Click for next page ( 48

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement

Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 47
47 Table 2.12. Best-fitting multiple regression equation increasing the density of potential development, lowering the for predicting PM peak trip generation rates as a capital cost for parking, enhancing the financial viability of proportion of ITE rate for TOD housing projects. TODs, and increasing transit ridership. AM Peak Rate Building TOD Case Studies Std. Coeff. Err. t Statistic Prob. As an input to this part of the research, TOD master plan- Distance to CBD (in miles) 0.013 0.005 2.631 .021 ners from PB PlaceMaking were asked to prepare alternative site plans for an eight-acre residential TOD. Parking ratios Residential Density: Dwelling Units per Gross Acre within mile of were varied between the alternatives: one reflected conven- station -0.026 0.009 -2.893 .013 tional ratios in many existing TODs and one tested tighter Household Size: Persons per ratios more consistent with the results of this research. The Dwelling Unit within mile of station -0.190 0.107 -1.772 .100 site plans were prepared for four different representative TOD Constant 0.964 0.264 3.657 .003 residential development products (garden apartments, town- homes, a Texas Donut and mid-rise housing) for a total of eight Summary Statistics: different site plans. (A Texas Donut refers to a parking struc- F statistics (prob.) = 7.491 (.004) R Square = .634 ture surrounded by usable residential space. In an article in Number of Cases = 17 Places, Brian O'Looney and Neal Payton describe Texas Donuts as unadorned parking decks bordered on two sides by a 10-15 foot zone for open ventilation, and wrapped on all four 0.9 1 unit/acre sides by 35-40 foot deep four-story wood-frame liner residen- 0.8 tial buildings ( PM Rate as prop. of ITE Rate 0.7 5 units/acre cgi?article=1998&context=ced/places). The development types 0.6 10 units/acre tested were selected because they are indicative of the resi- 0.5 dential development products found in a number of U.S. 15 units/acre 0.4 TODs. The potential development types reflect the range of 0.3 20 units/acre built products included in the field research for this study. The site plans ranged in density from 24 to 120 units per 0.2 acre. 0.1 Since there are no clear national standards for parking 0 TODs, a quick survey of parking ratios in adopted station area 0 5 10 15 20 25 plans was conducted. The review revealed a considerable Distance to CBD (miles) range of latitude in how TODs are parked. For the case stud- Figure 2.18. Influences of residential densities and ies, parking ratios were selected from two TOD zoning ordi- distance to CBD on transit-oriented housing PM trip nances for station areas on the Washington Metrorail: one in rate as a proportion of the ITE rate. Maryland and one in Virginia. The TOD 1 ratio of 1.1 park- ing spaces per unit (one space per unit and one visitor space two transit-oriented apartments 10 miles from the CBD, if for every 10 units) is consistent with how Arlington County, the surrounding residential densities are 10 units per acre, Virginia parks high density TOD in the Rosslyn-Ballston the PM trip rate will be 45% of the ITE manual's rate. If the Corridor on the Orange Line (U.S. EPA, 2006). The TOD 2 surrounding densities are 20 units per acre, the PM trip rate ratio is 2.2 parking spaces per unit (two spaces per unit and one will be just 20% of the ITE rate (or 80% lower). visitor space for every five units) and is consistent with how Prince Georges County, Maryland parks high density TOD for the West Hyattsville TOD on the Green Line (Prince Georges Applying the Research: Four TOD County, 2006). Housing Case Studies For an apples to apples comparison, the underlying as- This section looks at some of the physical implications of sumptions were held constant for each potential development varying residential parking by analyzing four TOD case stud- product, even though in a real word example they would be ies designed with two different parking ratios. Using four dif- expected to vary somewhat to respond to unique site condi- ferent representative TOD residential development products, tions. In each case study the unit size was assumed to be 910 the analysis provides a glimpse at how changing parking within square feet net or 1200 square feet gross. This provides for a a TOD can have an impact, such as improving physical form, mix of unit sizes (1, 2, and 3 bedroom units) within the project.

OCR for page 47
48 Parking is assumed to consume 300 square feet per space residential TOD products analyzed in the case studies. Those allowing for aisles and landscaping. While parking ratios vary differences include: considerably across the United States, these ratios provide a means to help isolate the impacts of parking ratios on urban A 20% to 33% increase in the number of potential units in form. The parking ratios tested in the site plans were 2.2 spaces a TOD. As might be expected, a lower parking ratio results per unit and 1.1 spaces per unit. in less land being used for parking which can be used for development. In the four case studies, potential additional residential units from lower parking ratios ranged from an Learning from the Case Studies increase between 20% to 33%. Representative site plans (Figures 2.192.22) help illustrate The case studies show how the two ratios result in sig- some potential implications for TOD housing of how adjust- nificantly different density on a site. The most pronounced ing parking ratios reflect the actual transportation perfor- percentage increase in potential units was seen with the mance of TODs in form, density, and performance. Varying lower density garden apartment and townhome examples parking ratios and holding other factors constant suggest a because all the parking is surface spaces. Reducing parking number of important differences in what could be constructed from 2.2 to 1.1 spaces per unit resulted in the ability to in- on the eight-acre theoretical TOD. Table 2.13 provides a crease the potential number of units on the site by 33% for summary of some of the quantifiable differences in density, both garden apartments and townhomes. The greatest cost, and ridership from varying parking ratios for the potential absolute increase in the number of units was achieved by 2.2 Parking spaces per unit 1.1 Parking spaces per unit Total Area: 8 acres Total Area: 8 acres Total Units: 196 Total Units: 256 Additional units: 60 Density: 24 Dwelling units per acre Density: 32 Dwelling units per acre Increase in density: 33% Parking Spaces: 432 Parking Spaces: 288 Parking capital cost: $2.1m Parking capital cost: $2.02m Parking cost savings: $98,000 Annual incremental ridership: +19,500 Annual incremental fare revenue: $19,750 Figure 2.19. Comparison of representative TOD housing: garden apartments.

