Support Activities for Transportation (United States) — NAICS 488

A Histometrics rollup primer for both public-market and private investors, synthesized from the six child industry-group primers and our federal ground-truth statistics for this level.

(NAICS = North American Industry Classification System, the U.S. government's standard scheme for grouping businesses by what they do. This page covers 488, a three-digit subsector inside Sector 48–49, Transportation and Warehousing. It rolls up the six four-digit industry groups beneath it — 4881 through 4889 — and its real value is the contrast across them.)

1. Overview

Support Activities for Transportation is the services-and-infrastructure layer that stands behind every mode of moving goods and people — the firms that service the aircraft, run the airports, switch and repair rail cars, load the ships and pilot them in, tow the trucks and run the toll roads, and — biggest of all — arrange freight without owning any vehicle at all. It is the "picks-and-shovels" tier of American transportation: recurring, often mandatory, often toll-like work sold into cyclical air, rail, water, road, and freight markets [1][4][6].

The subsector bundles six very different businesses. Five of them are asset-heavy or infrastructure-anchored — airports, ports, toll roads, rail terminals, LNG (liquefied natural gas) docks — where the strategically important pieces are usually owned by governments or by private infrastructure capital, and where no U.S.-listed pure-play exists. The sixth, freight arrangement (the broker/forwarder middleman), is the opposite: asset-light, the largest child by revenue, the most fragmented, and the only one where public-market investors can buy a genuine listed pure-play [4][5][6][7][8][9].

That single fact frames the whole primer. Where the reported revenue is (freight brokering, ~60% of the subsector) is not where the durable moats are (the government-owned and infrastructure-owned physical assets), and neither cleanly matches where public equity is available. Read 488 as an ecosystem, not a company — and always decompose it child by child before drawing a conclusion.

2. What's inside — the six children and how they differ

The subsector splits by transport mode (air, rail, water, road) plus two mode-agnostic boxes (freight arrangement and an "everything else" residual). They share the same idea — get paid to help someone else's cargo or passengers move — but as investments they behave completely differently. Ordered by revenue share:

Receipts and shares are 2022 Economic Census; jobs shares are 2023 County Business Patterns (see §3). Percentages are computed against this level's ground-truth totals [2][3].

How to read the split. Three structural divides run through the table:

• Asset-light middleman vs. asset-heavy infrastructure. Freight arrangement (4885) owns nothing but people, software, and relationships — so it scales cheaply, carries almost no listed competition worth the name, and its main assets walk out the door each night. The other five children sit on expensive, long-lived, often irreplaceable physical assets (runways, berths, dredged channels, toll lanes, rail yards, LNG docks) or the licensed franchises attached to them.
• Who owns the strategic core. In four of the modal children, the single most valuable pieces are governmental — airport authorities and the FAA (Federal Aviation Administration) in air; public port authorities in water; state/local toll authorities in road; and, for rail, the Class I railroads that do most switching and car repair in-house (counted under rail transportation, NAICS 482, not here). Federal business statistics exclude governments, so those cores are largely invisible in the numbers below and unbuyable in public markets [4][6][7].
• Where public equity actually exists. Genuine U.S.-listed pure-plays live almost entirely in 4885 (freight brokers/forwarders such as C.H. Robinson and Expeditors), with a thin second pocket in 4881 (independent MRO — StandardAero, AAR, VSE — mostly listed only in the last few years) and an energy-flavored third in 4889 (LNG exporters). Everywhere else, listed exposure is a proxy: a foreign airport or toll operator, a shipping line with a terminal stake, a rail-car lessor, or a diversified parent.

The through-lines that unite them. Every child earns on derived demand — it gets paid only when something else moves (a plane, a ship, a rail car, a truck, a container). Every child shows local concentration inside national fragmentation — one dominant airport or port or toll road per metro, but thousands of firms nationwide. And in every child the same two forces are consolidating the tail: private-equity and infrastructure funds rolling up small operators, and asset owners (airlines, railroads, carriers, shippers) deciding whether to do the work in-house or outsource it.

3. Size (this level's rollup figures + undercount caveat)

The figures below are OUR ingested federal-statistics extract for NAICS 488, drawn from the Census Bureau's 2022 Economic Census concentration program (receipts, firms, concentration) and 2023 County Business Patterns (CBP — establishments, employment, payroll).

