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22 Table 24. Transit share at work sites with alternative land use characteristics. Percent Trips By Transit Principal Land Use Conditions With Land Use Without Land Use Characteristic1 Characteristic Characteristic Offices, residential, retail, personal services, Substantial land use 6.4% 2.9% parks within mile of site mix Four or more services, service frequency, Accessibility to 6.3% 3.4% sidewalks, transit, transit stops services Restaurant, bank, child care, dry cleaner, Availability of 7.1% 3.4% drug store, post office convenience services Sidewalks, street lighting, pedestrian Perception of safety 5.4% 3.6% activity, no vacant lots Trees, shrubs in sidewalk zone, wide sidewalks, small building setbacks, no Aesthetic setting 8.3% 4.2% graffiti 1 Sites also have TDM programs. mode results were reported for a pair of neighborhoods in justification varied. A national survey in 1994 indicated that northern California (38, p. 15-79). 17% of responding agencies that required TISs permitted re- Transit mode shares at work sites vary based on different ductions for mixed use (42). Permitted reductions reported land use characteristics. As Table 24 shows, transit ridership averaged 10%. is higher--approximately double--with substantial land Procedures vary significantly--for example, Destin, Florida, use and services mixes than without (38, p. 15-86). Providing states that any claim for internal capture rate must be justified safety and aesthetics also produce greater willingness to use by the applicant based on empirical data for similar land uses transit. located in similar urban environments. Data are to be from a Table 25 shows some bottom line elasticities contained in source generally acceptable to the transportation planning TCRP Report 95, Chapter 15 (38, p. 15-117). Local density, profession. Any internal capture rate exceeding 25% must be diversity, and design all have modest impacts on both vehicle justified and approved by the city (43). The City of Tempe, trips and VMT. A Portland, Oregon, METRO report found a Arizona, simply requires that capture rates and sources of source that concluded that residents of mixed-use, gridded information be documented and limits internal capture to no neighborhoods in the San Francisco area made 15% fewer au- more than 15% (44). The City of San Diego uses a simple tomobile trips and 22% more walking trips than did residents method. It stipulates internal capture reductions to be used, of typical suburban neighborhoods (40). It is not clear if other providing a table of reductions by land use type (i.e., residen- factors were kept constant. tial, industrial, office, or retail) by time of day (i.e., daily, A.M. peak, and P.M. peak) (45). Table 26 is a reproduction of San Current Practice Diego's table. Retail reductions are permitted only if the re- tail is neighborhood oriented and more than 100,000 sq ft. All When using TIS became more widespread during the three approaches are used in a variety of cities. San Jose, Cal- 1970s and 1980s and developers took more interest in mixed- ifornia, limits internal capture to a maximum of 10%, but and multi-use development during the same period, traffic provides a bonus if there is a commitment to travel demand study preparers and reviewers began to focus on internal trip management programs and if nearby transit is available in ad- capture. In a 1993 survey of 15 Texas cities that required TIS, dition to the site being mixed use (46). In California, Caltrans 11 permitted reductions for MXDs (41). One had a set reduc- indicates that internal trip capture rates may exceed a 5% re- tion percentage and a minimum development size; the oth- duction, but requires approval and review with transporta- ers required justification, and what constituted acceptable tion staff (47). Table 27 was compiled by the research team Table 25. Typical travel elasticities related to land use density, diversity, and design. Elasticity Characteristic Description Vehicle Trips VMT Local density (residents + employees)/ land area 0.05 0.05 Local diversity (land use mix) Jobs/population balance 0.03 0.05 Sidewalk completeness, route directness, Local design 0.05 0.03 street network density

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23 Table 26. Permitted internal trip capture reductions, City of San Diego. Percent weekday internal trip reductions for MXDs that include Land use within predominantly neighborhood-oriented commercial retail MXD A.M. Peak Hour P.M. Peak Hour Daily Residential 8% 10% 10% Industrial 5% 5% 4% Commercial 5% 4% 3% Office Commercial * * * Retail * Commercial retail reduction equals the sum of the total mixed-use reduction in residential, industrial, and commercial office. Source: (45) and lists a total of 21 agencies and their requirements for an indicator of mixed land uses); street network and sidewalk accounting for internal capture for MXDs. densities; distance to transit; and travel times. The methodol- For the U.S. Environmental Protection Agency, Criterion ogy is calibrated and applied at the traffic-analysis-zone level. Partners developed geographic information systems (GIS) It uses zone-level regional travel model trip generation as a based software, INDEX. The INDEX software assists in deter- base and applies elasticities associated with the factors listed mining the impact of a variety of community design charac- above. It does not directly use specific land use trip generation teristics on vehicle trip generation and VMT (48). As inputs to rates or equations of the type typically used in TISs. vehicle trips and VMT, the procedure uses population and ITE's Trip Generation Handbook includes a detailed method employment density; population and employment balance (as for estimating internal trip capture (1, Ch. 7). It is based on Table 27. Internal trip capture rates for selected agencies. Internal Trip Capture Procedure Justify/ ITE Trip agency State Agency Max or Agency Generation Verify with Formula approval Other flat % approval Handbook survey or table for higher procedure rate AZ Phoenix (1015%) Tempe (15%) Tucson CA Caltrans (5%) L.A. County Newport (10%) Beach Pasadena San Diego San Jose (10%) TDM bonus CO Boulder FL Destin (25%) Additional FDOT considerations Gainesville Orlando GA GRTA (modified) IN Indianapolis Prescribed by NM NMDOT city Other approved TX Austin sources Or citywide Plano study WA Seattle Documented D.C. Washington alternative Source: Texas Transportation Institute.

