Fix Child Benefit opt-outs, rental flags and bus fare modelling

changelog.d/1852.fixed.md

@@ -0,0 +1 @@
+- Keep the unimplemented Scottish Two Child Limit Payment inactive in the baseline, with explicit counterfactual tests.

changelog.d/1871.added.md

@@ -0,0 +1 @@
+- Price supplied person-level bus journeys with regional yields, single-fare caps and proportional reform controls, preserving reported spending for legacy data.

changelog.d/2064.fixed.md

@@ -0,0 +1 @@
+- Recognise housing-association tenants as renting and share the rental tenure predicate between households and benefit units.

changelog.d/2065.fixed.md

@@ -0,0 +1 @@
+- Preserve the independent Child Benefit claim gate, restore opted-out claimants' payments when a reform lowers the charge below a configurable behavioural threshold, and handle cliff charges without division warnings.

docs/engineering/bus-fares.md

@@ -0,0 +1,138 @@
+# Bus fares from journeys
+
+The model prices supplied person-level local-bus journeys from 2024 onwards.
+`person_bus_fare_spending` sums London and other-local-bus spending;
+`bus_fare_spending` sums it across household members. These outputs describe
+spending. `transport_consumption` already includes bus spending, so consumers
+must not add it to the consumption total again. This implementation does not
+change transport consumption, disposable income or government subsidy totals.
+
+## Inputs and fallback
+
+The Microcosm `nts_bus_travel` stage supplies `bus_in_london_trips`,
+`other_local_bus_trips`, their sum `local_bus_trips`, `bus_pass_eligible` and
+`local_bus_single_fare_share` at Person level. Trips are annual quantities.
+A supplied zero counts as journey data. A cached default does not. If only
+`local_bus_trips` is supplied, London residents' trips use the London series
+and other residents' trips use the other-local-bus series. When either split
+series is supplied, that split takes precedence and the absent series is zero.
+Supply consistent splits for cross-boundary travel.
+
+The model treats a person flagged `bus_pass_eligible` as travelling free,
+matching Microcosm's pricing assumption. The dataset owns that eligibility
+flag; the model does not infer concessionary eligibility from age or change
+it when a concessionary scheme is reformed. Supply `bus_pass_eligible` alongside
+journey inputs, including in household calculators; an omitted flag defaults to
+false and the person pays fares even if eligible for a statutory concession.
+For fare-paying passengers,
+`local_bus_single_fare_share` is the share of boardings bought as singles,
+bounded to [0, 1]. Its fallback is 0.70, the 2024 NTS other-local-bus estimate.
+An optional `local_bus_uncapped_single_fare` overrides the representative
+uncapped fare described below. Negative quantities and fares price at zero.
+
+On loading a UK `Simulation`, a supplied household `bus_fare_spending` moves
+to `bus_fare_spending_reported`. The stored total therefore cannot freeze the
+journey formula in a reform. Without journey inputs, the model retains this
+reported total and allocates it using `fare_allocation_weight_by_age`.
+Reported totals retain CPI uprating. Wales and unknown regions retain the
+reported total even when journey inputs exist, following Microcosm's decision
+to leave areas without published receipts unpriced. Before 2024 the model
+also uses this legacy route. Direct core/YAML tests can still override the
+household output explicitly.
+
+## Published price benchmark
+
+Microcosm prices journeys using FY2024–25 published facts. The model uses the
+same inputs. For each area, receipts `R`, boardings `B`, concessionary
+boardings `C`, annual trips per resident `T` and population `P` give:
+
+- Fare-paying yield per boarding: `y = R / (B - C)`.
+- Boardings per resident trip: `k = B / (T * P)`.
+
+| Area | R (£) | B | C | T | P | y (£) | k |
+|---|---:|---:|---:|---:|---:|---:|---:|
+| London | 1,347,434,943.01459 | 1,821,485,000 | 497,523,765.08908 | 13.1155774642333 | 58,620,101 | 1.017729905895 | 2.369144880275 |
+| England outside London | 2,069,953,713.42079 | 1,850,509,887.26131 | 519,107,608.59444 | 28.0685543170643 | 58,620,101 | 1.554716967657 | 1.124669202640 |
+| Scotland | 391,000,000 | 334,000,000 | 183,599,374.01433 | 28.0685543170643 | 5,546,900 | 2.599723222144 | 2.145240985363 |
+| Northern Ireland | 150,082,817.49 | 67,794,551.35 | 8,960,000 | 28.0685543170643 | 1,927,855 | 2.550929922065 | 1.252853758464 |
+
+Sources: [DfT BUS01 and BUS05i](https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables),
+[NTS0705a](https://www.gov.uk/government/statistical-data-sets/nts07-car-ownership-and-access),
+[Scottish Transport Statistics 2025, tables 2.2a and 2.8](https://www.transport.gov.scot/publication/scottish-transport-statistics-2025/chapter-2-bus-and-coach-travel/),
