Monday, September 19, 2011

How do we know where the lane lines go?

To be honest, I’ve never really wondered how our striping crews and contractors know where to paint the lines on our roads. I guess I just never thought about how it happened. It’s actually an interesting question, though, when you stop to think about it. I mean, when we repave a road and cover up the old lines, how does the striper know where to put the new lines again? How do they keep them so straight?

I probably would have never thought of the question either. It just wasn’t on my radar. But that’s the nice thing about my job; I get asked some great questions. This time Laurel, who reads my Whatcom County email updates, asked the question. So I had to do the research to figure it out.

Here’s what she asked: While driving northbound I-5 (south of Bellingham) during the recent repaving, I found myself wondering how on earth they get the stripes in the right place on the road. It can't just be that the person operating the striping truck is a steady driver, and I can't imagine a GPS system would be precise enough. What's the secret technology?

Answer: Before we begin the repaving, we reference where the center line is by placing markers off to the side of the road. We put markers down at the beginning and end of every curve and about every 500 feet along the road. Once the markers are in place, there are a variety of ways we can repaint the lane lines again. Often, we’ll use a typical tape measure and spray-paint marks for the shoulder and center lines, using the markers (along the side of the road) as measuring points. Then, we may use a string line or survey instrument to put spray-paint marks on the road at 50-foot intervals. The marks are often referred to as a “tattle-tail” and help the striper know where the final lane line goes. The striping truck is quite computerized and even has a video camera on board. The driver keeps the camera pointed at the tattle-tail line to help keep the final lane line relatively straight.

And that’s how it’s done – no secrets involved.

2 comments:

Anonymous said...

We used to call them "cat tracks", as they were made by using a rope approximating the straight or curve, and then manually daubing the rope with a paint brush, leaving a double mark.

Johnny Devious said...

Also called "Layout". Old lines are measured from survey points and a line pulled between them. Spray paint is applied over the line and the painter on the back of the paint truck uses his own steering wheel to move the paint guns to follow the "ghost" left by the line and the spray paint.

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