Transit-Oriented Development (TOD) Calculation

Transit-Oriented Development (TOD) Calculation involves determining the appropriate density, land use, and infrastructure needed to ensure that development around transit stations is efficient, sustainable, and aligned with TOD goals. This includes calculating the amount of space allocated for different uses (e.g., residential, commercial, and mixed-use), ensuring walkability, and integrating public transit infrastructure to reduce car dependency.

Below are some common aspects and calculations associated with TOD:

1. Density Calculation

One of the key features of TOD is higher density around transit stations. Density is typically measured in terms of residential units per acre (du/acre) or floor area ratio (FAR), and it is used to determine the extent of development that can be supported near transit stations.

  • Residential Density:
    • The number of residential units allowed per acre depends on local zoning and TOD guidelines. Higher density is encouraged near transit stations to maximize accessibility and minimize reliance on cars.
    • Example: A TOD area may allow 50 residential units per acre in a district that is within a half-mile radius of a transit station.
  • Floor Area Ratio (FAR):
    • FAR is a measure of the total building floor area divided by the lot area. TOD zones typically allow a higher FAR near transit stations to accommodate more commercial, office, and residential development in a compact space.
    • Example: A TOD zone with an FAR of 2.0 means that a building on a 10,000 square foot lot could have a total of 20,000 square feet of floor area.

    FAR Formula:

    FAR=Total Building Floor AreaLot Area\text{FAR} = \frac{\text{Total Building Floor Area}}{\text{Lot Area}}If the FAR for a specific TOD area is 3.0, and the site is 50,000 square feet, the maximum allowable floor area would be:

    Maximum Floor Area=3.0×50,000=150,000 sq. ft.\text{Maximum Floor Area} = 3.0 \times 50,000 = 150,000 \, \text{sq. ft.}

2. Transit-Oriented Development Area Calculation (Walkability)

TOD is designed to be walkable and pedestrian-friendly. To calculate walkability, the standard measure is the distance from the transit station. Generally, a 1/4 to 1/2 mile radius around a transit station is considered ideal for TOD, as most people can walk that distance comfortably within 5-10 minutes.

  • Distance Calculation:
    • 1/4 mile = approximately 1,320 feet (about 5-7 minutes of walking)
    • 1/2 mile = approximately 2,640 feet (about 10-12 minutes of walking)

3. Parking Calculation

TOD areas generally aim to reduce the need for parking spaces due to the proximity to public transportation. Local zoning rules for TOD areas often lower the required parking spaces for new developments compared to traditional suburban zoning.

  • Parking Ratio Calculation:
    • Typically, the parking ratio in a TOD area may range from 0.5 to 1.5 spaces per unit depending on the type of development (e.g., residential, commercial).
    • For example, a new residential development with 100 units in a TOD zone with a 1.0 parking space per unit requirement would need 100 parking spaces. In a more car-reduced TOD, the ratio might be reduced to 0.75 spaces per unit, resulting in 75 spaces for 100 units.

    Parking Space Formula:

    Total Parking Spaces=Number of Units×Parking Ratio\text{Total Parking Spaces} = \text{Number of Units} \times \text{Parking Ratio}For a 200-unit TOD development with a parking ratio of 0.75:

    Parking Spaces=200×0.75=150 spaces\text{Parking Spaces} = 200 \times 0.75 = 150 \, \text{spaces}

4. Transit Ridership and Infrastructure Capacity

One of the key elements in TOD is ensuring that the local transit infrastructure can handle the increase in ridership that the development will generate. The calculation of transit ridership typically involves estimating the number of people who will use public transportation from the TOD area.

  • Ridership Estimation:
    • The expected ridership is usually calculated based on density and transit accessibility. A higher density of residential and commercial uses close to transit will likely increase ridership.
    • For example, you might estimate that for every 1,000 square feet of commercial space, 15 people will use public transit, and for every 100 residential units, 120 people will use the transit system.

    Formula for Ridership Estimation:

    Estimated Ridership=(Commercial Space in sq. ft.×Ridership per sq. ft.)+(Residential Units×Ridership per unit)\text{Estimated Ridership} = (\text{Commercial Space in sq. ft.} \times \text{Ridership per sq. ft.}) + (\text{Residential Units} \times \text{Ridership per unit})Example:

    • Commercial space: 50,000 sq. ft. of office space, with an estimated 0.015 riders per square foot. Commercial Ridership=50,000×0.015=750 people\text{Commercial Ridership} = 50,000 \times 0.015 = 750 \, \text{people}
    • Residential space: 200 units, with an estimated 1.2 riders per unit. Residential Ridership=200×1.2=240 people\text{Residential Ridership} = 200 \times 1.2 = 240 \, \text{people}
    • Total Ridership: 750+240=990 people750 + 240 = 990 \, \text{people}

    The local transit authority would need to ensure that the transit station and its connecting routes can handle at least 990 additional riders.

5. Affordable Housing Calculation

TOD often includes provisions for affordable housing, which requires calculating the percentage of new residential units that should be reserved for lower-income households.

  • Affordable Housing Formula:
    • Typically, cities may require that a percentage (e.g., 10%-20%) of new residential units be set aside for affordable housing.
    • For example, if a TOD project has 500 residential units and the requirement is 15% affordable housing, the calculation would be:

    Affordable Units=500×0.15=75 affordable units\text{Affordable Units} = 500 \times 0.15 = 75 \, \text{affordable units}

6. Environmental and Sustainability Calculations

TOD policies also emphasize sustainable building practices and green infrastructure. Calculations related to sustainability could include:

  • Energy Efficiency: Estimating the energy savings from reduced car use and the implementation of energy-efficient buildings.
  • Carbon Emissions: Calculating the reduction in greenhouse gas emissions from increased public transit use, compared to a scenario where more car usage would occur.

Summary of TOD Calculations:

  1. Density Calculation: Use FAR or units per acre to estimate the level of development.
  2. Walkability: Ensure that development is within walking distance (1/4 to 1/2 mile) of transit.
  3. Parking: Estimate parking needs based on the number of residential or commercial units, adjusted for TOD policies that reduce parking requirements.
  4. Ridership: Calculate the increase in public transit ridership based on the density of the development.
  5. Affordable Housing: Calculate the number of affordable units required in the development.
  6. Sustainability: Estimate energy efficiency and carbon savings due to TOD features.

TOD calculation involves a combination of planning principles, local zoning, and transit infrastructure capabilities to ensure that the development is efficient, sustainable, and integrated with public transportation systems.