U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
This presentation is intended for State and local safety engineers and professionals. The information presented here provides more information on intersection safety and the tools needed to develop and implement an Intersection Safety Implementation Plan (ISIP), regardless if your agency has an existing ISIP or is just interested in improving intersection safety.
Data for Intersection Focus Area from FHWA Safety Data Dashboard at: rspcb.safety.fhwa.dot.gov/Dashboard/Default.aspx
The Federal Highway Administration (FHWA) has identified three focus areas as providing the greatest potential to reduce highway fatalities using infrastructure improvements–intersections, roadway departure, and pedestrian/bicyclists–because they account for about 90 percent of all fatalities. In 2014, intersection crashes resulted in 8,664 fatalities.
There are three approaches agencies can use to improving intersection safety. The hot-spot is a more traditional approach but is expensive and only addresses issues as they arise. The systemic approach addresses all locations, regardless of crash data. This requires less analysis but more funding. The comprehensive approach identifies locations with the greatest risks, rather than exact locations. Analysis can focus on crash types or facility types and similar characteristics. This allots the funding to priority intersections.
Policy and culture also influence safety improvements, although on a much broader perspective and higher level.
Traditional Approach: cost-effective but minimal impact
The FHWA Systemic Safety Project Tool presents step-by-step guidance on conducting a systemic safety analysis process for incorporating systemic safety planning into traditional safety management processes. The Systemic Tool provides a step-by-step process for conducting systemic safety analysis; considerations for determining a reasonable distribution between the implementation of hot-spot safety improvements and systemic safety improvements; and, a mechanism for quantifying the benefits of safety improvements implemented through a systemic approach. State and local transportation safety practitioners can use this tool to plan, implement, and evaluate systemic safety improvement programs and projects.
The systemic safety planning process consists of four steps that can be adapted based on the availability, quality, and quantity of data and technical resources. Similar to other common safety management processes, the steps include identifying the problem, screening and prioritizing candidate locations, selecting countermeasures, and prioritizing projects. It begins with analyzing and identifying focus crash types – those representing the greatest number of severe crashes – and potential risk factors. Then, the process moves to a micro-level assessment of locations across the network. This leads to selecting appropriate countermeasure and then prioritizing projects. This is an iterative process; and, as shown by the upwards arrows, some steps may be revisited for adjustments throughout the process.
FHWA has developed a guide to developing an ISIP. The Intersection Safety Implementation Plan Process provides more detail on the 10-step process for developing an ISIP. To set a crash reduction goal, States should consult their Strategic Highway Safety Plan.
Example: Reduce fatalities by a total number, by a given date
Example: Reduce fatality rate for each year of the last 5 years of data
SHSP goals tend to take two forms: crash frequency and crash rate.
ISIPs are meant to lead agencies to think systemically.
Signalized and Stop-Controlled Intersections
Type of intersection control provides a natural classification of countermeasures, whether (1) specific to signalized intersections, (2) specific to stop-controlled intersections, or (3) applicable to either type.
The data analysis will follow this general process.
Separate Intersection Crashes into Sub-Groups
Determine Target Crash Types
Calculate Average Crash Costs and Severities
Determine Distribution of Crash Densities
Prepare Data Analysis Package
|State rural signalized||Local rural signalized|
|State urban signalized||Local urban signalized|
|State rural stop-controlled||Local rural stop-controlled|
|State urban stop-controlled||Local urban stop-controlled|
Classifying intersection crashes according to maintaining agency, area type, and control type can yield the following sub-groups.
|STATE||Area Type||Total # of Crashes||Fatal||A||B||C||PDO||Unknown|
Here is an example of such data from one State. Note that, depending on the sources and quality of the data, there may need to be some "unknown" categories.
…Don't let the perfect stand in the way of the good!
No agency's system is perfect, but sound conclusion can be drawn and decisions made based on the information that is available.
Establish Threshold Crash Levels
Develop Detailed Tables for Each Countermeasure
Compile a Summary Outline
The "straw man outline" refers to the high-level benefit-cost analysis that should be coordinated for the intersection countermeasure considered. Crash thresholds can be used to influence the numbers of instructions targeted based upon the anticipated funding and much of the ISIP. Construction and maintenance costs are compared to the expected monetary benefits from crashes prevented in the B/C analysis.
