Heavy duty vehicle emissions inventory: where the data lives

A heavy duty vehicle emissions inventory is a modeled estimate of what an on-road truck and bus population actually emits in a defined year and place - not a list of legal limits. California's version, maintained by the California Air Resources Board, is the reference implementation most compliance teams mean when they use the phrase: the California CARB - heavy-duty vehicle emissions & inventory data record carries estimated exhaust and evaporative emissions by pollutant, broken down by vehicle category, model year, manufacturer and geographic area, with a Fleet Database rebuilt annually from state DMV registration data (the 2024 registration database powers the current build).

Two features make EMFAC unusual among the 22 primary datasets Datadory catalogs for this industry. First, geography runs deep: since January 2026 the Community-Level Heavy-Duty Vehicle Emission Inventory resolves results down to census block group rather than stopping at statewide totals. Second, the series is long by regulatory-model standards - releases run from EMFAC2007 through EMFAC2025, roughly one every one to two years. Quantities are modeled from that fleet; the rules those engines must satisfy live in separate sources.

Three records cover the emissions-and-compliance beat, and they do three different jobs. Only one models a vehicle population: California CARB - heavy-duty vehicle emissions & inventory data (quality score 7) pairs the EMFAC inventory model with a registration-derived fleet database, five live compliance reporting systems and Advanced Clean Trucks ZEV credit summaries by manufacturer and model year.

The other two publish rules rather than estimates. The EPA Emission Standards Reference Guide (quality 8) consolidates federal exhaust, evaporative and greenhouse gas standards for heavy-duty highway and nonroad engines into about a dozen fact sheets across four chapters, each carrying official EPA document numbers and Code of Federal Regulations citations - useful life, warranty period and averaging-banking-trading availability included. DieselNet's emission standards database (quality 7) is the worldwide layer: roughly 100 standards summaries spanning North America, Europe, Asia, Australia and South America, maintained continuously since 1997.

The working split: start with CARB for quantities, EPA for the federal limits an engine must meet, DieselNet the moment a fleet or customer crosses a border.

Six named fields anchor the CARB record: emissions_inventory, vehicle_population, zev_credit_balance, model_year, manufacturer and gvwr_threshold - the gross vehicle weight rating threshold that decides which fleets a program touches. Thresholds deliberately differ by program: over 8,500 lbs GVWR under Advanced Clean Fleets, over 14,000 lbs under Clean Truck Check, and off-road diesel equipment of 25 hp or greater under DOORS, so one dump truck can plausibly sit inside three programs at once.

Compliance data flows through the TruckStop portal's five reporting systems: TRUCRS (Advanced Clean Fleets and Truck & Bus), Clean Truck Check (CTC-VIS), Off-Road Diesel (DOORS), Advanced Clean Trucks (ACTRS) and Transport Refrigeration. ACT credit summaries arrive as web fact-sheet tables split by manufacturer and model year, derived from ACTRS filings - there is no machine-readable export, so budget transcription time. Formats across the whole record are zip, html and pdf.

Freshness behaves differently above and below the model layer. Releases land every one to two years, the Fleet Database refreshes annually from DMV registrations, and compliance milestones move faster still: the Truck & Bus Regulation has required 2010 or newer engines in diesel vehicles over 14,000 lbs GVWR since January 1, 2023, with non-compliant vehicles refused DMV registration. One legal caveat belongs in every deliverable - some EMFAC2025 outputs reflect federal waiver actions under litigation and are flagged as not yet US EPA approved for SIP and transportation conformity purposes.

An inventory explains emissions; registries explain the fleet producing them, and joining the two is where this slice earns its keep. Two US denominators wire in cleanly:

• FHWA Highway Statistics (quality 9, commercial delivery terms): the MV-series state truck registration tables cover all 50 states plus DC, with annual editions back to 1945 and open-data trend tables reaching 1900; MV-1 alone spans roughly 50 states x 4 vehicle categories x 2 ownership classes x 125 years.
• NHTSA vPIC API (quality 9): decode VINs into GVWR class, engine and plant of manufacture - 12,340 makes, 154 variables per decode, no integration key, plus monthly SQL snapshots around 335 MB uncompressed. That turns a client's VIN list into exactly the weight classes CARB programs key on.