concrete, or steel deck:
                            Type 1–Highway bridges carrying vehicular traffi c
                            Type 2–Transit and railroad bridges carrying train traffi c
                            Type 3–Pedestrian bridges
                            Type 4–Equestrian bridges
                            Type 5–Airport bridges carrying aircraft
                        5. Ownership
                            Ownership governs design criteria and procedures for maintenance or reconstruction:
                            Local government owned—51 percent
                            State government owned—48 percent
                            Federal government owned—1 percent
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