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100 This step is to balance the estimates of directional internally For the bottom row in sub Tables 9-A(D) and 9-A(O), there captured trips between the interacting land uses. This must be are no internal trips (no data to support such estimates). Val- performed for two reasons: ues are taken directly from Table 103, sub Table 1-A, the right two columns. Totals from sub Tables 9-A(D) and 9-A(O) are 1. Estimates for each land use are based on the quantity of then entered in Table 103, sub Table 5-A. The entering and exit- that land use and its capacity to send or receive internal ing values in Row 1 of that table are the totals from Column 4, trips. There is no assurance without balancing that there sub Tables 9-A(O) and 9-A(D). The total in Column 2 is the is enough capacity on the receiving end to accept as many sum of the entering and exiting volumes. The second row trips as are being sent. of sub Table 5-A is the sum of Column 2 of sub Tables 9-A(O) 2. The total trips sent internally (i.e., captured trips) from one and 9-A(D) divided by the sub Table 5-A, Row 1 entries then use to another must equal the number being received at the multiplied by 100%. The remaining entries in sub Table 5-A other end of the trip. Both numbers must be the same. are taken from sub Tables 9-A(D) and 9-A(O) in a similar manner. Sub Table 6-A is computed using the row figures in Figure 20 shows this process. To perform this computa- sub Tables 9-A(D) and 9-A(O). tion, person trips begin from Table 104, sub Tables 8-A(O) Use the corresponding tables to compute P.M. street peak- and 8-A(D). Compare corresponding cells and select the lowest hour estimates. figure (i.e., the fewest unconstrained internal trips). For exam- ple, compare the "from retail to office" cell. If sub Table 8-A(O) shows 4.4 trips and sub Table 8-A(D) shows 70.4 trips, select Reminder the lower value (i.e., 4.4) and enter it into the "retail to office" The previous computational description follows a spread- cell of Table 103, sub Table 4-A in round numbers (4, in this sheet workbook designed to have a cover sheet that contains example). Complete sub Table 4-A of Table 103 in this manner. all input and output of interest, with look-up data and inter- These are the estimated internal trips. mediate computations on the subsequent worksheets. It is As shown above, P.M. street peak-hour estimates can be intended that the spreadsheet workbook be used to perform computed using the corresponding tables. computations. If performed manually, analysts may wish to reorder component tables to provide a more logical order. Step 6: Calculate the Overall Internal Capture Rate for the Site Additional Guidance In Table 104, sub Tables 9-A (D) and 9-A(O) are used to Site Location summarize internally captured trips and compute the exter- nal trips. This is started in person trips. Column 2 of sub The researchers recognize there is internal capture for Table 9-A(D) is computed by summing the office column of developments other than single, physically and functionally sub Table 4-A of Table 103. Column 4 comes directly from integrated MXDs (such as CBDs and SACs). The concept of Table 104, sub Table 7-A(D), Column 4. The external trips in unconstrained internal capture rates constrained by the mix Column 3 are the difference between the total and internal and proximity of land uses also applies to those development person trips in each row. patterns. However, the data reported herein include only The right three columns in sub Table 9-A(D) are com- developments that satisfy the "mixed-use" definition used in puted by multiplying the external vehicle trips in Column 3 this report. of that table by the applicable mode split percentage in the two right columns of sub Table 2-A of Table 103. The transit Mixed-Use Development Already in external trips are computed by multiplying the transit mode ITE Trip Generation Database split percentage (Column 3, sub Table 2-A) by the number of external person trips (sub Table 9-A(D), Column 3). Non- In a typical shopping center that is included in the ITE Trip motorized person trips are calculated similarly. For vehicle Generation report (2), the site restaurants are convenience trips, use the equation of restaurants that feed off the retail visitors (rather than serve as destination restaurants). In some MXDs, some of the restau- external trips - transit trips rants may be oriented to the convenience of internal users and - non-motorized trips not draw heavily from outside the development. These may be vehicle trips = vehicle occupancy snack shops, fast food, or other small restaurants rather than full-scale restaurants that are destination eating places. Ana- where the vehicle occupancy comes from Table 103, sub lysts may wish to consider them part of a shopping center use Table 2-A, Column 2. if the retail uses generate a large portion of the convenience

