FLASHING YELLOW ARROW: NOVELTY OR NASCENCY?

Almost every traffic engineering decision involves a balance between safety and efficiency, and this holds true in the selection of phasing for left turns. Permitted-only left turn phasing gives the most freedom of choice to left-turning traffic, but that freedom of choice often leads to increased crash rates. Also, during some time periods, permitted left turns may not provide sufficient capacity for left turn volumes. Exclusive-only phasing offers the most protection, but usually at the cost of lower overall efficiency and higher driver frustration, particularly during off-peak periods. Exclusive/permitted phasing can offer the best, and worst, of both worlds. Most practitioners agree on the optimal signal displays for exclusive-only or permitted-only left turns. However, there is less agreement on the best display for exclusive/permitted left turns. The most common display consists of a circular green in a five-section arrangement, portrayed in the Manual on Uniform Traffic Control Devices as type (m) or type (s). Unfortunately, it is the most misinterpreted display by drivers, as evidenced by field observations and driver surveys. As a result, many alternative displays have been attempted. This report describes a promising alternative display: the flashing yellow arrow.