Targeting the Crosshairs
States across the country are using tailored, systemic approaches to make intersections safer.
Crashes at intersections are one of the leading causes of highway fatalities. In 2014, intersection crashes alone resulted in 8,664 fatalities out of the 32,675 total roadway deaths that year. As a means to address traffic-related fatalities and injuries on the Nation’s roadways, the Federal Highway Administration’s Office of Safety employs a focused approach to safety. This approach is built around three technical focus areas--roadway departures, intersections, and pedestrians/bicycles--and prioritizes resources and efforts to help States and local agencies address their road safety needs. More specifically, the Intersection Safety Program focuses on the many variables that influence safety at intersections, from behavioral factors and special users to intersection design and facility type.
One of the key tools that falls under this program is the Intersection Safety Implementation Plan (ISIP), which can be instrumental in helping transportation agencies reduce intersection-related traffic injuries and fatalities. States develop ISIPs as a way to include intersection safety in their Strategic Highway Safety Plan, either as a standalone emphasis area or integrated across various emphasis areas. Although a State’s Strategic Highway Safety Plan might identify some strategies for improving intersection safety, the ISIP establishes more detailed implementation activities, countermeasures, strategies, deployment levels, implementation steps, and required funding.
“The ISIPs can become the blueprint for advancing intersection safety across a State,” says Tim Taylor, safety engineer in the FHWA Resource Center. “It’s a proven approach to achieve incremental safety improvements to hundreds of intersections in a relatively short time. Eventually, enough small safety improvements can begin to have a profound cumulative impact.”
Identifying Barriers and Opportunities
Since 2012, FHWA has engaged with staff from State departments of transportation that have ISIPs through both one-on-one and peer group discussions to hear about their experiences and lessons learned. Through these discussions, FHWA officials realized that States faced similar issues, but their solutions were as varied as the States themselves.
FHWA even found that some DOTs were employing strategies that could address an issue reported by a different State. For example, States often cite limited data as one of the most common barriers to developing an ISIP. The Texas Department of Transportation (TxDOT) is working with local agencies to address this issue--a strategy other States might be able to replicate. FHWA’s goal is to create more awareness of various approaches to encourage others to either develop or update an existing ISIP.
Traditionally, States implement intersection improvement projects at locations with the greatest number of crashes (the hotspot approach) or by deploying countermeasures at all at-risk locations (the systemic approach). The systemic approach deploys countermeasures at locations with the greatest risks for crashes rather than at the locations of actual crashes.
|National Fatalities Between 2010
|Data from FHWA’s Roadway Safety Data Dashboards show the breakdown of national fatalities between 2010 and 2014 for three main focus areas: roadway departure, pedestrian/bicycle, and intersection.|
The risk factors at intersections are associated with focus crash types and facility types. For example, risk factors associated with angle crashes (focus crash type) at unsignalized intersections (focus control type) along rural, two-lane roads (focus facility type) could include visibility on the approach to the intersection; conspicuity of the intersection; sight lines and distances between legs of the intersection; and presence, condition, types, and sizes of signs and pavement markings.
To advance the systemic approach further--for intersection safety and other priority areas--FHWA developed the Systemic Safety Project Selection Tool. The tool provides transportation agencies with step-by-step guidance on conducting a systemic safety analysis.
Many States are adding a systemic component to their Highway Safety Improvement Programs. The States range in size, number of roadway miles owned, and progress. Yet their stories--from development to implementation and evaluation--highlight the notion that all States can apply and adapt the ISIP process to their needs.
|Understanding the Systemic Approach to Safety Planning|
The systemic approach to safety is a three-pronged approach: (1) analyze systemwide data to identify a problem, (2) look for similar risk factors present in severe crashes, and (3) deploy one or more low-cost countermeasures based on the risk factors to address the underlying circumstances contributing to crashes.