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101 restaurant business. If this is to be done, it is suggested that The six-step estimation procedure is merely a mathemat- not more than the first 5% of overall retail/restaurant square ical technique for estimating internal capture; the researchers footage be considered as convenience restaurant. This should are not trying to suggest how to adhere to specific local TIA exclude all destination and free-standing restaurants. In such requirements. a case, if greater than 5%, assume the amount above 5% to be restaurant--generate trips accordingly and keep this portion separate for determining the internal capture rates. Add the Proximity of Land Uses convenience restaurant square footage to the retail space. The ITE Trip Generation report (2) and the Trip Generation If the analyst knows (or can confidently assume) the land Handbook (1) already include several types of MXDs. Current uses and their sizes but does not know their proximities, the ITE land use classifications that already account for internal analyst must prepare at least a schematic site plan. Do not trip-making include the following: simply assume that each pair of land uses consists of build- ings adjacent to each other (e.g., within 200 ft). At the mini- Shopping center: shopping-center trip-generation rates are mum, test different proximities and observe their effects on based on retail developments that already normally include overall internal capture at the mixed-use site. restaurant, cinema, and limited other entertainment uses; If development information is not yet detailed enough to however, "if a shopping center is planned to have out-parcel permit a direct estimate of proximity distances, use the site development of a significantly different land use classifica- size and Figure 23 to estimate the average probable separa- tion or a very large percentage of overall gross leasable area, tion, then use that distance for the proximities between each the site could be considered a mixed-use development for land use pair. This will produce rough estimates of internal the purpose of estimating site trip generation" (1). capture, at least related to proximity. As the site plan evolves, Office park with retail: "A subdivision or planned unit use more specific information for proximity. development containing general office buildings and sup- The recommended approach is to separate each land use port services such as banks, restaurants and service stations into blocks, with a block being the building faces along both arranged in a park- or campus-like atmosphere should be sides of a street (see Figure 24). Locate the centroid of the considered as an office park (ITE Land Use Code 750 form entrances of a specific land use for each block and measure dis- ITE Trip Generation report)," not as an MXD (1). tances between each block of that land use and the other inter- Office building with ground floor retail or onsite cafeteria: acting land use. If there are multiple blocks, then make mea- "An office building with support retail or restaurant facili- surements between all pairs of blocks and use the weighted ties contained inside the building should be treated as a gen- average distance, using trip generation involved in each inter- eral office building (Land Use Code 710) because the trip change as the weighting factor. generation rates and equations already reflect the presence Figure 24 shows an example of a multi-block scenario. If of such support uses" (1). the dots represent the centroid of the entrances for Land Use Hotel with limited retail and restaurant space. "A hotel A in each block, and if d1 and d2 are the respective distances with an onsite restaurant and small retail falls within Land to Land Use B in Block 3, then the weighted average distance Use Code 310 and should not be treated as a MXD" (1). between Land Uses A and B is Land Use Split between Retail and Restaurant d1 ( sq ft in Block 1 of Land Use A ) + d2 The internal capture rates presented earlier in Tables 103 t in Block 2 of Land Use A ) ( sq ft through 106 treat retail and restaurant as separate land uses. ( sq ft in Blocks 1 and 2 of Land Use A ). To use these rates, it is necessary to differentiate between retail and restaurant uses at the mixed-use site. It is possible that the analyst will only know total retail (i.e., retail plus restaurant) square footage. In that situation, two different approaches are suggested for estimating internal capture: A A A 1. Assume the same retail/restaurant split found at the six 1 d1 3 sites for which data were available; and 2 d2 A A A B 2. Assume and test different retail/restaurant splits (within a reasonable range) to determine whether the retail/restaurant split changes site trip generation and internal capture significantly. Figure 24. Sample blocks including Land Uses A and B.

