Improving Safety through South Carolina’s 

Intersection Safety Implementation Plan (ISIP) 

Introduction 

In 2007, the South Carolina Department of Transportation (SCDOT) released its Strategic Highway Safety 

Plan1(SHSP) and included intersections as an emphasis area. To assist South Carolina with its efforts on the 

intersection emphasis area, the Federal Highway Administration (FHWA) provided technical assistance to 

SCDOT in the spring of 2008 that included the development of its Intersection Safety Implementation Plan 

(ISIP). FHWA held a workshop, provided a data package, and identified a list of candidate intersections by 

countermeasure type in the summer of 2008. The latest SHSP (published in March 2015) continues the 

commitment to improve intersection safety, once again including intersections as an emphasis area. 

Process and Results 

After the completion of the 2007 SHSP, engineering improvements to highway safety targeting high-crash 

intersections and roadway corridors produced positive results. SCDOT implemented a number of 

intersection improvements in the State consisting of low-cost safety treatments, such as signing, pavement 

markings, LED signal indications, and backplates with retroreflective borders on traffic signal heads. SCDOT 

also used higher-cost countermeasures—such as realignments, turn lanes, and roundabouts—at high-crash 

intersections. The early success with the low-cost safety treatments provided the State with confidence to go 

forward with a wide-scale implementation. 

Since then, SCDOT has completed three 

statewide contracts to improve signs and

pavement markings and deploy signal 

enhancements at approximately 2,200 

intersections as of December 2014. The 

improvements are consistent with those 

identified in the ISIP. In an effort to accelerate 

the project and reduce costs, the State 

eliminated several construction items that added 

time and cost to complete. Therefore, any 

improvements requiring more substantial 

construction, such as pedestrian ramps at 

intersections and splitter islands, were not 

included in this contract. More information on 

this project is available at South Carolina Case

Study: Systematic Intersection Improvements. 

1 SCDOT. 2015. Strategic Highway Safety Plan. https://www.scdot.org/performance/pdf/reports/Target-Zero-Strategic-HwySafetyPlan-2015-18.pdf. South Carolina Department of Transportation, Columbia, South Carolina.

Advance Signal Ahead warning sign with cross street name. 

Source: SCDOT.
FHWA-SA-16-083 

Revised June 2020

In addition, J-turn configurations (in which vehicles are prohibited from turning left from the minor-road 

approach and instead must turn right and make a downstream U-turn) are also being implemented statewide 

at divided-road intersections. There are currently 10 such projects that are either complete or under design. 

South Carolina has adopted new standards and policies 

for all intersection projects based on ISIP-related 

implementation. This includes the installation of more 

roundabouts for intersection control, which has led to 

approximately 15 completed roundabouts and an 

additional 20 still under design or construction. 

SCDOT has also standardized backplates with 

retroreflective borders and LED signal indications for 

all new or modernized traffic signals. 

To implement all countermeasure packages at all 

locations outlined in the ISIP represents an investment 

of approximately $30 million beyond currently-programmed intersection safety projects over a five-year 

period—or $6 million annually. Over the last three-year period, from 2012 to 2014, SCDOT allocated nearly 

40 percent of its Highway Safety Improvement Program funding to address safety issues at intersections with 

improvements such as roundabouts, left-turn lanes, and other geometric and traffic control improvements. 

Expected Outcome 

As part of the FHWA Evaluation of Low-Cost Safety Improvements Pooled Fund Study, an evaluation is 

currently being conducted to develop crash modification factors (CMFs) for the countermeasure packages 

implemented at both stop-controlled and signalized intersections. The CMFs will serve to compute an

expected number of crashes after implementing a given countermeasure at a specific site2. The preliminary 

findings of the evaluations indicate the enhancements at stop-controlled intersections are expected to have an 

8-percent reduction in total crashes and a 15-percent reduction in nighttime crashes. The enhancements at

signalized intersections are expected to have an 11-percent reduction in fatal plus injury crashes and a 12-

percent decrease in angle crashes.

Contact 

Daniel Hinton

Safety and Operations Engineer 

Federal Highway Administration - South Carolina 

Division 

803.253.3887

daniel.hinton@dot.gov

2

 FHWA. CMF Clearinghouse. U.S. Department of Transportation. Federal Highway Administration. 

http://www.cmfclearinghouse.org/. 

Joey Riddle

Safety Program Engineer 

South Carolina Department of Transportation 

803.737.3582

riddlejd@scdot.org

Reflectorized backplates during the day (left) and at 

night (right). Source: SCDOT.