4:02PM Nov 27, 2019
It started out as a simple question. Why do some roads have white lines on the outer edges? and some don't? Do the lines make the road safer? It turns out there's a whole field of engineering dedicated to studying what markings go on roads and why. I'm Laura Ellis. Today on curious level w FPS. Lisa Gillespie takes us out to Shelby County, Kentucky to meet with a resident who has some concerns.
Do you ever drive down the road and think to yourself, why does this road look like this? Why the yellow line? Why are the speed limit signs in that font? Roads tend to just be there. They've always been there. And we don't really think about them until... well, there's a problem. Like you're driving at night, you can't see the yellow centerline. It's been worn down by time. Or there aren't lines where you think there should be, and this affects your safety. That was the case for our question asker.
My name is Robert Miles. I am in Simpsonville. And my question to Curious Louisville was: why do some roads have the white outer lines and others don't? What determines who gets what paint?
For 14 years, he's lived on Todds Point Road in Shelby County. There are no white outer edge lines on this road. And it's caused some problems.
People go off the edge because they don't see where the edge is, especially at night. So you know, everybody loses some fence, and God forbid anybody gets hurt, but I know it happens.
I went to see him and talk about some of his concerns.
You're taking your life in your hands every time you go through that S curve, and there's really nothing to be done about that. But the white lines, I felt, would would clarify at least to you... like when I'm going through it and there's cars coming the other way, and I'm getting semi blinded, and there's the sheen of everything, I look pretty much at the yellow line to just get my bearings of where I am on making that S curve, let alone anywhere else on the road. And that's nerve-racking, because that's the closest I am... that's the side that I'm closest to that car, as opposed to paying attention to the white line, which is what I do on every other road - on the roads that have them - so that I can go over there and know that I'm away from that car, and that I'm also not going to go off the road.
Answering this question took me all the way from Shelby County to Iowa.
My name is Omar Smadi and I work at Iowa State University. And I also direct the Center for Transportation Research and Education.
And it turns out the answer is pretty simple: It's in the manual. All states follow a federal manual from the US Department of Transportation.
The installation of pavement markings, the placement pavement markings, the color of pavement markings, the dimensions of pavement markings are all spelled out.
Then every state has its own Traffic Operations Manual which goes into more detail. So in the case of Todds Point Road, otherwise known as KY-1848, there is a reason there are no white outer lines. Here's the local part of the answer.
My name is Zachary Neihof. I'm a traffic engineer here for district five in Louisville, Kentucky.
Neihof works for the state, which maintains this road-slash-highway
For road to have both center lines, so the double yellow down the middle and the edge line, it has to meet a minimum of 20 feet.
Todds Point Road, where Robert lives, is just under 20 feet wide. On roads that are narrower than 20 feet, outer edge lines can be dangerous because drivers subconsciously drift toward the middle, closer to oncoming cars.
And so statistically, head-on collisions are far more severe than roadway departures, and so if we are forcing those drivers even just mentally to hug the center line, then we could cause and head on collision.
But there are also studies showing that white edge lines make rural roads safer, according to Smadi at Iowa State, because if all you've got are yellow lines in the middle...
Drivers, by training, shy away from these sides, so you might be pushing people to the edge of the road, which is not safe.
And Smadi said, as long as the road is more than 16 feet wide, the state could make an exception. It could conduct a safety study to determine if the road needs outer lines.
So let's say they do a safety study. This is a high crash location. They find that pavement marking is a good safety countermeasure. You probably could go and put some pavement markings, because we think it's going to help
but white lines are expensive and they fade within three to five years. And states nationwide are cash strapped. So the state could do something else. Put reflective bars in, or maybe lower the speed limit. I called our question asker Robert Miles to deliver this news. [To Robert:] So do you think you'll contact the state?
Yeah, I most likely will. I mean, I'll read through all the stuff and see what's entailed. But I have, as of right this minute, no reason why I wouldn't.
He says if they don't add outer white lines, he's at least love to see the speed limit lowered. Right now. It's 55. [To Robert:] It might not be that they need white lines. It might be that people that are speeding...
Oh I guarantee you, speeding is an issue. People lose their minds on this road.
The question for this edition of curious little boy came from Robert miles.
I'm gonna start, you know, sending in questions every week. Like, Jesus, will be just go away? [laughter]
Reporting was done by Lisa Gillespie. I'm Laura Ellis and you can ask a question of your own at Curious Louisville dot org.