Travel Time Comparisons Between Seven Unconventional Arterial Intersection Designs

Abstract

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.

Barriers to Implementation of Unconventional Intersection Designs

“…Unconventional designs vary in right-of-way needs. Although some use just as much right-of-way as conventional solutions, many offer the possibility to add capacity without the need to increase right-of-way in traditional locations (Reid & Hummer, 2001;S. Siromaskul, personal communication, June 27, 2011).…”

“…Even strong advocates of UIIDs admit that unconventional designs solve specific problems but are not the cure for all traffic problems (Autey et al, 2010;Hummer & Reid, 1999;Reid & Hummer, 2001;Sangster & Hummer, 2010;H. Young, personal communication, June 24, 2011).…”

Multi‐objective analysis of using U‐turns as alternatives to direct left turns at two‐way stop‐controlled intersections

“…The use of right turn followed by U‐turn (RTUT) treatments reduces conflict points and simplifies driving tasks at TWSC intersections . However, the treatments may also result in increased system travel time as drivers need to make U‐turns at a downstream mid‐block median opening . From a more general perspective, traffic design treatments affect system performance in many different ways, including safety, traffic operations, environment, and so on.…”

“…The use of right turn followed by U-turn (RTUT) treatments reduces conflict points and simplifies driving tasks at TWSC intersections [1][2][3][4][5][6][7][8][9][10][11][12]. However, the treatments may also result in increased system travel time as drivers need to make U-turns at a downstream mid-block median opening [13][14][15][16][17][18].…”

Capacity Matching Based Model for Protected Left Turn Phases Design of Adjacent Signalized Intersections Along Arterial Roads

“…However, in order to alleviate traffic congestion and avoid spill back at high-density signalized intersections due to high traffic demand, left turn forbidden has been viewed as an efficient method. Prohibiting the offending left turn can be done in different ways; e.g., with median U-turns [9][10], jughandles [11], superstreets [12], split intersection, quadrant roadways, and bowties [13]. To some extent, these strategies can be effective because they eliminate the conflicts between the left turn and through movement, decrease the lost time, and add the number of through lanes, thereby solving the problem.…”