GreenTRIP Connect Glossary of Terms


Affordable units: Housing designed for low-income households, so residents do not spend more than 30% of their income on rent. Prices are subsidized below market-rate (BMR). See Below Market Rate.

AMI: Area Median Income (AMI) is the middle-point of a county's income distribution. Half of the population will have incomes above this value, and the other half will have incomes below. Each year AMI is updated by HUD (The US Dept. of Housing and Urban Development) for each county, and the income qualifications for affordable housing are based on AMI, considering the size of the household.

Bikeshare: A service that gives members 24/7 access to a fleet of unattended bicycles on a short-term basis. These bicycles can be accessed at one station, and returned to a different station, if only one-way travel is needed. Reservations are not necessary, as a key-fob will access any available bicycles. Example services include Bay Area Bike Share and Citi Bike. See examples of actual housing developments within a ¼ mile of bike share pods in the GreenTRIP Parking Database.

Block size: Average size of all blocks that intersect within a 1/2 mile buffer from the selected parcel(s). A measure of an area's walkability - smaller blocks mean greater walkability. 

BMR: Below Market Rate units are homes subsidized to be affordable to low-income residents. Most subsidies require that the units are to be affordable and are deed-restricted for the life of the project, or 55 years. There are several levels of affordability: Moderate-Income, Low-Income, Very Low-Income and Extremely Low-Income. All are defined relative to the county AMI each year, and depending on the size of the household.

Carshare: A service that gives members 24/7 access to a fleet of unattended vehicles on an hourly basis. Members reserve a car online or via mobile app to access the car. Example services include ZipCar and Getaround. See our carshare info sheet to learn more about car sharing programs in the San Francisco Bay Area. You can also see examples of actual housing developments providing car sharing service on site in the GreenTRIP Parking Database.

Cost of parking: Our costs do not explicitly include the cost of land but do reflect a relatively higher cost compared to the baseline costs cited in the national VTPI report. We have verified with developers participating in the GreenTRIP Parking Database study that these costs are in the ballpark of what today’s Bay Area developers are paying in 2014. Todd Litman, VTPI (and GreenTRIP Advisory Committee member) puts surface parking at $10,000/space, garage at $20-40,000/space (p. 5.4 - 17). We don’t currently have a cost for bike parking. Litman estimates it at 5% of a car parking space (p. 5.4 - 22). The table below shows the values we used to calculate the cost of parking construction:

Type of Parking Spaces Cost
Surface Spaces (outside uncovered, or with canopy, but not enclosed, on-site and off-street) $20,000
Garage Structured Spaces (enclosed within a common garage at street level or above) $50,000
Underground Spaces (below street level, including partially underground) $80,000

Default values: Connect automatically populates the number of housing units, based on the county in which the parcel is located. The low impact parking estimate auto-fill number is also impacted by the rents and unit-size mix.

Depth of affordability: A measurement of housing affordability, based on the income ranges of residents. These ranges are defined as a percentage of the AMI. For example, "Extremely Low-Income" units are designated for residents earning less than 30% of AMI, while "Moderate Income" units are for residents earning 80-120% of the AMI.

Employment density: Number of jobs per half-mile in a given location.

GHG emissions: Greenhouse Gas (GHG) emissions are climate change-inducing gases released into the atmosphere. These gases most commonly originate as a byproduct of fuel combustion, a result of automobile travel. Examples include CO2 and methane. By reducing GHG emissions, housing developments are helping mitigate climate change.

GreenTRIP Strategies: Characteristics of a development that reduce car traffic among residents: affordable units, unbundled parking, transit passes, carshare, and bikeshare.

High Quality Transit Area: High Quality Transit Areas (HQTAs) are areas where rail or bus lines arrive at least every 15 minutes, and offer service seven days per week. These areas offer ample transportation choices beyond owning a car.

Lifts (parking): Automated machinery that moves cars into stacked arrangements, increasing the number of cars that can be stored in a given area. Using a key, residents "call" their car when needed, and the machine brings the car to ground level.

Low Impact Parking Estimate: The total number of parking spaces estimated based on your building's location and total units. This is also affected by the average rent and unit size included in building. See Methodology

Median commute distance: The middle-value of the distribution of commute distances, measured in miles, at a given location.

Municipal parking requirement: Connect defaults this value to 2.2 recognizing that some cities are still requiring 2 spaces/unit with guest parking at .2 spaces per unit. If your location has parking requirements that differ from this, you can enter that ratio here. The "dollars saved on parking construction" value will change to show a comparison with the municipal parking requirement.

Parcel: Piece of land that has an owner or owner(s).

Parking maintenance: Maintaining parking is an operating cost that needs to be considered when building parking spaces to serve a residential development project. Parking maintenance costs are presented with default costs, but can be customized by the user. Maintenance costs are estimated at $500/space annually. Source: Victoria Transport Policy Institute, 2016

Resident parking: Parking spaces exclusively for residents, rather than for guests.

Resident transit passes: An unlimited-use transit pass, typically paid for a year at a time, often with funds provided by developers to partially or completely cover the cost. See our transit pass info sheet to learn more about transit pass programs in the San Francisco Bay Area. You can also see examples of actual housing developments providing free or discounted transit passes to residents in the GreenTRIP Parking Database

Size of a parking space: To calculate the space saved from building parking below the municipal requirement (in the project report), we use the industry standard of 300 square feet per parking space. This includes drive aisles and space for maneuvering. Standard parking space dimensions are 9 feet by 19 feet. This can be more or less depending on the city or type of space (such as compact, oversized, disabled). Source: Victoria Transport Policy Institute, 2016

Surface parking: Above-ground parking spaces that are not enclosed in a garage or other structure.

Tandem parking: Two or more parking spaces arranged one behind the other, so that the farthest space can only be accessed by passing through the nearest spaces. Tandem spaces are a means of maximizing the number of cars that can be stored in a given area, but can require some management for optimal use.

Unbundled parking: Charging for parking separate from rent is “unbundling.” By unbundling parking spaces, the developer helps residents to recognize the true cost of car ownership, and make an informed decision about whether to own a car or not. Households without a car are not required to pay for parking they do not use. The monthly charge is a price signal. See examples of actual housing developments with unbundled parking in the GreenTRIP Parking Database

Units: A unit is a living space that is occupied as separate from other residents of the building (i.e. an apartment). The GreenTRIP Connect model only considers units within multifamily developments.

VMT: Vehicle miles traveled (VMT) is the measure of distance traveled by a single vehicle over a given period of time. Connect expresses expected driving per household by daily or annual VMT.

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