Why was a 56% column added to Table 4C-1, and will that make it more or less difficult to install a signal?
In the 1988 and previous MUTCDs, the 56% factor was neither explicitly allowed nor prohibited in the signal warrants. But many jurisdictions inferred that, when applying what used to be called the Combination Warrant (which allows a reduction to 80%) in high-speed or isolated rural community conditions (where a reduction to 70% is allowed), 70% of 80% (56%) could be used. When the warrants were in a narrative, rather than tabular, form it was possible for agencies to infer this. In the 2000 MUTCD, when the warrant values were put into tabular form, the NCUTCD consciously recommended (and FHWA decided) to not include a 56% column. Subsequently, there were objections from many agencies that had installed significant numbers of signals based on meeting the 56% volumes and now those signals were technically not compliant with the MUTCD. The 2003 edition of the MUTCD added a 56% column and described the conditions under which it may be used. This does make it easier to meet the numerical si
