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 1970’s 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 developers of commercial software products that “automate” the signal warrant analysis process most likely created formulas or equations by working backwards from plotted points on the curves and/or using “curve fitting” programs. Also, 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. Those descriptions were developed specifically to meet Section 508 of the ADA law, which requires the federal government to make accessible t
