Travel Time Comparisons Between Seven Unconventional Arterial Intersection Designs

Signalized intersections on high-volume arterials are often congested during peak periods, causing a decrease in through movement efficiency on the arterial. Much of the vehicle delay incurred at conventional arterial intersections is caused by high left-turn demand. Unconventional intersection designs attempt to reduce intersection delay and travel times by rerouting left turns away from the main intersection. Seven unconventional designs—the quadrant roadway intersection, median U-turn, superstreet median, bowtie, jughandle, split intersection, and continuous flow intersection designs—that could apply to a wide range of standard, four-leg intersections are compared. Previous comparisons of intersection delay and travel time between conventional designs and these unconventional designs have been piecemeal and have largely used hypothetical volumes. Simulation experiments were conducted using turning movement data from seven existing intersections of varying sizes to compare the travel time of conventional and unconventional designs fairly. Optimum cycle lengths were used for each design, and a number of factors were held constant to keep the comparisons fair. Off-peak, peak, and peak-plus-15-percent volume levels were examined. The results from the simulations showed that at each intersection one or more unconventional designs had lower total travel times than the conventional design. Whereas most of the unconventional designs showed improvement in one or more scenarios, the quadrant roadway intersection and the median U-turn designs consistently produced the lowest travel times. When considering the design of high-volume intersections like those tested, engineers should seriously consider quadrant roadway intersection and median U-turn designs where rights-of-way are available.