State engineers have long maintained that median cables are an effective and low-cost way of doing that. So why didn't the state install them all the way along the brand new portion of the 540 extension, the new toll road in the Triangle?
The ABC11 I-Team put that question to state traffic engineer Kevin Lacy. He told us it's not about money or critics who've questioned the effectiveness of cable barriers verses solid ones. Lacy said it's actually because on some parts of 540, the median is so wide that barriers wouldn't be effective.
"It's that balance between can a vehicle recover and go about their normal business or will it cross the median - and 70 feet was that distance - in North Carolina, where we found we got that diminishing return," Lacy explained.
In the Tar Heel state, 70 feet is the magic number where engineers have decided drivers are better off without the cable barriers.
Lacy said 93 percent of car crashes that end in someone dying happen on roads with a median narrower than 70 feet across.
"Are we saying that there's no chance of a vehicle crossing the median above 70? No. We've had 'em cross over 100 feet. But it's such a rare event," he explained.
It all boils to a numbers game and trading off the possibility of a serious crash with the likelihood of property damage if there were the medians cables.
But there are roads, like the I-40 extension, where there are medians about 70 feet wide and median cables were installed.
Lacy said that's because there have been recorded accidents in those areas where vehicles have crossed the median.
Lacy told us the 70-foot guideline appears to be working. The number of fatal cross-median crashes around the state have gone from about 40-50 a year to just 10.
He said if the unprotected stretches of 540 prove dangerous, the DOT will reconsider.