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:
- field explicit_chunk: float = 0#
If > 0, use this chunk size instead of adaptive chunking. If less than 1, use this fraction of the total number of rows.
- field land_use_columns: list[str] = []#
Only include the these columns in the computational tables.
This setting joins land use columns to the accessibility destinations.
Memory usage is reduced by only listing the minimum columns needed by the SPEC, and nothing extra.
- field land_use_columns_orig: list[str] = []#
Join these land use columns to the origin zones.
This setting joins land use columns to the accessibility origins. To disambiguate from the destination land use columns, the names of the columns added will be prepended with ‘landuse_orig_’.
Memory usage is reduced by only listing the minimum columns needed by the SPEC, and nothing extra.
Added in version 1.3.
Examples#
Implementation#
- activitysim.abm.models.accessibility.compute_accessibility(state: State, land_use: DataFrame, accessibility: DataFrame, network_los: Network_LOS, model_settings: AccessibilitySettings | None = 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.