(CR4/CR8/CR20/CR50 = combined revenue share of the largest 4/8/20/50 firms. HHI = a market-concentration index that sums firms' squared revenue shares; U.S. antitrust agencies treat anything under 1,500 as "unconcentrated." Receipts and concentration are 2022; employment and payroll are 2023 — do not compare receipts against same-year payroll.)

Within their own years these imply roughly $5.9 million of receipts per firm, about 17 employees per establishment, and ~$66,800 of pay per employee — a blended average that spans a very wide range: from ~$49,300 in road support (low-wage towing) to ~$88,600 in water (unionized longshore labor and licensed harbor pilots), with skilled air MRO and white-collar freight brokering in between [3][6][7].

The children reconcile — but the headline receipts number is not apples-to-apples. The six children add up cleanly to this level:

Establishments (49,494) and employees (853,486) reconcile to the unit; receipts sum to ~$223.9B against the $223.92B total; payroll sums to ~$57.0B against $57.02B [2][3]. (Firms are the one exception: the children list 38,031 against a subsector total of 37,886, because ~145 operators that span more than one child are counted once at the 488 level.) But two cautions apply before comparing the receipts column. First, freight arrangement's ~$134.9B mixes net and gross: brokers typically report only the spread they keep, while forwarders that take contractual responsibility for the freight may report gross billings including the carrier cost passed through — so 4885's dollar figure is inflated relative to the fee-based children, and its true economic weight is smaller than 60% [8]. Adjust for that and the asset-heavy modal children matter more than raw receipts suggest.

The concentration statistic is real but misleading. The subsector HHI of 19.3 is one of the lowest readings in the entire U.S. economy — and it is lower than every child except road support. That is an artifact of aggregation: pooling six activities whose leading firms are entirely different companies (a freight broker does not compete with a harbor pilot, a tow operator, or a jet-engine shop) mechanically dilutes every share. The group number therefore understates real market power, and it buries genuine local monopolies (one airport, one port, one toll road, one pilot group per gateway) and a tight air-traffic-control oligopoly inside 4881. Never read this subsector's concentration as one number — decompose it child by child, and within each child, gateway by gateway [4][6].

Undercount caveat — the biggest number here is what's missing. These are private employer business statistics. They systematically exclude, across all six children:

• Government operators — the strategic core of four modes. CBP and the Economic Census largely omit government establishments, but the biggest operators of the physical backbone are governments: public airport authorities and the FAA's air-traffic system (4881); public port authorities, vessel-traffic services, and locks (4883); state and local toll authorities, which collect well over $15 billion a year (4884); and the Class I railroads whose in-house switching and car repair land under NAICS 482 (4882) [4][6][7].
• The self-employed and nonemployer tail. One-truck towing sole proprietors, harbor pilots (organized as partnerships whose earnings flow out as distributions, not payroll), one-person marine surveyors, home-based 1099 freight agents, and small crating shops are undercounted or absent [6][7][8][9].
• Activity booked under other codes. Airline maintenance done in-house, factory overhaul by manufacturers, and fuel sold as wholesale (4881); LNG and pipeline terminals booked under their energy parents (4889); and much brokerage revenue embedded inside asset-based carriers and tech platforms (4885) [4][8][9].

So read the $223.9 billion as "the private, employer, third-party transportation-support economy," not "U.S. transportation support." The wider systems these firms serve are an order of magnitude larger — U.S. commercial airports alone anchor an estimated ~$1.8 trillion economic footprint and seaborne trade moves over $2.28 trillion of goods a year [4][6]. OUR data do not report subsector margins, capital spending, utilization, or valuation multiples; where those appear below they come from the cited child primers and industry sources.

