What is Solvent Streets?
Solvent Streets is a planning-grade pavement estimator. It aggregates OpenStreetMap pavement geometry into a hex grid, applies an exponential Pavement Condition Index (PCI) decay model per road classification, projects treatment costs from PCI-banded cost tiers, and simulates multi-year maintenance budget scenarios.
It is not a substitute for field-measured pavement surveys or a formal asset-management system — its outputs should be read as order-of-magnitude planning inputs rather than engineering specifications.
Examples
Each example uses a different configuration. Select one to explore an interactive dashboard with maps, forecasts, and cost projections.
Bay Area, CA
Denver Metro, CO
Greater Boston, MA
Livermore, CA
Los Angeles, CA
Portland Metro, OR
Top 50 Cities
Methodology
This section describes the data sources, models, and assumptions behind the analysis presented in each dashboard.
Data sources
- Road, parking, and sidewalk geometry. OpenStreetMap via the Overpass API, under the Open Database License (ODbL). When a city has no ArcGIS or local-layer source configured, OSM is the sole source and coverage inherits OSM's gaps — most notably uneven sidewalk tagging and inconsistent classification of alleys and unpaved service roads.
- Jurisdictional layers. Optional ArcGIS FeatureService endpoints
configured per city in
pvmt.toml. - City boundaries. Nominatim lookups or user-supplied GeoJSON, configurable per city.
- Initial PCI. A stand-in value supplied through config or the interactive slider. PVMT does not ingest field-measured PCI and makes no claim that the starting condition matches reality — changing this input is the right way to explore sensitivity to unknown starting condition.
The exact sources and endpoints used for a given example are listed in that example's Config tab.
Decay model
Each road classification decays independently via
PCI(t) = PCI₀ · exp(−k · t)
where k is an annual decay constant that depends on the road
classification. Higher-class roads (motorway, trunk, primary) decay more
slowly than lower-class roads (residential, service) because they are
built to thicker, more rigorous design standards and typically receive
more frequent maintenance. Default values are derived from LTPP data
reported in FHWA-RD-01-156, Long-Term Pavement Performance and
ship as part of the forecast package; they are continental-US
averages and do not account for local climate, traffic, or
construction quality. A config may set a per-city decay_rate to tune
for local conditions (e.g. freeze/thaw or road salt); that override is
applied as the rate for a typical road and scales every road class
proportionally, so the per-class ordering (higher classes decay slower)
is preserved rather than flattened. Sidewalks
decay on a separate, slower track and are not treated as a highway class.
Cost model
Treatment costs are banded by PCI: each band has a representative
$/sq m value, and costs between bands are linearly interpolated at the
tier midpoints, so the cost-versus-PCI curve is smooth rather than
step-shaped. Above the highest anchor (the midpoint of the preventive
tier) and below the lowest anchor (the midpoint of the reconstruction
tier), the cost is clamped to that anchor's value rather than
extrapolated. Default cost tiers are expressed in $/sq m and sourced
from FHWA treatment-selection guidance; they are calibration inputs, not
measurements, and local bid prices will differ. Roads and sidewalks use
independent cost tiers because the treatment economics differ
substantially.
Scenario comparisons
PVMT ships with three comparison runs driven by annual funding level, all using the worst-first allocation strategy (budget is spent on the lowest-PCI segments first):
- 25% funding — annual spend = 25% of year-1 worst-first need.
- 50% funding — annual spend = 50% of year-1 worst-first need.
- Full funding — unconstrained budget; spend whatever it takes to treat every segment that falls below the worst-first trigger each year.
A do-nothing baseline (no spend, uncontrolled decay) is shown alongside the funded runs for comparison.
The forecast library also implements a preventive-first strategy (prioritize highest-PCI segments that are still in the preservation window), but the default UI comparisons do not exercise it. Preventive vs. worst-first allocation is governed by per-strategy efficiency multipliers; those multipliers are illustrative calibration constants chosen to reflect the direction and sign of the effect reported in FHWA-HIF-12-042, Pavement Preservation: Preserving our Investment — that $1 of preventive maintenance is reported to avoid $6–$10 of future reconstruction — not to reproduce that benefit-cost ratio as a single-year spending efficiency.
