With road trip planned and route map in hand, three Florida A&M University (FAMU)-Florida State University (FSU) College of Engineering researchers made their first stop at a familiar intersection. A two-lane minor street intersected four lanes of free-flowing traffic with a divided median. Identified as a high-crash location, residents and commuters had become wary of the intersection. The researchers had an idea about how to reduce crashes at this location, but they needed more information.
Alternative intersection designs – modifying the geometry of the road to reduce the number and complexity of conflicts at intersections while still allowing traffic to flow – are a promising solution. One type of alternative intersection, the Restricted Crossing U-Turn (RCUT), has been installed in several locations in North Carolina.
FDOT has been interested in incorporating RCUTs as an option for intersections but lacked the needed data to help staff evaluate their effectiveness in context. North Carolina and other states around the country were able to help.
Defining the RCUT
An RCUT is an alternative intersection design that directs all movements from a minor street to turn right. Motorists who want to turn left or go straight through the intersection are directed to use a dedicated U-turn downstream of the intersection. The RCUT provides the major street with full access to the minor street, often including left-turn pockets. Medians provide pedestrians with safe refuge to cross. RCUTs can be signalized or controlled by stop signs depending on the location and traffic volumes. The ideal location for an RCUT is a median-divided highway where major street volumes are high and minor street volumes are low.
Before and after studies of RCUT installations have shown a reduction in the rate, frequency, and severity of crashes. Traffic engineers commonly use a count of “conflict points” – where two vehicles merge, diverge, or cross – as one means of assessing safety. While a standard or conventional intersection has a total of 32 conflict points, an RCUT typically has only 14, implying a lower crash risk. Due to the geometry and median design of an RCUT, there are few direct crossings where conflicts can occur. Crash types linked to higher injury severity, like angle crashes, also tend to be reduced in an RCUT design because of fewer crossing conflict points.
While the purpose of an RCUT ultimately is to improve safety, this design also provides operational benefits. Travel time is reduced due to only two signal phases in a signalized RCUT, instead of the four phases in a conventional intersection, which results in increased green time and reduced fuel emissions and consumption. Improved traffic flow results in greater capacity, reduced delay, and shorter queues for the major street. While these operational benefits tend to favor vehicles traveling on the major street, RCUTs improve the performance of the overall intersection.
User perception is crucial to understanding a potential RCUT location. A change in lane geometry is sometimes upsetting to users during initial public meetings. However, after installation, residents and commuters alike have perceived RCUTs positively due to improved safety and operational performance.
Casting a Wide Net: RCUT Safety Performance Data
With so many benefits, FDOT was interested in incorporating RCUTs as an option when they evaluate modifications for intersections. Their existing safety performance tool, SPICE, already compares many other intersection types. While conflict points are a good first estimate, crash models – which connect intersection features to crash types and severities – were what the agency really wanted. Crash models are vital to understanding an intersection, but the lack of RCUTs in Florida required casting their net outside of the state.
Principal Investigator (PI) Dr. Eren Erman Ozguven worked with FDOT to collect data on RCUTs throughout the United States. In total, 22 states responded with design, safety, and performance data for 202 existing RCUTs – signalized and stop-controlled. Additionally, the research team met with traffic engineers from NCDOT and observed RCUT operations throughout North Carolina. While there, the team also worked with a drone company to capture aerial video footage of several different RCUTs, so they could further identify geometric, signal, and lane characteristics.
Dr. Ozguven explained, “Outside perspectives were critical to understanding if RCUTs could be used in certain locations in Florida to improve the safety and therefore minimize fatalities and injuries found at existing intersections.”
Implementing RCUTs in Florida
The information provided by other state agencies proved valuable for the research team in developing a model for signalized and stop-controlled RCUTs. These models mathematically predict the effect an RCUT will have on the safety performance of the intersection, known as a safety performance factor (SPF).
Many variables of crash data were investigated to create these SPFs, including crash type and severity, and other traffic, geometric, and environment-related variables. These SPFs were then added to the SPICE tool so FDOT can evaluate RCUTs as an option. As FDOT State Traffic Services Program Engineer Alan El-Urfali explained, “We now have a more robust, more reliable, and researched-based analysis for understanding RCUTs in terms of safety performance.” This comprehensive method provides structure when FDOT engineers and planners analyze intersection safety, while also providing justification for implementing new RCUTs.
Does this mean that RCUTs are going to be popping up in Florida? With the data from existing RCUTs around the country and the newly created SPFs fully integrated into FDOT’s SPICE tool, the time is right. Dr. Ozguven stated, “At this point, Florida has started designing and constructing RCUTs. I am assuming this is something that will be considered from this point on.”
Alan El-Urfali is optimistic, “Once we have more RCUTs implemented, we can monitor their performance and update our SPFs with data specific to Florida.” Someday soon, those researchers will return to that same high-crash, four-lane, stop-controlled intersection and find it transformed into a safer, innovative alternative intersection. And, just maybe, it will be an RCUT.