OCR for page 47
49 2.2 Parking spaces per unit 1.1 Parking spaces per unit Total Area: 8 acres Total Area: 8 acres Total Units: 288 Total Units: 384 Additional units: 96 Density: 36 Dwelling units per acre Density: 48 Dwelling units per acre Increase in density: 33% Parking Spaces: 648 Parking Spaces: 448 Parking capital cost: $6.56m Parking capital cost: $5.82m Parking cost savings: $736,000 Annual incremental ridership: +31,200 Annual incremental fare revenue: $31,600 Figure 2.20. Comparison of representative TOD housing: townhomes. lowering the parking ratios for the higher density products, fabric of a community the cost of a special feature like a re- the Texas Donut and the mid-rise building. tail wrap or an enhanced faade typically pushes the cost of Lower total construction costs for parking even with more a space to around $28,000 to $32,000. residential units. Parking in any form is expensive to build. As the site plan studies help demonstrate, tighter park- Reducing the amount of parking required in a TOD by ing ratios can be a key driver in the capital cost of TODs. rightsizing parking as suggested by the results of this re- The cost savings were most pronounced with the higher search can be important to the economic viability of a density development prototypes (mid-rise and Texas TOD. To help understand the cost implications of parking, Donut) where structured parking is employed. In these ex- a review of 2007 parking costs was completed (G. Stewart, amples the savings in reducing parking ranged from 25% to e-mail message, December 2007). The review shows just 36%. For the lower density examples the parking savings how expensive parking can be. Surface parking spaces can was in the order of between 5% and 11% depending on the cost from $5,000 per space for low-end asphalt to $10,000 development product. with details like cobbles and brick pavers. Parking tucked The real significance of the parking capital cost numbers under a townhome can cost about $14,000 a space. In indicated in the case studies is to understand the numbers dense conventional multi-family development such as the are not simply an apples-to-apples comparison of reduc- Texas Donut or mid-rise buildings open undecorated ing the parking by half. As the case study shows, a reduction parking decks cost anywhere from $17 - $20,000 per space. in parking results in an increase in the number of potential If the parking deck is to be incorporated into the urban units on the site (which need to be parked) by 20% to 33%

OCR for page 47
50 2.2 Parking spaces per unit 1.1 Parking spaces per unit Total Area: 8 acres Total Area: 8 acres Total Units: 801 Total Units: 963 Additional units: 162 Density: 100 Dwelling units per acre Density: 120 Dwelling units per acre Increase in density: 20% Parking Spaces: 1800 Parking Spaces: 1152 Parking capital cost: $33.3m Parking capital cost: $21.31m Parking cost savings: $12m Annual incremental ridership: +52,650 Annual incremental fare revenue: $53,330 Figure 2.21. Comparison of representative TOD housing: mid-rise 6-story. (see Table 2.14). With the mid-rise case study, for exam- units .40 TOD work mode share + 4 nonwork trips per ple, an additional 162 units could be built and still result in TOD HH TOD units .10 TOD nonwork mode share a developer saving approximately $12 million in the cost of (Lund et al., 2004) = daily ridership 325 annualization parking. In this instance reducing the parking ratio by 50% factor = the annual incremental increase in ridership attrib- resulted in a capital cost savings of 25% for parking while utable to changes in parking ratios. Because the mode share also increasing the number of residential units by 20%. factors are specifically for TODs, no additional adjustments Higher transit ridership. Increasing the potential number of for changes in density or automobile ownership were made.] residential units in a TOD also can be expected to increase As one might expect the incremental ridership benefit in- transit ridership. The actual increase in ridership can be creases proportionally to the number of additional units. expected to vary considerably depending on local conditions. The additional annual transit ridership which might be Drawing on the body of existing research summarized in the attributable from the potential units made possible by low- literature review, it is possible to make some crude prelimi- ering parking ratios is summarized in Table 2.15. nary assessments of the ridership implications of increasing Parking and financial feasibility of TODs. Apart from the im- the potential density in a TOD. [Transit ridership was esti- pacts on the physical form of a TOD the shear amount and mated consistently for each of the case studies: drawing on cost of parking can be a driver in the financial viability of a the field research, 3.55 trips were assumed for each TOD proposed TOD and in turn the financial return to a household. Transit ridership: 3.55 trips per TOD household developer. As discussed earlier, lowering parking ratios can allocated as follows: 1.5 work trips per TOD HH TOD affect the financial viability of a TOD in a number of ways. In