34-45 Reid Feature minus ads

ITE JOURNAL / JUNE 2000 ARTERIAL CAPACITY PROBLEMS The function of an arterial is efficient movement of large traffic volumes over a significant distance.1 As arterial traffic volumes approach roadway capacity, delays grow rapidly at signalized intersections with significant cross-street volumes, diminishing the ability of the arterials to help traffic move effectively. Under conventional arterial roadway and intersection designs (i.e., multilane or divided highways that provide direct left-turn movements at the intersection), intersection capacity is constrained by through and left-turn conflicts at the intersection. Safety concerns and/or high turn-movement volumes often dictate protected-only left-turn phasing at arterial intersections. Protected left-turns increase delay by adding additional start-up and clearance lost times, which reduce the amount of green time that can be efficiently dedicated to arterial through movements. When conventional arterial intersections become over-saturated, a common traffic-engineering “solution” to increase intersection capacity is to lengthen the signal cycle length. Longer cycle lengths reduce the impact of “lost time” between phases and allow longer through-movement phases. However, an undesirable product of a longer cycle length is increased intersection delay and queue lengths.