Random Count Site Selection Process for Statistically Valid Estimations of Local Street Vehicle Miles Traveled

The Texas Department of Transportation (TxDOT) has identified the need a more accurate estimation of vehicle miles traveled (VMT) on streets functionally classified as local. The Texas Transportation Institute (TTI) developed a procedure to randomly select traffic count sites on local streets that results in a statistically valid estimation of local street VMT. This procedure involves using grids overlaid on maps depicting the functional classifications of streets in a given area. All grid cells are assigned sequential numbers and then a relative range of random numbers is generated. The actor then locates the grid cells that correspond to the randomly selected numbers in the order in which they were generated. Each time a cell is selected that contains a local street, the actor highlights it and marks a count location on the map. This process is repeated until an appropriate number of sites have been selected. Statistical analyses have determined how many count locations are necessary in order to provide a representative sample of traffic counts in areas, depending on the population. Median values of counts identified the number of counts at which the diminishing rate of return on the investment in the counts occurs. This procedure has resulted in median traffic count volumes on local streets that more realistically represent the variety of local streets that exist. These median volumes, derived from randomly selected sites, are considerably lower than the median volumes derived from historical count locations that are not randomly selected. In addition, there are now randomly selected traffic count locations in area types of some counties where no counts were previously performed.

• Corporate Authors:

  Transportation Research Board

  500 Fifth Street, NW
  Washington, DC  United States  20001
• Authors:
  • Frawley, William E
• Conference:
  • 11th National Conference on Transportation Planning for Small and Medium-Sized Communities
  • Location: Portland OR, United States
  • Date: 2008-9-17 to 2008-9-19
• Publication Date: 2008

Language

• English

Media Info

• Media Type: CD-ROM
• Features: Figures; Photos; References; Tables;
• Pagination: 15p
• Monograph Title: Tools of the Trade: 11th National Conference on Transportation Planning for Small and Medium-Sized Communities

Subject/Index Terms

• TRT Terms: Cartographic grids; Location; Random sampling; Statistical analysis; Streets; Traffic counting; Traffic estimation; Traffic volume; Vehicle miles of travel
• Geographic Terms: Texas
• Subject Areas: Highways; Planning and Forecasting; I72: Traffic and Transport Planning;

Filing Info

• Accession Number: 01139048
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Aug 31 2009 9:24AM