Look for opportunities to integrate the ISIP with other statewide programs and funding streams:
A typical signing detail for stop-controlled T-intersections. This image was included in a slide presentation that the ODOT central office provided to the districts.
Engage local agencies, MPOs/RPOs, and other stakeholders to enhance:
States with ISIPs: Washington, Oregon, Arizona, Texas, Oklahoma, Louisiana, Missouri, Mississippi, Florida, Georgian, South Carolina, North Carolina, Tennessee, Indiana, Ohio, Pennsylvania, Maryland, New York, New Hampshire, Massachusetts
By formally adopting the ISIP, States were able to garner buy-in from decision makers, integrate the plan with other plans (SHSP), and develop policy changes. On the other hand, other States found that a draft ISIP is more flexible and can change when new data or funding becomes available.
Partial systemic: Treating locations with low to moderate crash histories, with a focus on widespread deployment of only low cost packages of improvements
Corridor systemic: Consistent treatment of multiple intersections along an extended distance of roadway with the low-cost treatment packages. Multiple intersections identified as low to moderate crash histories along a defined corridor
This is the most difficult of the three, as many States face barriers associated with data.
This is the most difficult of the three, as many States face barriers associated with data. Full Systemic: Treating intersections entirely on risk characteristics identified through rigorous safety data analysis. This is the most difficult of the three, as many States face barriers associated with data.
Advance Signal Ahead warning sign with cross street name. Source: SCDOT.
Signage upgrades that include doubling up the intersection warning signs, adding cross street names, and yellow flags above the signs. Source: PennDOT.
After implementing several systemic countermeasures across the State, Florida has consistently met their goal of 5% reduction in fatalities and injuries. However, it is hard to determine if this decrease is a direct result of the systemic approach or other contributing factors.
To date this has all been done though a Rural Safety Innovation Program grant received from FHWA. LADOTD received $4.1 million of RSIP funds. $2.0 million was awarded for rural intersection treatments and $2.1 million was awarded for roadway departure treatments. Only locations in the Delta Parishes were eligible for these funds. LADOTD let to construction their first 104 intersections which included 88 rural stop controlled intersections and 16 rural signalized intersections. Construction was completed in December 2010.
The bids on the initial project came in under estimate, so LADOTD was able to let to construction an additional 100 intersections in September 2010. They also supplemented the leftover RSIP funds with regular safety funds for this project. LADOTD were able to do 90 rural stop controlled intersections and ten rural signalized intersections. The average cost per intersection was $10,000.
Instead of doing a statewide project for its next round of improvements, LADOTD decided to limit their project to individual districts. In Louisiana, there are nine DOTD districts that will let nine separate projects. LADOTD also decided to take a corridor approach and address both intersections that are in the action plan and curves that they identified as needing low-cost countermeasures.
Rural 4-leg Stop:
53% reduction All Crashes
64% reduction Severe Crashes
Rural 3-leg Stop:
67% reduction All Crashes
56% reduction Severe Crashes
Louisiana evaluation can be found at safety.fhwa.dot.gov/local_rural/delta/
This is a before shot of an intersection where LADOTD implemented LADOTD improvements. Note that staff had previously doubled up on the advanced warning signs.
The experience in South Carolina has been the subject of an ongoing evaluation by 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 433 stop-controlled intersections. Results for the signalized intersection treatments show a 10.7-percent reduction in fatal and injury crashes and an 11.7-percent reduction in right-angle crashes, both at a 95-percent confidence level. A 4.5-percent reduction of total crashes at the 90-percent confidence level was found as well. Results for the stop-controlled intersection treatments show an 8.3-percent reduction in total crashes, a 10.7-percent reduction in fatal and injury crashes, 6.7-percent reduction in rear-end crashes, 5.9-percent reduction in right-angle crashes, and 14.7-percent reduction in nighttime crashes. All results for stop-controlled are statistically significant at the 95-percent confidence level with small standards of error.
Jeffrey Shaw, P.E.
FHWA Office of Safety