Fairfield residents may have noticed during the past couple weeks that they?ve had to drive over black tubes on some city streets.
Those tubes belong to the Iowa Department of Transportation and are used to count traffic. Mark Hansen, transportation planner with the Iowa D.O.T., explained that they are pneumatic tubes capable of distinguishing between cars and semis based on how often the tube is pressed as the vehicle?s wheels roll on it.
Hansen said the D.O.T. wants to know traffic counts for major thoroughfares that connect to state highways, but it doesn?t just collect data on those roads. It has collected information on roads such as Burlington Avenue, B Street and Broadway Avenue. The information taken from city and county roads is then handed over to their respective governing bodies.
?We want to know, ?How can this road run more smoothly? Should we put in a traffic light? Can we justify the expense of making it three lanes or four lanes??? Hansen said. ?We want to know if there have been a lot of accidents on a particular road, and if so, find out why. Maybe a tree or a building is blocking motorists? view.?
Traffic data is particularly useful in determining whether to install a left-turning lane, or add a left-turning arrow to a stoplight like Fairfield did a few years ago at the intersection of West Burlington Avenue and 14th Street.
Hansen said the D.O.T. obtains speed data from one quarter of the state each year, and this year was southeast Iowa?s turn. The state doesn?t gather data on literally all roads, he said, but it does try to get data on the busiest roads and on roads it hasn?t sampled from in many years.
In addition to collecting data from pneumatic tubes on the ground, the D.O.T. also employs staff to sit at an intersection and count the traffic. Hansen said that some intersections are so busy that two staffers are required to count all the vehicles, whether they?re cars or semis, and which direction they turn.