More Fun with the DOT

July 13, 2005

I asked Nura to determine the locations and lengths of the legs on the Type 1 signs on our project. These Type 1 signs are the big green signs that you see on the interstate that indicate ramps ahead or whatever. The calculation of these legs are seemingly an easy task to do. I printed out the standard detail drawings for the installation. Ideally the edge of the sign should be 30 feet from the edge of the travel lane. In the plan it lists the size of the sign and the recommended distance between the legs. For sign number 1, the size is 22 X 11, (the width of the sign (L) is 22 feet) and the distance between legs (S) was given as 13.2 feet. On the plan which I printed out it gives the simple formula for calculating the offsets for the legs. For those in the cheap seats the legs should be at (30 + (L-S)/2) and (30+ (L-S)/2+S). So real quick that would be 34.4 and 47.6. I told Nura before we went out to locate the signs that she should calculate the locations and also set up a spreadsheet to make things easier because we also had to shoot elevations at these locations. And if you set things up ahead of time especially in a neat format like in a spreadsheet, life will be good. So Nura says that she has everything calculated. We go out to the first sign and she has leg offset numbers of 45.4 and 58.6. We mark out these locations and I say, “These look way off. Let’s go for a drive.” I had never calculated the offsets for these type of signs before either. I have always found that if you have a question about how something is done. Find a place where this task has been done and copy it. Also the same philosophy I used to get through Linear Systems Analysis in college. We drive out to Highway 16, an established and well traveled road for years, and start measuring the distance from the edge of travel lane to the first leg. We get to one that is around 34 feet to the leg and 30 feet to the edge of the sign. Nura says to me “That seems about right, because it is 30 feet to the edge of the sign.” Now mind you at this point, I have assumed that Nura is an engineer who should be able to do come simple adding, subtracting and division, so I did not check any of her work. So I do some quick math in my head and say to Nura, “Do you mean to tell me that the sign hangs 15.4 feet from the first leg of the sign?” Nura replies to me, “You know what, I think I made a mistake.” On the drive back to the project, Nura asked me if I thought she had no common sense at all. I said no, of course not.