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102 Proximity Adjustment Factor on the adjacent (external) street system" (1, p. 100). Pass-by trip percentages are applicable only to external trips--those The proximity adjustment factors presented previously are trips that enter or exit the adjacent street system. They should based on the observed effects of changing walk distances on be applied after the external trips are estimated, not to the internal capture rates between land use pairs. These walking base vehicle-trip generation. distances were measured along available routes that did not require the use of stairways or other obstacles or delaying fac- tors. The paths were also along clear, adequately wide walk- Unconstrained Internal Capture Rates ways in very good repair. The unconstrained internal capture rates presented in Tables 99 through 102 reflect data collected at as many as six Mode Share of Internal Trips MXDs. For several of the land uses, the potential sums of internal capture rates appear to be illogical--for example, the The great majority of internal trips to a site will be either sum of 124% for internal capture for trips to office in the P.M. walked or driven onsite (many sites also accommodate bicy- peak hour (see Table 102) is impossible. However, these cle travel)--that is, few internal trips within a site will use "illogical" sums will not occur for three reasons: major public streets either on the periphery of the develop- ment or internal to the development. An exception will be First, they would require unlikely balances of interacting trips driven within a multi-block area of complementary and land uses. For example, to maximize the inbound office interacting land uses. internal capture rate during the P.M. peak hour, the retail For those MXD sites or areas where all internal trips will be space would need to be 20 times the office space and the walked, bicycled, or driven onsite (on private internal streets restaurant space would be half of the office space; a mix or through parking areas), the mode of access to the site should with so little office is essentially a shopping center. While be used to factor vehicle external trip generation for the analy- the internal capture for trips to the office from retail would sis period. The ITE trip generation rates and equations gen- be high, the opposite would not be the case. The overall erally incorporate suburban mode splits. Limited observa- internal capture rate would be modest. tions within the ITE dataset point toward about 2% of the Second, the proximity adjustment factors will reduce trips arriving by walking, bicycling, or transit. This would be the effective unconstrained internal capture rates because a reasonable assumption to apply to ITE data. The other 98% of the possibility that all office and residential uses will not arrives as either vehicle drivers or passengers. be located within 200 ft of all retail and restaurant at the After arriving on the site, internal trips that could or might mixed-use site. be driven will be limited by (1) the convenience (or lack Third, it appears to be mathematically impossible for thereof) of driving versus walking, and (2) the availability of all unconstrained maximum internal capture percent- a motor vehicle for the trip. Some MXDs may also have inter- ages to occur at the same time within a development nal shuttles. Hence, it is a reasonable assumption that the because each maximum requires a different ratio of beginning point for internal trips by personal vehicle will be development units for the pair of land uses involved. no higher than the mode of access to the site and possibly far For example, using Tables 99 through 101, for the A.M. lower if the development is walkable. peak to achieve 65% internal capture for trips from office The mode split is used at the end of the process to deter- to restaurant, restaurant would need to have 63/23 times the mine the number of external person trips being taken by square footage of the office for a balance to be achieved personal vehicle, transit, and non-motorized modes such as (the ratio of sq ft of each land use to achieve a complete bicycle or walking. The mode split can be derived from sur- balance between sending and receiving land uses neces- veys of similar land uses near the study site or from other sary to obtain the unconstrained internal capture per- estimates relevant to the study location and land uses (e.g., centage). To achieve the 28% internal capture of trips regional or localized travel data available from MPOs or other from office to retail, the square footage of office would credible sources). have to be 28/32 times the square footage of retail. The office to residential is 0% due to the value in Table 101. So, for 100,000 sq ft of retail, office would have to have 87,500 sq ft Pass-By Trips of office and about 239,700 sq ft of restaurant to reach "The application of pass-by trip reductions should be 91% internal capture. At average size of about 5,000 sq ft applicable to (mixed-use) sites. However, none of the inter- per restaurant, that would amount to 48 restaurants, a nal trips can be of a pass-by nature because they do not travel very unlikely balance--and that is only the balance results