The Safety Priority Index System is a method originally developed in 1986 by the Oregon Department of Transportation (ODOT) for identifying potential safety problems on state highways. SPIS complies with the Federal Highway Safety Improvement Program (HSIP) and has been accepted by the Federal Highway Administration (FHWA) as fulfilling the requirements of the HSIP.
When Oregon began developing its Safety Management System in response to the 1991 ISTEA, it identified SPIS as one of several essential building blocks. SPIS has been recognized as an effective problem identification tool for evaluating state highways for segments with higher crash histories.
Several modifications to SPIS have been implemented over the years. Following the study, “An Evaluation of the Safety Priority Index System (SPIS),” completed by Dr. Robert Layton of the Transportation Research Institute at Oregon State University modifications were implemented in the 1998 SPIS reports. In 2005 the programs were rewritten in response to changes to the Crash Database, improvements to the reports were incorporated. It is expected to rewrite the SPIS programs again in 2009 to include all public roads in Oregon (not just state highways).
Additionally in 2010 ODOT undertook adding off-state highways (city and county roads) to the SPIS. Originally the SPIS only include state highways. A process was developed and piloted in 2012 to include both on-state and off-state highways into SPIS using a Geographic Information System as a basis for SPIS process. ODOT was able to calculate SPIS values for most of the functionally classed roads which include traffic volume information. So not all public roads are included in the SPIS but most of the well traveled roads are included, all those that are functionally classed roads with traffic volumes attached.