Accessibility

The accessibilities model is an aggregate model that calculates multiple origin-based accessibility measures by origin zone to all destination zones.

The accessibility measure first multiplies an employment variable by a mode-specific decay function. The product reflects the difficulty of accessing the activities the farther (in terms of round-trip travel time) the jobs are from the location in question. The products to each destination zone are next summed over each origin zone, and the logarithm of the product mutes large differences. The decay function on the walk accessibility measure is steeper than automobile or transit. The minimum accessibility is zero.

Level-of-service variables from three time periods are used, specifically the AM peak period (6 am to 10 am), the midday period (10 am to 3 pm), and the PM peak period (3 pm to 7 pm).

Inputs

• Highway skims for the three periods. Each skim is expected to include a table named “TOLLTIMEDA”, which is the drive alone in-vehicle travel time for automobiles willing to pay a “value” (time-savings) toll.

• Transit skims for the three periods. Each skim is expected to include the following tables: (i) “IVT”, in-vehicle time; (ii) “IWAIT”, initial wait time; (iii) “XWAIT”, transfer wait time; (iv) “WACC”, walk access time; (v) “WAUX”, auxiliary walk time; and, (vi) “WEGR”, walk egress time.

• Zonal data with the following fields: (i) “TOTEMP”, total employment; (ii) “RETEMPN”, retail trade employment per the NAICS classification.

Outputs

• taz, travel analysis zone number

• autoPeakRetail, the accessibility by automobile during peak conditions to retail employment for this TAZ

• autoPeakTotal, the accessibility by automobile during peak conditions to all employment

• autoOffPeakRetail, the accessibility by automobile during off-peak conditions to retail employment

• autoOffPeakTotal, the accessibility by automobile during off-peak conditions to all employment

• transitPeakRetail, the accessibility by transit during peak conditions to retail employment

• transitPeakTotal, the accessibility by transit during peak conditions to all employment

• transitOffPeakRetail, the accessiblity by transit during off-peak conditions to retail employment

• transitOffPeakTotal, the accessiblity by transit during off-peak conditions to all employment

• nonMotorizedRetail, the accessibility by walking during all time periods to retail employment

• nonMotorizedTotal, the accessibility by walking during all time periods to all employment

The main interface to the accessibility model is the compute_accessibility function. This function is registered as an Inject step in the example Pipeline.

Structure

• Configuration File: accessibility.yaml

• Core Table: skims

• Result Table: accessibility

Configuration

settings activitysim.abm.models.accessibility.AccessibilitySettings

Bases: PydanticReadable

Settings for aggregate accessibility component.

Fields:

• CONSTANTS (dict[str, typing.Any])

• SPEC (str)

• land_use_columns (list[str])

• source_file_paths (list[pathlib.Path])

field CONSTANTS: dict[str, Any] = {}

field SPEC: str = 'accessibility.csv'

Filename for the accessibility specification (csv) file.

field land_use_columns: list[str] = []

Only include the these columns in the computational tables

Memory usage is reduced by only listing the minimum columns needed by the SPEC, and nothing extra.

Examples

• Prototype MTC

• Prototype ARC

Implementation

activitysim.abm.models.accessibility.compute_accessibility(state: State, land_use: DataFrame, accessibility: DataFrame, network_los: Network_LOS, model_settings: Optional[AccessibilitySettings] = None, model_settings_file_name: str = 'accessibility.yaml', trace_label: str = 'compute_accessibility', output_table_name: str = 'accessibility') → None

Compute accessibility for each zone in land use file using expressions from accessibility_spec

The actual results depend on the expressions in accessibility_spec, but this is initially intended to permit implementation of the mtc accessibility calculation as implemented by Accessibility.job

Compute measures of accessibility used by the automobile ownership model. The accessibility measure first multiplies an employment variable by a mode-specific decay function. The product reflects the difficulty of accessing the activities the farther (in terms of round-trip travel time) the jobs are from the location in question. The products to each destination zone are next summed over each origin zone, and the logarithm of the product mutes large differences. The decay function on the walk accessibility measure is steeper than automobile or transit. The minimum accessibility is zero.