Comparative studies usually require a classification system as a means of comparing the various subjects. For example, geomorphologists sometimes classify streams by “order” as a means of comparing differing watersheds. The stream order typically relates to the number and nature of the stream tributaries. Likewise, a sociologist may organize countries by economic gross domestic product as a means of comparing the nutrition or life expectancy of different regions.
Similarly, a study of roadside garbage requires a classification system in order to make useful comparisons about the garbage found along different kinds of streets. An effective system applies to a wide range of circumstances, deals with the complex nature of the study subjects, and provides a useful comparison. For a roadside garbage comparison, the amount and type of traffic are useful criteria, because the amount and type of garbage are likely strongly correlated to the amount of traffic along a road. By comparing streets of similar traffic patterns, insights can be gained regarding the origin of the garbage.
One way to unify and describe both traffic volume and traffic type is throughness; that is, the likelihood that someone will turn onto another street before reaching their destination. On through streets, someone is much more likely to turn on onto a connecting street before reaching a destination. Short street segments are much less likely to see through traffic, and a lower traffic volume should be expected. The traffic type is also affected by throughness. Less-through streets are more likely to have traffic that has a connection to the local neighborhood (they live or work there), and that may influence roadside garbage. One may be less likely to litter on a street near their house.
Complicating the situation is the anastamosing nature of street systems. Streets start and stop, curve, change from small to large, and can vary in type of traffic in a very short distance. Any system of describing streets needs to account for this variability. A method that classifies streets segments by their uninterrupted length, and number and nature of their intersections is described below.
First-order streets. The major streets in a community are first-order streets. These streets span multiple neighborhoods and are used primarily as a means of traversing the city. First-order streets must travel at least one mile, and have at least two intersections with other first-order streets. Any stop signs along a first-order street must also stop traffic in the opposing direction.
Second-order streets: These streets have at least two intersections, one of which is a first-order street. Second order streets are “one turn” from a first-order street, sometimes used as shortcuts, and access large neighborhoods or business areas. The main difference between first order and second order streets is uninterrupted length.
Third-order streets: These streets have at least two intersections, but do not intersect a first-order street. Someone would need to make at least two turns from a first-order street in order to reach a third-order street. Because of their out-of the way nature, most traffic is assumed local, especially vehicular traffic. A small number of pedestrians and bicyclists may use these streets as short cuts.
Fourth-order streets: These streets have only one intersection with another street. The intersecting street may be of any other order. Fourth order streets are dead-end streets and all traffic on these streets is assumed local.
This classification system is simple enough to make comparisons about roadside garbage, yet exceptions and ambiguity undoubtedly occur. Using this system, the 36th street segment would be a first-order street, and the Fairmont segment a second-order street. I am curious to see how the garbage along these streets compares to that of 3rd or 4th order streets, or other 1st or 2nd order streets in different neighborhoods.