4. Investable universe — where value concentrates across the children

Value in 488 is lopsided and mostly off-exchange, and it concentrates in different places than the revenue does. The public-equity map has essentially three pockets and one big gap:

• Pocket 1 — freight arrangement (4885), the asset-light majority. This is the one child with a real listed presence: C.H. Robinson (Nasdaq: CHRW) and Expeditors International (Nasdaq: EXPD) are the closest to pure-plays, with brokerage-heavy-but-diversified exposure through RXO (NYSE: RXO), Landstar (Nasdaq: LSTR), Hub Group (Nasdaq: HUBG), ArcBest (Nasdaq: ARCB), and Forward Air (Nasdaq: FWRD), plus embedded exposure inside J.B. Hunt, Uber, UPS, and FedEx. The #2 broker, Total Quality Logistics (TQL), is founder-owned, and PE roll-ups dominate the mid-market [8].
• Pocket 2 — independent air MRO (inside 4881). Recently listed technical-aftermarket names — StandardAero (NYSE: SARO), AAR Corp. (NYSE: AIR), and VSE Corp. (Nasdaq: VSEC) — are the only listed pure-plays on the asset-heavy side of the whole subsector, with handling/services exposure via ABM, SATS, Agility Global, and General Dynamics (Jet Aviation) [4].
• Pocket 3 — energy-labeled terminals (inside 4889). LNG and pipeline terminals reach public markets only under energy names — Cheniere (NYSE: LNG), Cheniere Partners (NYSE: CQP), Venture Global (NYSE: VG), and midstream operators — not as "transportation support" [9].
• The gap — water, road, rail, and the airport core. There is no U.S.-listed pure-play in port/terminal operations, marine cargo handling, harbor towage, toll roads, or rail switching/repair. The strategic assets are governmental or privately held. Public-market investors reach them only through proxies: foreign airport operators (e.g., ASUR, AENA, ADP), foreign toll operators (Ferrovial, Transurban, VINCI, Atlas Arteria), a foreign towage stock (Svitzer), a shipping line with a terminal stake (Matson), energy-midstream terminal owners (Kinder Morgan), rail-car lessors and aftermarket names (GATX, Trinity, Wabtec, Greenbrier), diversified infrastructure vehicles (Brookfield Infrastructure), and federal systems contractors for ATC modernization (RTX, Leidos) [4][5][6][7].

Where the real U.S. money actually lives — private and fixed-income.

• Private-equity and infrastructure funds own the FBO networks, port and cargo terminals, harbor-tug fleets, toll concessions, rail terminals, and independent MRO/handling platforms — Blackstone, KKR, Apollo, GIP/BlackRock, CPP Investments, Brookfield, IFM, Macquarie, and peers treat these toll-like assets as core infrastructure holdings [4][6][7].
• Municipal revenue bonds are the most direct retail-accessible way to lend to the government-owned cores: airport revenue bonds and port revenue bonds, repaid from ring-fenced airport/port cash flows [4][6].
• Direct small-business ownership is a genuine path in the fragmented tails — a single tow company, repair station, FBO, crating shop, switching operation, or freight brokerage — most under the U.S. Small Business Administration (SBA) size lines and eligible for SBA-backed acquisition financing [7][8][9].

(Tickers, exact stakes, and full company tables live in the six child primers; treat any listed name as a minority-exposure vehicle and diligence how much revenue is genuinely tied to U.S. transportation support.)

5. How the money works

There is no single 488 business model; the subsector runs on five recurring earnings engines, and most children mix more than one:

• Asset-light spread (dominant in 4885). Buy transport capacity from a carrier, sell it to a shipper, keep the difference. Earnings scale with loads × spread per load, financed through a pay-carrier-fast / collect-from-shipper-slow cash cycle. Counter-intuitively, broker margins are often widest when freight is soft and capacity is cheap — the freight cycle, not raw volume, drives profit [8].
• Fee-for-service labor + parts markup (MRO, rail-car repair, crating, surveyors, handling). Bill technician or crew hours at a shop rate plus a markup on parts. Profit turns on skilled-labor productivity, utilization, and — for maintenance — the fact that inspection and overhaul are mandatory on regulator-set schedules, giving the work an annuity-like floor [4][5][9].
• Toll / throughput on scarce fixed assets (airports, ports, toll roads, LNG docks, transload, FBO fuel). Charge per passenger, per container/ton, per vehicle, per gallon uplifted, or per barrel of capacity. Very high incremental margins once the asset is built, heavily debt-financed, closer to a toll road than a growth stock — which is exactly why infrastructure funds pay billions for the networks [4][6][7][9].
• Compulsory / mandated services (pilotage, salvage retainers, tank-car requalification, mandatory inspections, contract-tower staffing). Demand is set by law rather than by the market, which makes it steadier than the underlying traffic — a defensive base layer running through several children [4][5][6].
• Government-procurement contracts (contract air-traffic towers, some rail/road work). Revenue is essentially (units under contract) × (staffing) × (rate), won and lost at recompete rather than in a market [4].

