Between November and January, five trucks rolled over on a single highway ramp in Georgia's DeKalb County. "I'm not an engineer," says a WSB-TV traffic reporter, "but common sense says there's something wrong there." Now experts may be able to explain it. There are two key issues, says a road engineering consultant. For one thing, the curve on the ramp linking Interstate 285 southbound and Interstate 20 eastbound comes right after more than half a mile of straight highway—and drivers tend to speed up on straightaways, meaning they're in some cases going as fast as 75mph when the curve (recommended speed 35mph) comes upon them. Trees add to the problem, making it hard to spot the curve in advance. The second issue is that drivers' eyes seem to trick them, and it's something a state engineer noticed.
A lane to the right of drivers (on the other side of a low median barrier wall) keeps going straight as the ramp's lanes curve. "There's a bit of an optical illusion … where if you don't notice the curve coming, and you're looking straight ahead, it looks as if the road continues," says a rep for GDOT. It plans to take action: GDOT says it will install six truck tip-over signs and new speed warnings. As for the optical illusion, officials will shield the problematic lane from view by placing reflective panels atop the median wall. Interestingly, optical illusions have also been used to achieve the opposite effect: safer driving. These have ranged from a 3D image of a girl chasing a ball into the street, as the Globe and Mail reported in 2012, to "hash marks" spaced to trick drivers. (Read more optical illusion stories.)