Decision Modeling and the Department of Transportation

I recently received a traffic ticket on my university’s campus for driving 35mph in a 20mph zone. The street on which this violation occurred is about 2 miles long. There is a single speed limit sign regulating the zone for the direction of travel I was taking. The sign is placed on the back-side of a blind curve (a hill blocks the view of the sign). The sign is on the left side of the roadway and on the downward slope of a hill that starts just after the curve is negotiated. In addition there are perpendicular parking spaces all along the right side of the road. The last speed limit sign prior to the 20mph sign at this location is a 35mph sign on the adjacent roadway. The 20 mph sign is also located approximately 1 mile into the two mile long road.

I realize that my opinion is probable biased concerning this matter, but it didn’t seem fair to me when I was issued the ticket. I traveled the roadway the next two days looking for a speed sing but couldn’t find one that is until the third day when I walked the entire two miles of the street. I started researching street sign placement regulations on the internet shortly there after. I was able to locate the “Manual on Uniform Traffic Control Devices for Streets and Highways” (2003 edition), U.S. Department of Transportation, Federal Highway Administration. The manual can be found at: http://mutcd.fhwa.dot.gov/sitemap.htm

The remarkable thing that I found during my research was how much of the material in my Decision Support Systems class and text was used in the design of streets and highway signage and the rules associated with their placement. One additional critical factor was also involved in the process of designing the system, and that was the time factor. Signage needs to be identified, understood and reacted upon. In this case, the manual states that the entire process takes about 6 seconds or as the manual refers to the statistic as “the six second rule”.

The rules regulating street sign placement directly compare with the decision support rules concerning user presentation. First of all, street signs should appear on the right side of the road. Similar to an individual always looking in the upper right hand corner of their window application for the minimize button. If a sign is placed on the left side of the roadway, then it is “out of place” and will take longer for a user to identify. This is why I never found the sign until I walked the street. A second rule concerning signage is that the bottom of the sign must be at least 7 feet above the pavement. In the case of the sign on this street it was only 5 feet. The reason for this is so that oncoming traffic or pedestrian traffic does not block the line of sight to the sign. As the sign was placed on the backside of a hill, this further exasperated the situation. An oncoming car of pedestrian on the sidewalk in front of the sign completely obscured its view. This would be similar to having a popup window cover the control features on a screen or a warning popup being called up behind another screen.

The last item that I found in researching this issue is that speed limit signs shall be located at the points of change from one speed limit to another. In a decision support system the sign placement in this situation would be akin to having a warning window activate after you have closed the application for which the warning was issued. In all, the placement of the only speed limit sign on this road left much to be desired. In fact, there isn’t just about anywhere else on the roadway where it could have been worse.

I intend to fight this ticket, not just because I feel that the speed limit sign was improperly placed as established by the “Manual on Uniform Traffic Control Devices for Streets and Highways.” No, I intend to fight this ticket because of the basic violations of the entire streets signage design as it compares to good decision support systems design. All hail Information Systems.

Whew – I’m glade I got that off my chest. Happy motoring.