The common financial trait across the asset-heavy children is high fixed cost and operating leverage: dredged channels, runways, cranes, tugs, toll lanes, and dry docks are paid for before the volume arrives, so incremental traffic drops heavily to the bottom line — and downturns hurt disproportionately. The common trait across the whole subsector is derived, non-discretionary demand: much of this work must happen for cargo and passengers to move at all.

6. Demand drivers

Every child ultimately rides the physical movement of goods and people, then splits into mode-specific tailwinds:

• The goods economy and the freight cycle — manufacturing, wholesale, retail, inventory restocking, and imports drive freight arrangement, rail support, and cargo handling; the rate cycle (capacity entering and leaving) can matter more than volume [8].
• Trade volume and routing — over $2.28 trillion of U.S. seaborne trade, container import cycles, tariff-deadline timing that pulls cargo forward, and Panama/Suez reliability reshuffle which gateways and modes win [6].
• Passenger and business-jet travel — enplanements track GDP and employment (airports, handling, concessions); U.S. private-jet activity is running ~29% above 2019, feeding FBOs [4].
• Aging fleets and outsourcing — older aircraft and rail cars need more maintenance, and asset owners (airlines, railroads, carriers) keep outsourcing non-core work to third-party support firms — a structural feed to MRO, handling, and rail repair [4][5].
• Infrastructure capital and federal budgets — a record ~$28B/year U.S. airport capital cycle and a multi-billion-dollar ATC-modernization program (air), USACE channel dredging (water), and the toll/P3 pipeline (road) drive the asset-heavy children — and expose them to government-funding risk [4][6][7].
• Energy and bulk cycles — Gulf Coast LNG and petrochemical export buildout spins off long-dated tug-escort, terminal, and tank-car work; the U.S. exported a record ~111 million metric tons of LNG in 2025, with exports projected up ~30% by 2027 [6][9].
• Mandated demand — compulsory pilotage, salvage retainers, tank-car requalification clocks, and mandatory inspections put a legal floor under a meaningful slice of activity [5][6].

Demand is durable but cyclical: recessions, fuel spikes, freight downturns (the 2022–25 freight recession was among the longest on record), and travel shocks all bite, and individual gateways and firms can lose share even when the mode grows [6][8].

7. Regulation

There is no single regulator — each mode answers to its own agencies — but the same patterns recur across all six children.

• By mode: air sits under the FAA (Part 139 airports, Part 145 repair stations, air-traffic control) [4]; rail under the STB (Surface Transportation Board, economic regulator), FRA (Federal Railroad Administration, safety), and PHMSA (Pipeline and Hazardous Materials Safety Administration, tank cars) [5]; water under the FMC (Federal Maritime Commission), USCG (U.S. Coast Guard), USACE (U.S. Army Corps of Engineers), and state pilotage boards [6]; road under state/local licensing plus the FMCSA (Federal Motor Carrier Safety Administration) [7]; freight arrangement under the FMCSA (a $75,000 broker surety bond, with a stricter financial-responsibility rule effective January 16, 2026), the FMC, and Customs [8][10]; and the residual bin under DOE/FERC for LNG and CMS/state Medicaid for NEMT (non-emergency medical transportation) [9].
• Common threads: (1) licensing and certification as barriers to entry — Part 145 certificates, A&P mechanic licenses, AAR tank-car shop certification, pilot licenses, broker bonds — which are a cost to newcomers and a moat for incumbents; (2) cabotage and the Jones Act (the Merchant Marine Act of 1920, requiring U.S.-built/-flagged/-crewed coastwise vessels), which walls off harbor towage from global competitors [6]; (3) government ownership of the core assets, which caps how much value private capital can extract and injects policy risk; and (4) anti-diversion / ring-fencing rules (e.g., airport and port revenue must stay on the airport/port) that make revenue bonds creditworthy [4][6].