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24 complementary land use by number of development units, development because the rates developed by ITE were based trip generation rates, and trip capture percentages for any on suburban vehicle-oriented travel patterns and may be given pair of land use classifications for which data are avail- lower than the same land uses in high-density MXDs (14, able and provides a balancing computation to ensure the ori- p. 7-3). gin and destination land uses can send and receive the same URBEMIS2002, a national model for calculating air-quality number of internal trips. It assumes convenient internal impacts of projects, contains adjustments to reflect the effects connectivity. It depends on empirical data supplied from of several land use and design factors discussed earlier in this surveys; data in the handbook are from studies transmitted chapter. Internal trip capture-related factors specifically in- to ITE. cluded in formulas that compose the adjustment factors are as The Georgia Regional Transportation Authority (GRTA) follows (51, 52): requirements represent a more specific approach now more commonly used (49): it requires use of the ITErecommended Net residential density (households per net acre; excludes practice as documented in ITE's Trip Generation Handbook land consumed by arterial right-of-way); (1). However, GRTA modifies the procedure in accordance Mix of land uses (based on number of study area [0.5 mile with a table that reduces the adjustments according to a com- radius] households and employment--a jobs/housing bination of distance between complementary uses and whether balance--with a 2% bonus for inclusion of retail within the bicycle/pedestrian facilities are provided (see Table 28). Any study area); other claims for internal trip reductions must be approved by Transit service index (function of buses stopping within GRTA in advance. 1 /4 mile of site, number of rail or bus rapid stops within A survey conducted in 2004 by ITE indicated that 64% of the 1 /2 mile of site, number of dedicated daily shuttle trips); respondents use the method provided in the Trip Generation Pedestrian/bike score (function of intersection density, Handbook (50). The responses were from a combination of and sidewalk and bike lane completeness); and preparers and reviewers, so the percentages should not be in- Parking supply (function of parking provided/ITE parking terpreted as representing the portion of agencies that require a generation rate). given method. Multiple responses were permitted, so the total does not add to 100%. A total of 12% reported they use locally Formulas are provided for each of the reductions, but the established methods; 34% reported they use rule of thumb documentation does not provide complete explanations of (usually specific percentage) methods; and 19% reported they how the formulas were derived, and it appears that at least one use other detailed methods. The locally established and other formula (reflecting residential density) is based on assump- methods include engineering judgment, specific considera- tions that are not supported. Nevertheless, URBEMIS2002 tions, state DOTs or other guidance, distance-based method, provides for air-quality emissions estimation trip reductions ULI shared parking rates, results from surveys, and travel fore- of up to the amounts shown in Table 29. The numerical in- cast model. Land uses for which internal capture estimates are formation was developed using a variety of sources including desired were most frequently reported to include retail, resi- some referenced above. Further review of additional support- dential, office, hotel, health club, theater, and conference cen- ing documentation would be needed before the formulas ter, but several other uses were also mentioned. Those that col- should be considered for use in this project's improved estima- lected new data usually have done so mainly through interview tion method. The reports' text states that redundancy has been surveys, although several other methods were reported includ- removed by using reduction factors within the equations. ing traffic and turning movement counts, parking durations/ Ewing slightly deviated from the standard classification of trips turnover, and field observations. in the modeling process when studying communities in Palm Additionally, Kittelson & Associates note that it is not advis- Beach County. Ewing treated trips as part of tours rather than able to apply internal capture rate reductions in very-high- home-based or non-home-based (53). Assessing trips as part density MXDs that generate activity that exceeds suburban of a multistop and multipurpose tour or activity-based traffic Table 28. Adjustments to ITE Trip Generation Handbook mixed-use internal trip capture rates. Percent of full reductions allowed by Bicycle/pedestrian facilities distance between complementary uses provided mile or less mile mile > mile Yes 100% 67% 33% None No 67% 33% None None Source: (49)