+[NI Public Transport Statistics 2024–25, figures 3, 4 and 6](https://www.infrastructure-ni.gov.uk/publications/public-transport-statistics-northern-ireland-2024-25),
+and [Microcosm's fact extraction and pricing implementation](https://github.com/PolicyEngine/microcosm/pull/954).
+Population denominators use ONS mid-2024 estimates. London uses all English
+residents because non-residents also travel there. Scotland and Northern
+Ireland use the English other-local-bus trip rate as a proxy, as Microcosm does.
+These translations include interchanges and differences between operator
+boardings and resident trips; they are not counts of legs for a known trip.
+
+## Caps and the uncapped counterfactual
+
+`gov.dft.bus.fares.cap` records the national cap on participating single-ticket
+services in England outside London: £2 from January 2023, £3 from January 2025,
+and £2 from January through December 2027. After December 2027 it is infinite,
+representing the end of the announced scheme. These dates follow the
+[DfT evaluation](https://www.gov.uk/government/publications/evaluation-of-the-2-bus-fare-cap),
+[£3 scheme guidance](https://www.gov.uk/guidance/3-national-bus-fare-cap) and
+[2027 announcement](https://www.gov.uk/government/speeches/2-bus-fares-from-january-2027).
+The cap does not affect the London series, Scottish or Northern Irish fares.
+England outside London uses a representative participating-service assumption;
+route-level participation and local lower caps require caller-supplied fares.
+
+The published yield already includes ticket discounts and the benchmark cap.
+For an English fare-paying person's other-local-bus boardings, the model uses:
+
+```
+current_yield = max(0, benchmark_yield + single_share *
+                   (annual_min(uncapped_fare, current_cap) -
+                    annual_min(uncapped_fare, reference_cap)))
+spending = trips * boardings_per_trip * current_yield
+```
+
+`annual_min` caps the fare in each date interval, then weights the intervals
+from 6 April to 5 April, assuming uniform journeys through the year. It does
+not cap a fare using the average cap. Both `fares` and `reference_fares` preserve
+calendar dates. `reference_year` is 2024 and `reference_fares` holds the benchmark
+schedule fixed when the policy cap changes. The source receipts use 1 April to
+31 March; this approximation treats them as the corresponding model year's
+benchmark. Annual Scenario changes apply to the full model fiscal year.
+
+The default uncapped fare is £2.748019953976. This is an aggregate assumption,
+not an observed fare distribution. The FY2024–25 cap grant is £515,693,216.60.
+With `F = B - C` outside London and single share `s = 0.70`, the assumption
+solves `s * (u - annual_min(u, reference_cap)) = grant / F`. Since `2 < u < 3`,
+the reference year has 270 days at £2 and 95 at `u`, giving:
+
+```
+u = 2 + grant / (F * 0.70 * 270/365)
+```
+
+Removing the cap therefore raises the benchmark yield from about £1.55 to
+£1.94 at the representative share, matching the grant-addback calculation
+in issue #1871. This assumes full grant pass-through and no demand response.
+Individual shares can differ, so a dataset aggregate need not recover the
+published grant. Caps at or above £2.75, including the £3 cap, have no effect
+relative to uncapped travel under the default £2.748 representative fare.
+The default has no fare distribution above these caps, so it cannot estimate
+the savings those caps give to passengers with higher fares. Supply
+person-specific `local_bus_uncapped_single_fare` values above a cap to model
+its effect on those passengers. Very large reductions can reach the zero-yield
+floor.
+
+## Other reform controls and limits
+
+`fare_index / prior_law_fare_index` multiplies both journey-priced and legacy
+spending. Both default to one; they are neutral reform controls rather than
+historical index series. Keep the denominator positive. `ridership_index`
+defaults to one and multiplies journey-priced spending, leaving supplied
+journey inputs intact. The model includes no demand elasticity or automatic
+ridership growth. Benchmark yields and trip translations stay nominally
+constant after 2024 unless changed explicitly. Dataset CPI-uprated household
+bus totals do not determine prices where journeys are available.
+
+A proportional scenario can set `gov.dft.bus.fare_index` to 0.9 for a 10%
+reduction. A cap scenario changes `gov.dft.bus.fares.cap`; leave the reference
+schedule and benchmark yield unchanged. Set the cap to infinity to remove it.
+The fixture-scale tests exercise both routes through UK dataset loading and
+Scenario, including baseline isolation and the January cap transitions.