The investor takeaway: these are permission-dependent, moat-protected businesses. Regulation simultaneously creates the franchises, walls out competitors, and caps pricing — and a government shutdown or continuing resolution can freeze FAA hiring, airport grants, and modernization spending across the whole air child at once [4].

8. Consolidation

The subsector is fragmented nationally but consolidating steadily, through two mechanisms that recur in every child:

• Financial roll-ups of the fragmented tail. Private-equity and infrastructure funds are assembling the small operators behind hard local barriers (airport leases, hangar scarcity, berth rights, pilotage authority, toll concessions, rail interchange): FBO and handling platforms (Signature, Atlantic, Swissport) [4]; port and terminal operators (Ports America/CPP, SSA-Carrix/Blackstone) and harbor-tug fleets [6]; toll concessions among a small global club (IFM, Macquarie, Meridiam) plus towing and sweeping roll-ups [7]; rail switching/terminal operators (Watco; Genesee & Wyoming, taken private by Brookfield/GIC for $8.4B) [5]; and freight-brokerage roll-ups (RXO/Coyote, WWEX, Echo) [8].
• Vertical integration by asset owners. Shipping lines run their own terminals (Maersk/APM, MSC/TIL, COSCO), Class I railroads keep switching and car repair in-house, and asset-based carriers bolt on brokerage arms — each deciding to own the support activity rather than buy it [5][6][8].

IPOs are the exception, not the rule — the recent independent-MRO listings (StandardAero in 2024) are a notable break — which is precisely why so few listed pure-plays exist: infrastructure and PE owners trade these assets among themselves rather than floating them. And the national fragmentation (HHI 19.3) hides local monopoly everywhere: one dominant airport, port, toll road, or pilot group per gateway, plus a genuine air-traffic-control oligopoly inside 4881 [2][4][6].

9. Risks

• Cyclicality and shock exposure (whole subsector). Demand falls with recessions, freight downturns, fuel spikes, tariff whiplash, geopolitics, and travel shocks; COVID-19 and the 2022–25 freight recession hit multiple children at once [6][8].
• Measurement / classification risk. The NAICS label is a poor size guide: it misses government operators, nonemployers, and activity booked in adjacent codes, and it mixes net and gross receipts — so anyone using 488 (or a single child) as an investment screen will misjudge both the size and the real players (§3) [2][3].
• A two-sided labor problem. Low-wage, high-turnover ramp, towing, and handling labor at one end; a structural scarcity of skilled A&P mechanics, air-traffic controllers, harbor pilots, and mariners at the other — both wage inflation and skilled scarcity can absorb the benefit of higher volumes [4][6].
• Leverage and interest-rate sensitivity. PE- and infrastructure-owned FBOs, terminals, toll roads, tug fleets, and rail platforms carry heavy debt; higher rates raise refinancing costs and compress equity returns [6][7].
• Government-funding and policy dependence. Airport grants, ATC modernization, channel dredging, and toll authority all hinge on federal and state budgets and law; shutdowns, rate caps, and re-legislation of pilotage/Jones Act/toll rules are live risks [4][6].
• Labor disruption and single-point failure. Dockworker strikes (the October 2024 East/Gulf stoppage), the 2024 Baltimore bridge collapse, and airport/ATC outages show how physically concentrated and disruption-prone these assets are [6].
• No pure-play in five of six children. Public exposure must be underwritten asset-by-asset, not off a diversified parent's total revenue — and the listed proxies carry currency, liquidity, and unrelated-segment risk [4][6][7].
• Structural threats by child — OEM (original-equipment-manufacturer) encroachment into air MRO; disintermediation, fraud, and double-brokering in freight arrangement; commodity concentration (coal decline) and Class I bargaining power in rail; permitting/reimbursement risk in the LNG/NEMT residual [4][5][8][9].

10. How to invest & outlook

The subsector is bimodal for investors, and the split is the whole strategy.

