Once you have calculated the lengths of the minimum green intervals, green intervals, and intergreen intervals, as well as the design flow rates and capacities for each of your phases; it is time to ask yourself whether or not your results actually work.
The first and most obvious check involves the green intervals. Check the length of the green interval for each phase. If it is not greater than the length of the phase's minimum green interval, you need to bump up the cycle length and add green time to that phase until the green interval is equal to or greater than the minimum.
The second check involves capacity. If the capacity of a particular phase is below the design flow rate for that phase, you should back-calculate the effective green time that would allow the phase to run at the design flow rate. Once again, simply increasing the cycle length and allocating more time to the green interval of the troubled phase will solve the problem.
Webster noted that the cycle length can vary between 0.75Co and 1.5Co without adding much delay, so don't worry too much about adding a second or two to the nominal cycle length.