myst.yml

@@ -27,6 +27,7 @@ project:
     - title: Policy
       children:
       - file: docs/engineering/excise-duties.md
+      - file: docs/engineering/bus-fares.md
       - file: docs/book/policy/model-baseline
       - file: docs/book/policy/uc-rebalancing
 site:
@@ -47,4 +48,4 @@ site:
     html_css_files:
       - style.css
   execute:
-    execute_notebooks: off
+    execute_notebooks: off

policyengine_uk/data/uprating_indices.yaml

@@ -38,6 +38,7 @@ gov.economic_assumptions.yoy_growth.obr.consumer_price_index:
 - afcs_reported
 - alcohol_and_tobacco_consumption
 - bus_fare_spending
+- bus_fare_spending_reported
 - bsp_reported
 - carers_allowance_reported
 - child_benefit_reported

policyengine_uk/parameters/gov/dft/bus/boardings_per_trip.yaml

@@ -0,0 +1,26 @@
+description: Published boardings divided by resident NTS trips in 2024-25. Scottish and
+  Northern Irish translations use the English other-local-bus trip rate as a proxy, matching
+  Microcosm. London uses all England residents because visitors also use London buses.
+metadata:
+  unit: /1
+  period: year
+  label: bus boardings per trip
+  reference:
+  - title: DfT bus statistics, BUS01 and BUS05i, 2024-25
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: DfT National Travel Survey, NTS0705a, 2024
+    href: https://www.gov.uk/government/statistical-data-sets/nts07-car-ownership-and-access
+  - title: Scottish Transport Statistics 2025, tables 2.2a and 2.8
+    href: https://www.transport.gov.scot/publication/scottish-transport-statistics-2025/chapter-2-bus-and-coach-travel/
+  - title: Northern Ireland Public Transport Statistics 2024-25, figures 3, 4 and 6
+    href: https://www.infrastructure-ni.gov.uk/publications/public-transport-statistics-northern-ireland-2024-25
+  - title: Microcosm 954, published-fact extraction and pricing derivation
+    href: https://github.com/PolicyEngine/microcosm/pull/954
+LONDON:
+  '2024-01-01': 2.369144880275
+ENGLAND_OUTSIDE_LONDON:
+  '2024-01-01': 1.12466920264
+SCOTLAND:
+  '2024-01-01': 2.145240985363
+NORTHERN_IRELAND:
+  '2024-01-01': 1.252853758464

policyengine_uk/parameters/gov/dft/bus/default_single_fare_share.yaml

@@ -0,0 +1,13 @@
+description: Share of other-local-bus fare-paying boardings paid at the point of use
+  in the 2024 National Travel Survey; used only when no person share is supplied.
+values:
+  '0001-01-01': 0.7
+metadata:
+  unit: /1
+  period: year
+  label: default single fare share
+  reference:
+  - title: DfT National Travel Survey 2024
+    href: https://www.gov.uk/government/statistics/national-travel-survey-2024
+  - title: Microcosm 954, NTS and published-receipts pricing evidence
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/fare_index.yaml

@@ -0,0 +1,13 @@
+description: Proportional multiplier on bus fares; a neutral reform lever, not a measured
+  historical fare index.
+values:
+  '0001-01-01': 1
+metadata:
+  unit: /1
+  period: year
+  label: fare index
+  reference:
+  - title: DfT bus statistics data tables, BUS01 and BUS05i
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: Microcosm 954, NTS and published-receipts pricing evidence
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/fares/cap.yaml

@@ -0,0 +1,18 @@
+description: National single-bus-fare cap on participating services in England outside London.
+values:
+  0001-01-01: .inf
+  2023-01-01: 2
+  2025-01-01: 3
+  2027-01-01: 2
+  2028-01-01: .inf
+metadata:
+  unit: currency-GBP
+  period: year
+  label: national single bus fare cap
+  reference:
+    - title: DfT evaluation of the two-pound bus fare cap, 2023 to 2024
+      href: https://www.gov.uk/government/publications/evaluation-of-the-2-bus-fare-cap
+    - title: DfT three-pound national bus fare cap, through December 2026
+      href: https://www.gov.uk/guidance/3-national-bus-fare-cap
+    - title: DfT two-pound bus fares from January to December 2027
+      href: https://www.gov.uk/government/speeches/2-bus-fares-from-january-2027

policyengine_uk/parameters/gov/dft/bus/fares/index.yaml

@@ -0,0 +1,2 @@
+metadata:
+  preserve_calendar_dates: true

policyengine_uk/parameters/gov/dft/bus/prior_law_fare_index.yaml

@@ -0,0 +1,13 @@
+description: Reference multiplier for proportional bus-fare reforms; keep positive
+  and equal to one for the published price benchmark.
+values:
+  '0001-01-01': 1
+metadata:
+  unit: /1
+  period: year
+  label: prior law fare index
+  reference:
+  - title: DfT bus statistics data tables, BUS01 and BUS05i
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: Microcosm 954, NTS and published-receipts pricing evidence
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/reference_fares/cap.yaml

