Guest Post by Bryant Ficek, PE, PTOE, Vice-President at Spack Consulting
Recently we announced the release of a new traffic signal and stop sign warrants spreadsheets that included warrants 1 – 3. A key driver for us to develop easy-to-use warrant analysis spreadsheets was we saw a need to get to warrant analysis data quickly and affordably.
After our first warrant spreadsheet was well received by our customers, we develop our second Warrants Analysis spreadsheet covering the rest of the warrants. This provides our readers and clients with a choice of tools to examine traffic signal and multi-way stop warrants:
- Warrants 1-3 and Multi-Way Stop Spreadsheet: simple Excel spreadsheet, which covers about 95% of warrant analysis traffic engineers encounter
- Warrants 1-9 and Multi-Way Stop Spreadsheet: simple Excel spreadsheet covering all the warrants
Both spreadsheets were developed based on the guidelines of the Manual on Uniform Traffic Control Devices (MUTCD) and I personally reviewed the formulas and methodology to ensure the spreadsheets accurately reflected the numbers and intent of the warrants. Each version of our Warrant Analysis spreadsheets also includes updated graphs for the 4-hour and peak hour vehicular volumes, pedestrian volumes and highway-rail crossings, as well as the addition of the 56% volume thresholds. With nine warrants and the multi-way stop warrant, there’s a lot of technical information to understand. In my quest to provide the most accurate information for these tools, I came across a couple answers to Frequently Asked Questions that makes me wonder about the underlying MUTCD process:
- How can I obtain the formulas on which the curves in the graphs for signal warrants 2 (four-hour warrant) and 3 (peak hour warrant) are based? “The formulas are not readily available. Those graphical MUTCD signal warrants were based (loosely) on modeling and simulation research in the 1970s that developed a large number of curves. The curves that ended up in the MUTCD don’t exactly match what’s in the research report, as a result of massaging that was done to obtain consensus agreement on the new warrants from the practicing traffic engineering community at that time. … the HTML version of Part 4 on FHWA’s MUTCD website has tabular formatted charts of the graphs that are part of the Section 508-compliant “text descriptions” of the figures and graphics. … However, it must be recognized that these plotted point numerical values have no official or legal basis and are just estimates provided for user information only.”
- Where did the numbers for the Pedestrian Volume and School Crossing signal warrants come from? “The Pedestrian Volume warrant (currently Warrant 4) has been in the MUTCD since the 1935 edition. In the 2009 edition, the warrant criteria and numbers for this warrant were revised based on research as documented in the 2006 report “Improving Pedestrian Safety at Unsignalized Pedestrian Crossings” (TCRP Report 112/NCHRP Report 562.). The School Crossing warrant (currently Warrant 5), was added to the MUTCD in 1971. No information is available on how that warrant was developed or what it was based on, although there may have been some supporting research in the late 1960s or early 1970s.”
My laymen terms breakdown – the warrants are based on old studies from before I was born, and that they don’t reflect today’s travel habits. I have great confidence that our spreadsheets accurately reflect the warrant information and thresholds listed in the MUTCD. But maybe it’s time the Federal Highway Administration’s MUTCD Team started a comprehensive review of the traffic signal warrants that reflects today’s environment rather than the time before Apple® and Microsoft® were companies.