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Federal Highway Administration Research and Technology
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|Publication Number: Date: November/December 2003|
Issue No: Vol. 67 No. 3
Date: November/December 2003
Fatality rates on South Carolina's interstates were rising, but the transportation agency made dramatic improvements that save lives.
South Carolina, faced with a disturbing increase in traffic fatalities, decided to take strong action. But limited resources posed a possible hindrance to meaningful results. The challenge was daunting.
Ready to accept the challenge, the South Carolina Department of Transportation (SCDOT) and the South Carolina Division of the Federal Highway Administration (FHWA) expanded their partnership. “We decided to put our heads together and make safety our number one priority,” says FHWA's South Carolina Division Administrator Bob Lee.
Since 1992, the State's fatalities had been rising 4 percent per year. In addition, the State has the Nation's fourth largest State-maintained highway system. In the face of a rising fatality rate and budget constraints, how would South Carolina be able to improve safety?
|Based on a study of crash records and the conditions that caused median crossovers, SCDOT decided to install barriers on medians that are less than 18 meters (60 feet) wide. Photo: South Carolina DOT.|
“Because we couldn't fix everything at once, we took a focused approach,” says SCDOT Executive Director Elizabeth Mabry, “and decided to tackle the 1,336 kilometers (830 miles) of interstates as a prime target for fatality reduction.”
“Fatalities [on those highways] increased from 89 in 1997 to 162 in 2000,” Lee adds, “and because interstates are eligible for Federal aid, we knew we could allocate the funds for some measures that would bring down the fatality rate as quickly as possible.”
Mabry and Lee agreed that decreasing speed limits on the interstates where they enter urban areas would be the place to start as a low-cost, high-yield measure. Accordingly, SCDOT reduced urban speed limits in high-crash areas to 89 or 97 kph (55 or 60 mph)—a reduction of 8-16 kilometers per hour (5-10 miles per hour). SCDOT posted new signs and coordinated with the South Carolina Department of Public Safety and local law enforcement agencies.
“We knew it would be an unpopular decision,” says SCDOT Executive Director Mabry, “but our public awareness efforts minimized complaints.” The transportation agency also launched a massive public safety campaign that included nearly 7,000 “Highways or Dieways” broadcast commercials. In addition, the agency established a Web site (www.scdot.org) that ultimately received more than 2,000 hits each month.
The results speak for themselves. Since December 2000, urban interstate fatalities in South Carolina have dropped 54 percent as a result of the project.
Testing Truck Lane Restrictions
Other segments of the Interstate System still seemed to induce crashes, especially those involving commercial vehicles. In particular, Interstate 85, a major north-south route for heavy trucks, continued to have a number of crashes. National studies showed that lane restrictions potentially could lower the crash rate. When it became known that the State was considering such restrictions, the trucking industry expressed some concerns about safety and operations.
To allay industry concerns, FHWA and SCDOT implemented a pilot project to study lane restrictions. SCDOT established the restrictions temporarily for 1 year on two high-crash interstate segments. The South Carolina Department of Public Safety used targeted enforcement, both for lane violations and aggressive driving violations. The results of the lane restrictions were a 78 percent reduction in truck-related crashes. The outcome enabled FHWA, SCDOT, the SC Department of Public Safety, and the South Carolina Truckers Association to reach a consensus that restricting trucks to the two right travel lanes on three-lane sections would offer improvements in safety and traffic operations. Truck lane restrictions were expanded to 170 kilometers (106 miles) of interstates in the State.
Since the full implementation of truck lane restrictions in 2001, truck crashes on interstates in South Carolina have increased slightly, but fatalities involving heavy trucks have decreased.
Increased lane densities, increased speeds, and unprotected narrow median strips can combine to produce a far higher potential for head-on crashes.
The Message Is in The Median
Narrow, unprotected median sections were under the scrutiny of the two partner agencies. Median crossover crashes on interstates in South Carolina warranted special attention because of the devastating effects and multiple loss of lives almost always associated with this kind of incident. In 1999-2000, more than 70 people in South Carolina lost their lives in 57 separate interstate median crashes. Causes for median crossovers include inattention, fatigue, improper lane changes, medical emergencies, and equipment failure, among others.
Were these median crossover crashes occurring at a particular location or set of locations? To find the answer would require the analysis of some 3-5 years' worth of crash reports, numbering between 24,000 and 40,000. A cursory review of some of the fatality data indicated that these incidents were random in nature and did not appear to be isolated to specific locations.
A series of three median crossover crashes that killed 13 people in a 3-month period on one 16-kilometer (10-mile) stretch of highway raised doubts about this theory. The three incidents suggested that the narrower the median strip and the higher the traffic volumes, the greater the chances for a head-on collision. In addition, the length of the on- and off-ramps in this section, short by today's standards, appeared to contribute to frequent vehicle weaving conflicts. SCDOT and FHWA established priorities for correcting these dangerous situations, and determined top candidates for installation of barrier systems based on median widths of 11 meters (36 feet) or less. All traffic barrier systems used on the National Highway System must conform to the National Cooperative Highway Research Program (NCHRP) standard for crash barriers—NCHRP-350 criteria (NCHRP's Recommended Procedures for the Safety Performance Evaluation of Highway Features, NR-350). Although five types of crashworthy barrier systems are available (see “Barrier Systems Compliant with NCHRP-350 Criteria”), each has its advantages and disadvantages, and some would not be entirely satisfactory for South Carolina interstates.