FHWA developed the Systemic Safety Project Selection Tool to assist transportation agencies in conducting systemic safety planning. The tool provides a step-by-step process and guidance for determining the distribution of safety countermeasures using a systemic versus hotspot approach. Even States with limited data can use this tool, because they can tailor it to fit the available data.
The tool is available at http://safety.fhwa.dot.gov/systemic.
|Process for Developing an ISIP|
Developing an ISIP
As is true with many plans, the development stage is the most important because it lays the groundwork for the future. One of the earlier documents on using a systemic approach, FHWA’s Intersection Safety Implementation Plan Process (FHWA-SA-10-010), provides a template for developing an ISIP. The template details the activities, countermeasures, strategies, deployment levels, implementation steps, and funding scenarios needed to advance intersection safety. From setting a goal for the reduction of intersection crashes to developing a draft plan, the actionable steps detailed in the document set the stage for future success and enable States to anticipate and plan for future issues.
Several States with ISIPs noted that early buy-in from decisionmakers and integration with other statewide plans were essential to the success of their ISIPs. One strategy to strengthen the support on a statewide level is to integrate the ISIP with the Strategic Highway Safety Plan or other similar statewide planning documents. Several States--Mississippi, Missouri, and North Carolina, among others--specifically identified intersection crashes as an emphasis area in their Strategic Highway Safety Plans.
|Intersection Crashes in Texas|
|Initial analyses of data on fatal/incapacitating injury (KA) crashes in the five largest urban regions in Texas by area type and traffic control revealed that State and local urban signalized intersections had the most significant overrepresentation when comparing the proportion of total intersections having a crash to the proportion of KA crashes. Therefore, TxDOT focused its ISIP on those locations.|
For example, in Tennessee, intersection safety is a subset of the State’s Infrastructure Improvements Emphasis Area, which is included in its Strategic Highway Safety Plan.
Similarly, Florida found that integrating the ISIP into its Strategic Highway Safety Plan was a useful strategy for advancing low-cost countermeasures into the plan. This, in conjunction with a statewide coalition focused on intersections and roadway departure, has driven implementation.
Florida’s neighbor is another example: Before the Georgia Department of Transportation (GDOT) finalized its plan in 2010, the State had established a strong partnership with the Governor’s Office of Highway Safety--a relationship that established engineering as a key piece of the State’s Strategic Highway Safety Plan and enabled seamless integration of the ISIP.
An ISIP is a data-driven plan, and the systemic approach to intersection safety requires accurate and up-to-date roadway, crash, and other data files. Many transportation agencies that own a large portion of roadway mileage report having strong roadway data systems, but they still face many hurdles with crash data, such as identifying and filling gaps and the timeliness of data.
For example, TxDOT initiated its ISIP in 2015 using its robust Crash Records Information System® as the basis for prioritizing projects. Once the TxDOT staff members identified the gaps in data, they worked with other transportation agencies at the State and local levels to develop strategies to address the issues. The efforts in Texas have strengthened both the data systems and the relationships with local agencies.
“Crash data currently drive the effectiveness of our ISIP, and we will continue to collect roadway characteristic data from the local transportation agencies and [metropolitan planning organizations],” says Carol Rawson, director of traffic operations with TxDOT. “By providing traffic volumes and other roadway characteristic data to TxDOT in a timely manner, our local partners recognize the benefit of obtaining additional ISIP dollars in the future.”
Various Approaches By States
Some States continue to grow awareness of the need for ISIPs and supporting data, but other DOTs with limited ownership of intersections are still debating the merits of a statewide intersection plan. Not in Pennsylvania, however. The Pennsylvania Department of Transportation (PennDOT) is a decentralized agency, but it integrated an ISIP with its Highway Safety Improvement Program policies and funding procedures during the planning phases, which ties implementation to funding. PennDOT districts receive Highway Safety Improvement Program funding, and they are responsible for implementing the countermeasures. The districts use the ISIP to confirm locations and countermeasure packages, and throughout the process, they work closely with the metropolitan and rural planning organizations as they implement the systemic safety improvements at intersections involving State highways.
