Traffic signal warrants set the minimum conditions under which a traffic signal installation may be appropriate. The four-hour volume signal warrant in the current Manual on Uniform Traffic Control Devices (MUTCD) (FHWA 2009) is applied based on a set of critical vehicular volumes for different lane combinations of major and minor streets. This paper describes an effort to apply microscopic simulation to evaluate the critical volumes used in the four-hour warrant. The results show significant differences in average control delay for minor street traffic under different volume combinations, lane configurations, turning volume percentages, heavy vehicle percentages, and the number of major street lanes (four versus six lanes), most of which are not currently considered in the four-hour warrant. This finding provides some evidence of the need to possibly revise the critical design values of the current four-hour volume warrant.