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Designing a traffic monitoring program using landuse change detection
Iowa DOT's procedure
The state of Iowa has approximately 130 permanent count locations spread across the state for traffic data collection and a manual count schedule to satisfy the federal mandates.  Figure 1: Map of Iowa showing the four counting zones and the level of data collection The state is divided into four zones as shown in figure 1. Each year a quarter of the state is selected for collection of traffic counts. The counties, which are hatched, are chosen in a cycle for complete counts, which includes the secondary roads and the counts for only the primary roads are collected in the remaining counties in the zone. Thus, for primary (principal) roads, a data collection cycle is completed once every four years (one quarter of the state is counted every year). Secondary (non-principal) roads are counted only every eight years. Growth and changes in landuse as well as infrastructure development affect traffic patterns, and clearly, some areas grow more than others. To respond to this, and to make the procedure more efficient and provide the timeliest data, the present process allows out-of turn counting. The determination of change and prioritization is based on recommendations from state, county, and city officials. However, this procedure is highly subjective and only "significant" changes in landuse and network are considered. The studies performed every year are conducted using mechanical and manual traffic counts. The mechanical counts are performed using portable automatic traffic controllers and are setup for a period of 24 to 48 hours. The manual counts are input directly into a microprocessor and are usually conducted in two time periods of four hours each or three consecutive eight hour slabs. "The traffic monitoring program of Iowa Department of Transportation is approved by the FHWA and satisfies or exceeds the TMG recommendations regarding sample size and stratification to calculate traffic within 10% with 95% confidence."[3] Changes at the Iowa DOT As described in the previous section, all the roads in the state were being monitored for determining the traffic patterns, at least once every eight-years. Prior to 2000, Iowa law mandated a Quadrennial Needs Study (QNS) that required the Iowa DOT to conduct extensive field inventory of the state's 110,000 miles of road. During this survey process, DOT field personnel could easily observe locations of development and land use change. This information formed an important part of the data needed to locate an efficient count program. The 2002 legislative session resulted in the termination of the QNS, in favor of a regional fund allocation process. This eliminated the need for DOT field survey of local roads, and has resulted in the need for a new method to direct efficient counting of traffic. |