By integrating the ISIP within the Strategic Highway Safety Plan and detailing an implementation strategy, PennDOT was poised for action when the funding became available. However, PennDOT exhausted its project list more quickly than anticipated after proceeding with mostly low-cost projects. PennDOT’s next task is to determine how to continue implementing the systemic approach while maintaining an up-to-date project list within the ISIP.
The Missouri Department of Transportation (MoDOT) took a slightly different approach in developing its ISIP, providing a degree of flexibility that could be useful to States like Pennsylvania. As John Miller, traffic liaison engineer with MoDOT, explains, “Missouri adopted most of the intersection plan, with the exception of the timeline to implement. This allows the plan to be flexible and change as the data changes.” Miller added that the process provided insight into how to use the systemic approach for intersections, a true benefit for the State.
|Translating ISIPs Into Policy|
Although some States may not be progressing with implementation as quickly as desired, they have used the ISIP documentation as an opportunity to develop and implement statewide policies.
For example, MoDOT adopted a signal enhancement effort as part of its signal maintenance cycle to add reflectorized backplates, adjust clearance intervals to be in compliance with the Institute of Transportation Engineers’ formula, and if necessary, limit the use of late-night flashing operations. The maintenance schedule also evaluates existing signal heads for inconsistencies with MoDOT standards.
Similarly, the South Carolina Department of Transportation (SCDOT) uses its 2008 intersection plan as a blueprint for implementation and has not had to revisit or revise the plan in order to establish updated project lists.
Putting Plans Into Action
Efforts to translate planning into real action in the form of projects vary widely among the States with formal ISIPs as well as those with informal intersection plans that are integrated into other documents. The implementation strategies reported by the States include partial systemic, corridor systemic, and full systemic approaches. The progress in some States has been more limited because of uncertainty about how far and how quickly to proceed.
Partial systemic treats locations with low-to-moderate crash histories, with a focus on widespread deployment of only low-cost improvement packages. The corridor systemic approach is narrower and focuses on multiple intersections with low-to-moderate crash histories along an extended distance of roadway. The third approach--full systemic--treats intersections entirely on risk characteristics identified through rigorous safety data analysis.
After completing an ISIP in 2009, the Mississippi Department of Transportation (MDOT) used the existence of the plan to add intersections as a critical emphasis area to an update of its Strategic Highway Safety Plan. This was an important step that connected ISIP-related projects to funding opportunities through the Highway Safety Improvement Program. However, both the systemic approach and some of the countermeasures were new to Mississippi at the time. MDOT proceeded with implementation in a more conservative fashion by treating a smaller number of intersections with the low-cost countermeasures outlined in the ISIP, including splitter islands, enhanced signing and pavement markings, and flashing beacons. In addition, MDOT has constructed J-turns at multiple locations (both in-house and as contracted projects) since 2009. Results to date have been positive, and MDOT continues to construct J-turns with more planned into 2017. The DOT also will implement a larger scale systemic deployment of low-cost intersection countermeasures in late 2016.
States with ISIPs commonly report progress with the partial systemic approach--treating some locations with low-to-moderate crash histories, as opposed to only those meeting high crash thresholds. Here, the focus is on widespread deployment of only low-cost packages of improvements, consisting mostly of enhancements to traffic control devices such as oversized signs, wider pavement markings, and traffic signal backplates with retroreflective borders. This partial systemic approach may start slowly, as evidenced in some of the State examples that follow.
In Tennessee, after the DOT completed an ISIP in 2007, progress stalled as TDOT staff consulted peers in other States to seek ideas on how to proceed. After learning more about efforts in other States, TDOT staff developed an intersection checklist and focused on intersections with 8 or more crashes from a list of more than 1,700 intersections identified for sign and marking improvements.
