I Guidelines for Right - TurnTreatments at Signalized Intersections

arterial corridor greatly impacted by strip commercial development. The data-gathering efforts consisted of extensive traffic counts and travel-time and delay studies. This enabled us to see firsthand the great congestion that was occurring on the street. At the four most-congested intersections, unequal queuing between the two through traffic lanes was observed. In all cases, the right lane’s queue appeared at least 20 percent, and up to 50 percent, longer than the left lane’s queue during the most congested hours. By comparison, the default lane utilization factor in the Highway Capacity Manuall procedures is 1.05, thus assuming the more saturated lane will carry about 5 percent more volume. Since each approach to these intersections had peak-hour right-turn volumes of 200 or more, it appeared that a right-turn lane at these intersections would measurably improve levels of service. At the same time, the Oregon Traffic Control Devices Committee was presented with a request by the City of Salem to consider the use of protected/permitted right-turn overlap phasing. A protected/permitted rightturn overlap phase is a signal indication in which the right-turn movement is displayed a green ball during a permitted phase, and a green right arrow during a protected phase. This operation can occur only if the cross-street of the subject approach has a protected leftturn phase and no U-turn is permitted. For example, an eastbound approach would be displayed circular green indications during the eastbound throughtraffic phase. During the following northbound left-turn phase, the eastbound through lanes would be displayed circular red indications. But the eastbound right-turn lane could be displayed a green right-arrow because this movement would have no conflicting movement, as long as U-turns were not permitted from the northbound leftturn lane. Currently, the Oregon Traffic Control Devices Committee has approved a right-turn overlap phase that must be “protected only” by displaying right-arrow signal indications, and prohibition of conflicting pedestrian crossings or “permitted only” with a circular green indication on a programmed-visibility signal head to limit the visibility of the right-turn signal indications to the right-turn lane. The committee referred to the city the task of studying guidelines for protected/permitted right-turn overlap phasing as well as warrants for installing right-turn lanes at signalized intersections.