The three-strand cable system was deemed most appropriate for installation as it is the safest for motorists, has the lowest initial cost, and can be installed in medians at least 7.3 meters (24 feet) wide and on 6:1 slopes (0.3 meter of incline for every 1.8 linear meters or 1 foot of incline for every 6 linear feet). The chief drawback is that the three-strand cable system requires a high level of maintenance. Each time it is struck, it collapses, making it necessary to rebuild after every crash. SCDOT estimated the project could cost $40 million.
|To prevent distracting other drivers, crash vehicles like this one are removed from the scene of the incident as rapidly as possible-usually within 1 hour but often in less time.|
In August 2000, Executive Director Mabry and Division Administrator Lee concluded that the study period was over, and it was time to act. They agreed to redirect construction funds and undertake a 5-year plan at $8 million per year, using 100 percent Federal-aid funds to install the cable barrier system on all prioritized medians. Because of the urgency of the program, the State Transportation Infrastructure Bank and other sources subsequently made additional funds available. Mabry accelerated the cable median barrier program, and the first contract was awarded in October 2000.
Through leadership and the dedication of additional resources, the contracts were completed on January 31, 2003, with the installation of 506 kilometers (314.5 miles) of three-strand median cable at a considerably reduced cost of $18.5 million on all interstate segments with medians less than 18 meters (60 feet) wide. In other words, the 5-year program was finished in about 2 years and significantly under budget.
As the program progressed, it became evident that the number of median incursions was far higher than was anticipated originally. The system was averaging more than three “hits” per mile per year. Through July 2003, the system sustained more than 3,000 hits. But more surprising than the number of hits was the number of “saves.” Only 15 vehicles—less than 1 percent of those that hit the median barrier—penetrated the cable system, resulting in 8 median crossover fatalities.
To ensure that damaged cable was repaired rapidly and returned to service, the contracts stipulated that the contractor restore the damaged section completely within 96 hours of notification. A statewide contract now provides for maintenance of the cable system to ensure continued effectiveness. Repair costs now average approximately $1,000 per hit.
|Repair crews are on the scene 48 hours or less after a median incursion is reported. Repairing the barrier usually takes 1 hour or less and requires no lane closings during the repair. Here a crew is using a portable pole driver to install a new pole.|
Significantly, most of the penetrations involved vehicles operating outside the restraining capabilities of the specifications in NCHRP-350, involving high speeds or hitting the barrier at angles greater than 25 degrees. Heavy trucks exceeding the system's stopping capabilities also accounted for penetrations.
Early in the program, rural emergency service providers and local law enforcement agencies expressed concerns about their need for U-turns across the median in some rural areas. The transportation partnership assembled an inclusive team to evaluate the need and make a recommendation. The team concluded that median openings should be provided for emergency turnarounds at 8-kilometer (5-mile) intervals, according to AASHTO guidelines. The openings have improved surfaces, but motorists are deterred from crossings by flexible barriers.
Barrier Systems Compliant with NCHRP-350 Criteria
This system is considered the safest for motorists and also has the lowest initial installation cost. It can be installed with a single run near the center line of the median and can be used on slopes with a 6:1 ratio. It requires the highest level of maintenance.
This is the standard steel guardrail that requires a dual run for narrow median protection. It also must be installed on slopes 10:1 or flatter.
This is a tubular system that also requires a dual run for narrow median protection and a slope no steeper than 10:1.
Modified Three Beam
This steel guardrail requires a dual run for narrow median protection and a slope no steeper than 10:1.
Concrete Safety Shape
This is the most rigid of the median barrier systems and also the most costly, as it requires extensive grading, drainage, and paving. It also requires a slope no steeper than 10:1, but it is the system that requires the least maintenance.
Of Repairs and RUSH
One other area that received the partnership's attention was the interstate on- and off-ramps, many of which were now unsafe by today's standards and traffic volumes because of their lengths or locations. “At $20 million to $30 million to reconstruct just one typical interchange,” Lee says, “we would never be able to catch up and improve safety and operations systemwide.”
The partnership identified some 20 interchanges for low-cost safety improvements totaling $10 million, and the program was given a name, Ramp Upgrades for Safer Highways, or RUSH for short. The transportation agency launched the program with a pilot project and evaluated the results before initiating the full-fledged program. Most of the projects were completed in 2002, and new projects are under development.
|Fatal Crashes Caused by Crossing over Interstate Medians|
|Source: South Carolina DOT
The chart shows that fatal crashes were rising before SCDOT instituted its multifaceted program to improve safety. Following installation of the cable barrier system, the number of fatal crashes dropped dramatically.
Doing More with Less
“Being in the five top States in highway fatalities for over a decade is not an envious place to be,” says Lee. “Through thoughtful planning, partnering, public awareness, and a focus on results, SCDOT and FHWA have curbed the increase in fatalities in South Carolina since 1999, in spite of very limited resources,” Mabry says. “We are pleased to have reduced interstate fatalities 36 percent in just 2 years.”
Lee adds, “Each of the initiatives discussed here met some opposition. Motorists don't appreciate reduced speed limits, truckers don't want lane restrictions, and local law enforcement and emergency responders questioned the loss of total access to interstate medians. Not one of these initiatives would have moved forward but for the leadership and genuine commitment to improving highway safety exemplified by Elizabeth Mabry, executive director at SCDOT and my partner.”
Ron Zeitz is a senior editorial consultant in FHWA's Public Affairs office in Washington, DC. His career spans more than 30 years in public relations, much of it in the private sector, working for high-tech companies. He is the former editor of The FHWA News, FHWA's publication for its employees and retirees.