• Public equity, direct — realistically available only in freight arrangement: C.H. Robinson (Nasdaq: CHRW) and Expeditors (Nasdaq: EXPD) as the closest pure-plays, with brokerage-heavy diversified exposure via RXO, Landstar, Hub Group, ArcBest, and Forward Air. These trade as freight-cycle and goods-economy proxies [8]. Secondary pockets: independent air MRO (SARO, AIR, VSEC) [4] and LNG-labeled terminals (LNG, CQP, VG) [9].
• Public equity, proxy — for the asset-heavy children, reach the theme through foreign airport operators (ASUR, AENA, ADP), foreign toll operators (Ferrovial, Transurban, VINCI, Atlas Arteria), a foreign towage stock (Svitzer), rail-car lessors and aftermarket (GATX, Trinity, Wabtec, Greenbrier), energy-midstream terminal owners (Kinder Morgan), diversified infrastructure vehicles (Brookfield Infrastructure), and ATC systems contractors (RTX, Leidos). In every case, check what share of earnings is actually tied to U.S. transportation support [4][5][6][7].
• Fixed income — municipal airport and port revenue bonds are the large, liquid, retail-accessible way to lend to the government-owned cores, backed by ring-fenced revenue; underwrite the specific gateway's traffic, contracts, and debt-service coverage [4][6].
• Private markets — where most U.S. value actually lives — infrastructure and PE funds own the FBOs, terminals, toll roads, tug fleets, rail platforms, and MRO/handling businesses; and the fragmented tails offer a genuine direct small-business path (a tow company, repair station, FBO, crating shop, or brokerage, most SBA-financeable) [4][6][7][8][9].

What to diligence: concession term and minimum-volume commitments; owned-vs-leased capacity; union agreements and automation clauses; contract structure and single-customer/recompete risk; leverage and refinancing terms; the durability of federal/state funding; and — for any listed name — how much revenue is truly tied to U.S. transportation support versus a larger, differently-driven parent.

Outlook (forward-looking judgment, not a guarantee). As an asset class, U.S. transportation support is a defensive, derived-demand, infrastructure-flavored exposure that grows with trade and travel over cycles and is being professionalized by roll-up capital. The children point in different directions for different reasons: freight arrangement is in early-cycle recovery after a historic freight recession, cyclical and technology-pressured but the most publicly accessible [8]; air rides an aging-fleet MRO wave, a record airport capital cycle, and ATC modernization — the most favorable structural setup, and the one with new listed pure-plays [4]; water is flat-to-soft near term on tariff uncertainty but defensively locked by labor peace and a Gulf LNG tailwind [6]; road is slow, defensive, and roll-up-friendly [7]; rail is flat-to-cyclical with a proposed Class I mega-merger as the wildcard [5]; and the residual bin is a split verdict — small cyclical crating shops beside a booming LNG build-out [9]. The base case for the subsector as a whole is a well-funded, derived-demand infrastructure decade sitting on a public and private backbone that is mostly not listed. The classic mistake is treating trade or traffic growth as sufficient: contract structure, leverage, labor scarcity, government funding, and — above all — which child and which asset you actually own decide how much of that growth becomes investor cash flow. Underwrite the six halves separately; the NAICS label is a map, not a ticker.

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Sources

Ground-truth federal figures for NAICS 488 come from our ingested dataset (stats-488.md): receipts, firm count, and CR4/CR8/CR20/CR50 + HHI from the 2022 Economic Census — Concentration; establishments, employment, and annual/Q1 payroll from County Business Patterns 2023. All qualitative detail is synthesized from the six child primers, whose full numbered Sources lists apply. Numbering is specific to this rollup.

