Why do freight indexes matter for economic forecasting?
Freight indexes track the physical movement of goods through trucking, rail, intermodal and air freight. Because freight precedes consumption and inventory adjustments, indexes like the Cass Freight Index and the BTS Transportation Services Index serve as cyclical signals. Their representativeness has weakened as services have come to dominate developed-economy GDP.
In this article
The short answer
Freight indexes measure physical activity in goods movement: tonnage shipped, number of shipments, ton-miles, expenditure on freight services. The Cass Freight Index, the BTS Transportation Services Index, and the Dow Jones Transportation Average (a stock index, not freight volume) are the most cited.
Freight typically precedes the rest of the goods cycle: producers ship before consumers buy, retailers restock before sales rise, and importers schedule containers months ahead of expected demand. When freight volumes contract, the goods economy is usually softening.
The complication: services represent roughly 70% of US GDP. A freight index can be in clear contraction while a services-dominated economy continues to expand — exactly what happened during 2022-2024.
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What the data shows
The Cass Freight Index uses January 1990 as base 1.00. The BTS Transportation Services Index covers all freight modes weighted by economic value added.
Documented characteristics (Cass Information Systems, BTS, FRED, 1990-2026):
- The Cass Freight Index processes around 35 million invoices annually representing roughly 37 billion USD in freight spend.
- Cass historical peak was 1.347 in June 2006; trough was 0.851 in January 2009.
- Manufacturing represents around 11% of US GDP today, while services represent roughly 70%.
- Freight tracks goods consumption, which has been less volatile than services in recent expansions.
The exception that nuances the picture: ACT Research forecasts of the Cass Truckload Linehaul Index were 98.8% accurate on average from 18 months out for 2024 — suggesting freight cycles remain forecastable even when their macro representativeness weakens.
→ Dataset: ISM Manufacturing PMI
Why it happens — the macro mechanism
Freight indexes contain real-economy information that cannot easily be massaged or revised: a truck either rolled or it did not. Three channels explain why they matter — and why they matter less than they used to.
Channel 1 — freight precedes goods consumption. Producers ship to wholesalers, who ship to retailers, who sell to consumers. Each stage adds days to weeks of lead. Freight volume contractions therefore typically precede retail sales weakness by one to three months.
Channel 2 — freight integrates inventory positioning. When firms over-build inventory (as in 2021-2022 supply chain whip), subsequent freight volumes collapse during the destocking phase, even if final demand stays steady. The angle worth flagging: this means freight indexes can signal recession when the underlying economy is merely normalizing inventory positions — exactly the 2022-2023 dynamic.
Freight indexes are also vulnerable to mode-shift: when air freight loses share to ocean, or trucking loses share to rail, an index focused on one mode can mislead.
Channel 3 — freight responds to global trade flows. Container shipping rates and tonnage reflect international trade. Trade tensions, tariff regimes, or geopolitical disruptions flow through freight before they show up in GDP statistics.
Synthesis by regime: in the pre-2000 industrial regime, freight tracked GDP closely because goods were the dominant share of activity; during 2000-2019, the rise of services and globalization weakened the link but freight remained directionally informative; in the post-2020 regime, freight indexes signaled severe recession during the 2022-2023 destocking cycle while services-led GDP grew at a 2-3% pace, illustrating that freight has become a reliable indicator of the goods cycle but a misleading one for the broader economy.
Freight indexes still tell the truth about the goods economy — but the goods economy is now a minority shareholder in the activity that determines whether GDP expands or contracts.
→ Framework: Economic cycle phases
What it means for different economic actors
Industrial firms and retailers use freight data for inventory and capacity planning. The Cass index is widely subscribed by logistics professionals as a real-time read on goods activity.
Investors in transportation stocks (rail, trucking, freight forwarders) read freight indexes as a leading indicator of revenue trends. The Dow Transportation Average can diverge sharply from broad equity indices during inventory cycles.
Macro forecasters increasingly cross-validate freight signals with services PMIs and consumer spending data, recognizing that freight alone now carries information about a shrinking share of GDP.
A common error is to extrapolate freight weakness directly to GDP recession. The 2022-2023 freight collapse coincided with positive GDP growth precisely because the goods sector and the services sector behaved differently.
Practical observation
What the data suggests for understanding your situation:
- Question to ask yourself: Am I reading freight data as a signal about the goods economy specifically, or am I extrapolating it to the whole economy?
- Data to monitor: Six-month rate of change in the Cass shipments index combined with changes in retail inventory-to-sales ratios — the second helps separate genuine demand weakness from destocking.
- Historical parallel: The 2008-2009 recession produced a Cass index drop from 1.34 to 0.85 (-37%), tracking the broader economic collapse; the 2022-2023 freight downturn was nearly as deep but coincided with GDP expansion.
- What the literature documents: Bureau of Transportation Statistics technical brief comparing TSI, Cass and Dow Transportation methodologies; ACT Research freight forecast accuracy reports.
This is descriptive information to help you frame your own analysis. Eco3min does not provide investment advice.
Go deeper
📊 Full study: Yield curve inversion history
📁 Datasets: ISM Manufacturing PMI · US Industrial Production
📖 Related analysis: Baltic Dry Index explained
Related questions
Frequently asked questions
How does the Cass Freight Index differ from the Dow Transportation Average?
The Cass index measures actual physical freight volumes processed through Cass Information Systems’ invoicing platform — a direct read on goods movement. The Dow Transportation Average is a stock index of 20 transportation companies and reflects investor expectations about future earnings, not current freight volume. Both can move in similar directions but for different reasons.
What is the Transportation Services Index from BTS?
The TSI is published by the US Bureau of Transportation Statistics and aggregates freight and passenger services across all modes (truck, rail, water, air, pipeline, transit). It is weighted by economic value added, making it more comparable to GDP components than the Cass index, which is weighted by Cass clients’ shipping patterns.
Are freight indexes useful for non-US economies?
Yes — China’s National Bureau of Statistics publishes freight indices, and the eurozone tracks transportation services in its industrial production statistics. The Baltic Dry Index covers global dry bulk shipping. The methodology and coverage differ across regions, but the underlying logic — physical activity precedes financial settlement — applies broadly.
Last updated — 15 May 2026
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