Indian River County Impact Fee Study Final Report - irccdd.com

Residential Functional Population
It is generally assumed that people spend one-half to two-thirds of their time at home and
the rest of each 24-hour day away from their place of residence. In developing the
residential component of IRC functional population for fees using a 24-hour versus 11-
hour approach, an analysis of IRC population and employment characteristics was
conducted. Based on this analysis, it was estimated that, in the case of 24-hour days,
people, on average, spend 15.6 hours, or 65 percent, of each 24-hour day at their place of
residence and the other 35 percent away from home. In the case of 11-hour days, people
spend 3.8 hours, or 35 percent of their time, at their place of residence and the remaining
65 percent away from home. This analysis is presented in Appendix A, Tables A-9
through A-11, and resulting percentages are displayed in Tables II-9 and II-10.
Nonresidential Functional Population
Developing estimates of functional residents for nonresidential land uses is more
complicated than developing estimates of functional residents for residential land uses,
given the varying characteristics of non-residential land uses. Nelson and Nicholas
originally introduced a method for estimating functional resident population, now used
internationally. 1 This method uses trip generation data from the Institute of
Transportation Engineers' (ITE) Trip Generation Manual, information on passengers per
vehicle, workers per vehicle, length of time spent at the land use, and other variables.
Specific calculations include:
• Total one-way trips per employee (ITE trips times 50 percent to avoid double
counting entering and exiting trips as two trips).
• Visitors per impact unit based on occupants per vehicle (trips times occupants per
vehicle minus employees).
• Worker hours per week per impact unit (such as nine worker hours per day times
five days in a work week).
• Visitor hours per week per impact unit (visitors times number of hours per day
times relevant days in week such as five for offices and seven for retail shopping).
• Functional population coefficients per employee developed by considering time
spent by employees and visitors at each land use.
Table II-9 shows the functional population coefficients for nonresidential uses/categories
in IRC for the year 2004 based on a 24 hours per day, 7 days per week analysis.
1 Arthur C. Nelson and James C. Nicholas, "Estimating Functional Population for Facility Planning,"
Journal of Urban Planning and Development 118(2): 45-58 (1992).
Tindale-Oliver & Associates, Inc.
Indian River County
May 2005 II-8 Impact Fee Study