[TDM listserv post on the Oregon DOT's changes to speed limit setting, most notably shifting to 50th percentile rather than 85th percentile]
Hi friends and colleagues,
I wanted to let you know that ODOT's new Oregon Administrative Rule around speed-setting went into effect on May 1. Review an overview of the new process https://www.oregon.gov/odot/Engineering/Docs_TrafficEng/Speed-Setting-Update-2020-05.pdf (this link is a helpful ppt overview) or review the corresponding Oregon Administrative Rule updates https://www.oregon.gov/odot/Engineering/Docs_TrafficEng/OAR-Update-Speed-Setting-2020-05.pdf for information about the change. We've also updated the Speed Zone Manual https://www.oregon.gov/odot/Engineering/Docs_TrafficEng/Speed-Zone-Manual.pdf to reflect the change. All this information lives on our Speed Zones page https://www.oregon.gov/odot/Engineering/Pages/Speed-Zones.aspx.
This represents a major step forward in our approach to posted speeds on urban arterial highways. It aligns recommended speeds with the Blueprint for Urban Design targets and anchors our technical methods around the 50th percentile speed (the typical driver) instead of the 85th percentile (the driver traveling one standard deviation faster than the norm). When choosing the posted speed, our engineering approach must document and address factors like land use context, crash history, and multimodal activity, and can also bring other elements such as user demographics and public testimony into the conversation. Rural communities will have the flexibility to use 50th percentile or the 85th.
Please feel free to reach out to me or other ODOT colleagues if you have questions about what this change means for existing plans/projects or for corridors where speed is a concern. Be aware that our Technical Services folks do not advise collecting speed data now due to COVID-related impacts on travel (which we know include increased speeding in some Oregon communities). This is new practice for all of us, so we'll be learning with you.
Thanks and hope you're all well!
Talia Jacobson, ODOT Region 1 Planning
123 NW Flanders
Portland, OR 97209