In Louisiana, the transportation department completed its ISIP in 2008, but funding for projects was not immediately available. Fortunately, the U.S. Department of Transportation’s Rural Safety Innovation Program provided a one-time grant opportunity in 2008. USDOT selected a proposal by the Louisiana Department of Transportation and Development (LA DOTD) to fund the construction activity for 104 intersections identified in the ISIP. One of the lessons learned from Louisiana is that an ISIP can be a source for shovel-ready safety improvements when additional funding becomes available, or as fill-in projects for unobligated Highway Safety Improvement Program funds.
SCDOT was one of the first agencies to act aggressively on its ISIP using the partial systemic approach. The State focused on the widespread deployment of the low-cost treatment packages for stop-controlled and signalized intersections. The original ISIP identified more than 2,000 intersections for treatment. With funding set aside for deployment, SCDOT improved 700 intersections initially. Lessons learned during the first wave of deployment informed SCDOT’s next steps, and the improvements to the next approximately 1,500 intersections that followed.
“The systemic approach for the data analysis allowed SCDOT to clearly define our safety target where over 40 percent of intersection-related crashes were occurring at only 2 percent of State-owned intersections,” says Joey Riddle, safety program engineer with SCDOT.“From [there], a systemic implementation allowed us to fast-track our safety improvements by condensing the typical installation timeframe from 20 years to just 3 years.”
Beyond a Partial Systemic Approach
The corridor systemic approach picks up where the partial systemic approach leaves off. The corridor approach is based on consistent treatment of multiple intersections along an extended distance of roadway with low-cost enhancement packages. Simply, when multiple intersections identified with low-to-moderate crash histories are located along a defined corridor, the transportation community deems that corridor to be a higher risk. In addition, this approach takes into account not only the safety performance, but also mobility and operational performance, adjacent land uses, and context.
Both Georgia and Missouri were able to use the corridors identified in their respective ISIPs to implement innovative projects in intersection design. Both States implemented unsignalized, restricted crossing U-turn intersection designs--also known as J-turns--as corridor improvement projects. The J-turn design is a proven safety treatment for high-speed rural, multilane, divided highways with at-grade intersections. The design has the added advantage of maintaining a high degree of access to minor crossing routes and adjacent properties. Both GDOT and MoDOT replaced several two-way, stop-controlled intersections with J-turns to reduce severe crash scenarios.
In Ohio, the corridor systemic approach was the basis for retiming yellow change and red clearance intervals for traffic signals following the guidance provided in the Institute of Transportation Engineers’ Traffic Control Devices Handbook. Ohio implemented the retiming along 35 corridors.
The third implementation strategy is the full systemic approach, which differs from the first two categories in that it calls for treating an intersection entirely based on risk characteristics identified through the rigorous analysis of safety data. Because the systemic approach identifies risk factors, there is a need to correlate characteristics of various types to the locations having crashes.These characteristics include traffic operations (for example, traffic volumes, traffic control type, traffic signal phasing, approach speeds), geometrics (for example, number of lanes, number of approaches, median presence and width), land use (for example, rural/urban, driveway presence and density), and others (for example, lighting, pavement condition). The most commonly cited barrier to using the full systemic approach is a lack of data, mostly an inventory of such intersection elements.
However, the growing familiarity and experience with the partial systemic and corridor systemic approaches is driving an interest in some States to pursue a full systemic approach as better data become available.
Evaluating Impacts On Safety
Evaluation is a vital part of any safety program, and ISIP projects are no different. However, the widespread nature of some systemic strategies and improvements can make it more difficult to determine cause and effect compared to typical site-specific safety analyses.
For example, the Florida Strategic Highway Safety Plan set a goal for achieving a 5-percent annual reduction in highway crash-related fatalities and serious injuries. The State met that goal during the period following completion of its ISIP, but FDOT was unable to link the decrease as a direct result of intersection improvements. Nonetheless, FDOT staff took the necessary steps to incorporate many of the low-cost safety improvements into Florida’s highway standards and policies for all projects.