Area growth
Optional compound annual growth applies to pavement area each year:
Area(y) = Area₀ · (1 + g)^y
where g is configured per city (default zero). This lets an example
model a city that is still expanding its street network; it does not
model demolition or removal.
Solvency metrics (streets/roads only)
The dashboard's Financials headline and the cross-city leaderboard report three solvency figures. They are computed on the roads/streets cohort only — the aggregate scenarios blend roads, parking, and sidewalks but cost the blend at road tiers, which would mis-price sidewalks, so an absolute dollar claim must be roads-only. They are derived from a worst-first run at the city's configured annual budget.
-
Insolvency year — the first forecast year in which the cumulative deferred backlog reaches one full year of network-treatment need (the year-1 need: the cost to treat the entire network once). Because the deferred backlog is a monotonically non-decreasing accumulator (see below), once a city is a whole network-treatment behind it does not recover within the model, so this is the "unrecoverable" threshold. A city whose backlog never reaches it is reported as solvent through the horizon. This is deliberately not "the first year need exceeds spend": year-1 need is the cost to treat the entire network, far above any real budget, so that test trips in year 1 for virtually every city and cannot distinguish a slightly-underfunded city from a badly- underfunded one. Reported only when a current budget is configured.
-
Hold-steady (break-even) budget — the smallest constant annual budget whose final deferred backlog is within a small relative tolerance (a fraction of year-1 need) of zero. Found by bisection over budget; the search's upper bound is the peak do-nothing annual need over the horizon, which is sufficient to fully fund every year.
-
Funding gap —
(break-even − current budget) / current budget, the primary cross-city ranking metric. Negative when a city already budgets at or above its hold-steady level. Reported only when a current budget is configured.
Three caveats apply to these figures specifically:
- The deferred backlog is cumulative unmet need, not a recoverable balance. It only ever grows; spending in a later year reduces new need but never pays down backlog already accrued. Read it as "total treatment value foregone to date," not as a debt that can be cleared.
- In the years before the insolvency crossing, the reported
annual_spendseries can exceed the configured budget. The allocator routes leftover budget on a fully-funded cohort into extra PCI recovery (a surplus branch), and that extra is counted as spend. So anannual_spendabovecurrent_budgetin early years is expected, not an error. - Break-even assumes the cost-versus-PCI relationship is monotone
(true for the default cost tiers: worse pavement costs more to treat).
A pathological custom
cost_tierscurve that violates this could make the bisection overstate the break-even budget — a conservative direction (it never understates the gap).
Assumptions and limitations
- Initial PCI is a user-chosen stand-in, not a field measurement.
- Decay-rate defaults are continental-US averages; local climate, traffic, and construction quality shift the true values.
- Hex aggregation loses sub-hex heterogeneity — a hex with one badly deteriorated street and three good ones looks like a moderately deteriorated hex.
- No network effects are modeled (detours, closures, access externalities, project bundling).
- All costs are in today's dollars. No inflation, discounting, or present-value adjustment is applied.
- Treatment effectiveness is modeled as an efficiency multiplier on spend, not as a deterministic post-treatment PCI bump.
- Output is a planning-grade estimate, not an engineering specification.
References
- FHWA-RD-01-156 — Long-Term Pavement Performance, Federal Highway Administration. Source for per-class decay-rate defaults.
- FHWA-HIF-12-042 — Pavement Preservation: Preserving our Investment, Federal Highway Administration. Motivates the direction of the preventive-first vs. worst-first efficiency adjustment.
- OpenStreetMap contributors — road, parking, and sidewalk geometry (ODbL).
- pvmt source —
implementation reference. See
docs/architecture.mdfor the ingest and compute pipeline.