To work effectively, a traffic signal system needs an appropriate signal phasing plan. A low-volume intersection will normally operate with two phases, one for the major street, and one for the minor street. A "phase" is one cycle of green, yellow, and red change intervals. As traffic volume increases, more phases may be required to give the right-of-way to left-turn movements. Each phase added to the signal operation takes time away from existing phases. The all-red interval varies by intersection width, speed limit, and vehicle length. Typically all-red interval timings range from 1 second to 3 seconds. See the BMTE calculator module to calculate all-red interval timing.