Fortunately, some States have been able to evaluate the results of their ISIP efforts. The Louisiana deployment described earlier benefited from an evaluation component integrated into the grant program. The evaluation focused on the stop-controlled treatments [such as those generally described in FHWA’s Low Cost Safety Enhancements for Stop-Controlled and Signalized Intersections (FHWA-SA-09-020)] and used techniques and models from the American Association of State Highway and Transportation Officials’ Highway Safety Manual. It compared 36 treatment sites and 7 untreated sites with 4 years of before data and 2 years of after data. The results were clear. For three-legged, stop-controlled rural intersections, severe (serious injury and fatal) crashes saw a 56-percent reduction. Four-legged, stop-controlled rural intersections showed a reduction of 64 percent in severe crashes.
The experience in South Carolina has been the subject of an ongoing assessment under the Evaluation of Low Cost Safety Improvements Pooled Fund Study. This empirical Bayes evaluation encompasses a 10-year timeframe (2005 through 2014), with low-cost treatments at 84 signalized intersections and 434 stop-controlled intersections. Results for the signalized intersection treatments show a 10.7-percent reduction in fatal and injury crashes and an 11.6-percent reduction in right-angle crashes, both at a 95-percent confidence level. Project evaluators found a 4.5-percent reduction of total crashes at the 90-percent confidence level as well.
Results for the stop-controlled intersection treatments show an 8.3-percent reduction in total crashes, a 10-percent reduction in fatal and injury crashes, 6.7-percent reduction in rear-end crashes, 5.9-percent reduction in right-angle crashes, and 11.1-percent reduction in nighttime crashes. All results for stop-controlled intersections are statistically significant at the 95-percent confidence level with small standards of error.
Although there are marked differences between the results of the two evaluations, it is important to note the difference in the datasets. The South Carolina sample is statewide and largely reflects sites with low-to-moderate crash histories. The Louisiana sample includes fewer sites with more moderate-to-high crash histories. Although the expected crash savings per location may not be as great as with other, higher cost treatments (for example, converting a conventional intersection to a roundabout), the low cost of these treatments means States can treat many more locations, while still providing a competitive, positive benefit/cost ratio.
SCDOT’s Riddle reemphasizes this point. “Systemic upgrades through a larger statewide contract ensured uniformity of statewide implementation, gained administrative efficiencies, and realized lower pricing through economy of scale and leveraging our resources,” he says.
Using Feedback to Move Forward
The States with ISIPs that provided feedback to FHWA and shared their lessons learned varied in terms of system size and organizational structure. Each also experienced unique organizational challenges. Despite these differences, those that demonstrated the most success from their ISIPs managed to adapt and tailor them to meet immediate needs within their respective States.
For example, some States reported using the ISIP as a prescriptive document that identifies specific project locations and details the countermeasures. Other States have taken a more flexible approach, using the ISIP to inform changes to policies and standards, or informing safety improvements to projects scoped for other reasons.
All the States that provided feedback agreed that ISIPs serve a valuable purpose in introducing the concept of systemic approaches. They also inspire further ideas on how to link Strategic Highway Safety Plans to tangible outcomes funded by Highway Safety Improvement Programs.
Matthew Albee is a transportation analyst at VHB with experience in highway safety. He has a B.S. in civil engineering from North Carolina State University.
Kara Peach is a transportation planner at VHB with experience in highway safety and transportation planning. She has a B.A. from Indiana University and an M.A. from the University of Iowa.
Jeffrey Shaw, P.E., is the intersections program manager with the FHWA Office of Safety. He has a B.S. in civil engineering from the Illinois Institute of Technology.
Jonathan Soika, P.E., is a senior transportation engineer at VHB with experience in highway safety and roadway design. He has a B.S. in civil engineering from Pennsylvania State University.