1. U.S. Census Bureau, "2022 NAICS Manual / Definitions — 488 Support Activities for Transportation and its six industry groups (4881–4889): scope, inclusions, and cross-references to rail transportation (482), automotive repair (8111), warehousing, and manufacturing." https://www.census.gov/naics/?year=2022
2. U.S. Census Bureau, 2022 Economic Census — Concentration by Largest Firms, NAICS 488 (receipts $223,924,385K; 37,886 firms; CR4 6.0%, CR8 10.0%, CR20 15.8%, CR50 25.1%; HHI 19.3). [Histometrics ground-truth dataset, stats-488] https://www.census.gov/programs-surveys/economic-census/data/tables.html
3. U.S. Census Bureau, County Business Patterns 2023 — NAICS 488 (establishments 49,494; employment 853,486; annual payroll $57,019,820K; Q1 payroll $14,286,426K) and CBP methodology on government/nonemployer/self-employed exclusions. [Histometrics ground-truth dataset, stats-488] https://www.census.gov/programs-surveys/cbp.html
4. Histometrics industry-group primer 4881 — Support Activities for Air Transportation (receipts ~$38.2B; 245,625 employees; airport authorities + FAA excluded; MRO, FBO, ground handling, ATC modernization; listed MRO SARO/AIR/VSEC; muni airport bonds; PE/infra and foreign airport equities). [Histometrics primer-4881]
5. Histometrics industry-group primer 4882 — Support Activities for Rail Transportation (receipts ~$7.6B; 49,372 employees; single child 48821; Class I in-house work counted under NAICS 482; STB/FRA/PHMSA/AAR; PE/infra roll-ups Watco, Genesee & Wyoming/Brookfield-GIC; UP–NS merger wildcard). [Histometrics primer-4882]
6. Histometrics industry-group primer 4883 — Support Activities for Water Transportation (receipts ~$22.7B; 101,459 employees; four children; public port authorities + pension/infra funds + foreign carrier terminals; compulsory pilotage, Jones Act, OPA-90; muni port bonds; ~$2.28T seaborne trade; ILA/PMA labor peace). [Histometrics primer-4883]
7. Histometrics industry-group primer 4884 — Support Activities for Road Transportation (receipts ~$17.1B; 109,993 employees; towing ~70% + toll/other ~30%; government toll authorities excluded, >$15B/year; foreign toll operators Ferrovial/Transurban/VINCI; tolling tech; PE roll-ups). [Histometrics primer-4884]
8. Histometrics industry-group primer 4885 — Freight Transportation Arrangement (receipts ~$134.9B; 324,765 employees; single child 48851; asset-light broker/forwarder spread; listed pure-plays CHRW/EXPD plus RXO/LSTR/HUBG/ARCB/FWRD; TQL founder-owned; net-vs-gross receipts caveat; 2022–25 freight recession). [Histometrics primer-4885]
9. Histometrics industry-group primer 4889 — Other Support Activities for Transportation (receipts ~$3.4B; 22,272 employees; single child 48899; packing & crating ~97% of firms vs. residual LNG/pipeline/NEMT bin; energy names Cheniere/CQP/Venture Global; ISPM-15/DOE/FERC/CMS oversight). [Histometrics primer-4889]
10. Federal Motor Carrier Safety Administration, "Broker and Freight Forwarder Financial Responsibility Rule" (effective Jan. 16, 2026) and $75,000 broker surety-bond requirement. [via Histometrics primer-4885] https://www.fmcsa.dot.gov/registration/broker-and-freight-forwarder-financial-responsibility-rule-overview-and-compliance
11. International Longshoremen's Association / United States Maritime Alliance master contract (through Sept. 30, 2030) and Pacific Maritime Association / ILWU Pacific Coast Longshore Contract (2022–2028). [via Histometrics primer-4883] https://ilaunion.org/
12. Federal Aviation Administration, "Brand New Air Traffic Control System" fact sheet (2025) and Airports Council International–North America airport-capital and economic-impact studies (~$28B FY2025 capital spending; ~$1.8T footprint). [via Histometrics primer-4881] https://www.faa.gov/newsroom/brand-new-air-traffic-control-system-bnatcs-fact-sheet
13. Association of American Railroads, "Weekly Rail Traffic — 52 weeks of 2025" (25,564,700 combined carloads + intermodal units, +1.5% year over year). [via Histometrics primer-4882] https://www.aar.org/news/
14. U.S. Energy Information Administration, "U.S. natural gas exports to grow nearly 30% by 2027 as LNG facilities ramp up" (record ~111 million metric tons of LNG exported in 2025). [via Histometrics primer-4889] https://www.eia.gov/todayinenergy/
15. Federal Aviation Administration and municipal-market practice — airport and port revenue bonds (general airport/port revenue bonds; revenue anti-diversion / ring-fencing) as the retail-accessible debt route onto government-owned transportation infrastructure. [via Histometrics primers 4881 and 4883] https://www.faa.gov/airports/aip/grant_assurances