Safety Evaluation of Signalized Restricted Crossing U-Turn Intersections

Chapter 1. Introduction

Background on Study

The Federal Highway Administration (FHWA) established the Development of Crash Modification Factors (DCMF) program in 2012 to address highway safety research needs for evaluating new and innovative safety strategies (improvements) by developing reliable quantitative estimates of their effectiveness in reducing crashes. The goal of the DCMF program is to save lives by identifying new safety strategies that effectively reduce crashes and promote those strategies for nationwide implementation by providing measures of their safety effectiveness and benefit–cost (B/C) ratios through research. State transportation departments and other transportation agencies need to have objective measures for safety effectiveness and B/C ratios before investing in new strategies for statewide safety improvements. Forty State transportation departments provide technical feedback on safety improvements to the DCMF program and implement new safety improvements to facilitate evaluations. These States are members of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study, which functions under the DCMF program.

The restricted crossing U-turn (RCUT) intersection strategy was selected for evaluation as part of this effort.

Background on Strategy

An RCUT is defined as a three-approach or four-approach intersection where minor street left-turn and through movements (if any) are rerouted to one-way downstream U-turn crossovers. RCUTs are also known as superstreets, J-turns, reduced conflict intersections, and synchronized streets. Figure 1 shows a schematic of a signalized RCUT with four approaches. Ten States have collectively installed at least 50 RCUTs since the late 1980s.⁽¹⁾ At least five States have installed signalized RCUTs where the major street crossover(s) and U-turn crossover(s) are controlled by traffic signals. Studies have shown RCUTs to have advantages over traditional intersections in terms of travel time and delay, signal progression, pedestrian crossing, and transit service.⁽¹⁾

There are several theoretical reasons to believe that RCUTs have the potential to reduce crash frequency and severity compared to conventional intersections. First and foremost, RCUTs reduce the number of conflict points, as shown in table 1 (and illustrated in figure 2 and figure 3). The number of conflict points at an intersection is commonly thought to be related to the number of crashes, and the RCUT design reduces the number of decision points for drivers. This is also true for pedestrian movements. At signalized four-approach RCUTs, pedestrians should experience conflicts when crossing a major street only if a driver violates a red signal or if the pedestrian jaywalks. In addition, the types of vehicle-to-vehicle conflicts change at an RCUT compared to conventional intersections. This includes fewer right-angle conflicts, which generally result in more severe crashes. There is also more distance between conflict points at an RCUT compared to conventional intersections, which provides drivers more space and time to perceive and react to potential safety issues.

There are several unique elements of signalized RCUTs that are expected to improve intersection safety.⁽¹⁾ For example, the signal progression possible along an RCUT corridor can help manage speed and decrease stops, which may produce safety benefits. RCUT signals may function using as few as two phases, simplifying related decisionmaking and reducing opportunities for signal violations and traps. Additionally, most RCUTs feature medians to divide directions of traffic along the major road, potentially resulting in fewer opposite direction head-on and driveway-related crashes sometimes associated with these types of corridors.

Conversely, the following RCUT elements could negate or outweigh the expected safety benefits as compared to a traditional intersection:⁽¹⁾

• Left-turn and through vehicles from the minor street travel longer overall distances at an RCUT—to the downstream U-turn crossover and back—which could lead to an increase in the number of crashes related to distance traveled (e.g., animal crashes). U-turn crossovers at signalized RCUTs are typically 500 to 800 ft from the main intersection, so total added distances traveled are not insignificant.
• The movements from the minor street—where a right-turn/U-turn combination replaces a direct left-turn left or straight through—may be counterintuitive to unfamiliar drivers and may lead to maneuvers that could result in crashes.
• Signalized RCUTs with two or more lanes in the crossovers or from minor streets involve side-by-side turns, which could lead to sideswipe crashes.
• RCUTs have more signals (two at a three-legged intersection and four at a four-legged intersection) than a conventional intersection with one signal, which may contribute to rear-end crashes.

Three major studies with relatively large crash samples and accepted analysis methods have been published in recent years analyzing the installation of unsignalized RCUTs at sites that previously were conventional unsignalized intersections.⁽¹⁾ The percentage decreases in crashes, shown in table 2, were statistically different from 0 at the 95-percent level or greater. These studies suggest that unsignalized RCUTs can be effective safety countermeasures and offer promise that signalized RCUTs may also be effective safety countermeasures.

More recently, RCUTs were featured in the FHWA Every Day Counts 2 program, as well as in projects to develop informational videos, capacity models for the Highway Capacity Manual, and informational guides for planners and designers.⁽²⁾ Some States have also sponsored meaningful research on RCUT operations, and, as previously discussed, thoroughly researched the safety of unsignalized RCUTs. Although research and experience support the implementation of signalized RCUTs to improve traffic operations, research was needed on the safety effectiveness.

The objective of this evaluation was to develop a crash modification factor (CMF) for the replacement of a traditional signalized intersection with a signalized RCUT. The evaluation was also intended to conduct a qualitative analysis of crash data at signalized RCUTs to provide information to designers on expected crash patterns and trends. The evaluation considered 28 signalized RCUT sites across 5 States to understand its safety effectiveness. Finally, the evaluation provided a range of B/C ratios for signalized RCUT installation. Achieving these objectives should help transportation agencies select appropriate locations to install signalized RCUTs to improve intersection safety and operations.