@@ -0,0 +1,18 @@
+description: Fixed national cap schedule for the bus-fare yield benchmark. Read in reference_year; leave unchanged when reforming fares.cap.
+values:
+  0001-01-01: .inf
+  2023-01-01: 2
+  2025-01-01: 3
+  2027-01-01: 2
+  2028-01-01: .inf
+metadata:
+  unit: currency-GBP
+  period: year
+  label: benchmark single bus fare cap
+  reference:
+    - title: DfT evaluation of the two-pound bus fare cap, 2023 to 2024
+      href: https://www.gov.uk/government/publications/evaluation-of-the-2-bus-fare-cap
+    - title: DfT three-pound national bus fare cap, through December 2026
+      href: https://www.gov.uk/guidance/3-national-bus-fare-cap
+    - title: DfT two-pound bus fares from January to December 2027
+      href: https://www.gov.uk/government/speeches/2-bus-fares-from-january-2027

policyengine_uk/parameters/gov/dft/bus/reference_fares/index.yaml

@@ -0,0 +1,2 @@
+metadata:
+  preserve_calendar_dates: true

policyengine_uk/parameters/gov/dft/bus/reference_year.yaml

@@ -0,0 +1,13 @@
+description: Fiscal year of the published bus-fare yield benchmark, used only to price
+  the reference single-fare cap.
+values:
+  '0001-01-01': 2024
+metadata:
+  unit: year
+  period: year
+  label: reference year
+  reference:
+  - title: DfT bus statistics data tables, BUS01 and BUS05i
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: Microcosm 954, NTS and published-receipts pricing evidence
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/ridership_index.yaml

@@ -0,0 +1,13 @@
+description: Multiplier on supplied local-bus journeys; held at one without an explicit
+  ridership scenario.
+values:
+  '0001-01-01': 1
+metadata:
+  unit: /1
+  period: year
+  label: ridership index
+  reference:
+  - title: DfT bus statistics data tables, BUS01 and BUS05i
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: Microcosm 954, NTS and published-receipts pricing evidence
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/uncapped_single_fare.yaml

@@ -0,0 +1,18 @@
+description: Representative uncapped single fare inferred from the 2024-25 fare-cap grant,
+  fare-paying boardings and a 70 percent single-ticket share. Assumes no demand response
+  and full grant pass-through. This is a modelling assumption, not an observed individual
+  fare. Caps at or above GBP 2.75, including the GBP 3 cap, have no effect relative to
+  uncapped travel with this default GBP 2.748 fare. Supply person-specific
+  local_bus_uncapped_single_fare inputs to represent fares above those caps.
+  See docs/engineering/bus-fares.md.
+values:
+  '2024-01-01': 2.748019953976
+metadata:
+  unit: currency-GBP
+  period: year
+  label: assumed uncapped single bus fare
+  reference:
+  - title: DfT bus statistics, BUS01 and BUS05i, 2024-25
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: Microcosm 954, published-fact extraction and pricing derivation
+    href: https://github.com/PolicyEngine/microcosm/pull/954

policyengine_uk/parameters/gov/dft/bus/yield_per_boarding.yaml

@@ -0,0 +1,26 @@
+description: Passenger receipts divided by fare-paying boardings in 2024-25, including
+  single and season tickets. This is a benchmark yield, before subsequent cap changes and
+  explicit fare-index reforms; held nominally constant unless reformed.
+metadata:
+  unit: currency-GBP
+  period: year
+  label: bus yield per boarding
+  reference:
+  - title: DfT bus statistics, BUS01 and BUS05i, 2024-25
+    href: https://www.gov.uk/government/statistical-data-sets/bus-statistics-data-tables
+  - title: DfT National Travel Survey, NTS0705a, 2024
+    href: https://www.gov.uk/government/statistical-data-sets/nts07-car-ownership-and-access
+  - title: Scottish Transport Statistics 2025, tables 2.2a and 2.8
+    href: https://www.transport.gov.scot/publication/scottish-transport-statistics-2025/chapter-2-bus-and-coach-travel/
+  - title: Northern Ireland Public Transport Statistics 2024-25, figures 3, 4 and 6
+    href: https://www.infrastructure-ni.gov.uk/publications/public-transport-statistics-northern-ireland-2024-25
+  - title: Microcosm 954, published-fact extraction and pricing derivation
+    href: https://github.com/PolicyEngine/microcosm/pull/954
+LONDON:
+  '2024-01-01': 1.017729905895
+ENGLAND_OUTSIDE_LONDON:
+  '2024-01-01': 1.554716967657
+SCOTLAND:
+  '2024-01-01': 2.599723222144
+NORTHERN_IRELAND:
+  '2024-01-01': 2.550929922065