Rail and Truck Volumes Both Rose 4.4%: Measure Modal Substitution Lane by Lane

Freight markets rarely move in a clean, winner-takes-all direction. The latest evidence is unusually symmetrical: FreightWaves reported that its Truckload Volume Index and loaded rail container volume each increased exactly 4.4% over the most recent three-month period. The rail index also reached its second-highest level since 2008.

Those numbers support a stronger industrial freight environment, but they do not prove that truck and rail are gaining equally on every corridor. Nor do they disprove modal conversion. National aggregates can rise together while individual shipper lanes move sharply from highway to intermodal—or back again.

The useful question is not, “Is rail winning?” It is, “Which shipments on which lanes should change modes under today’s operating conditions?”

Matching growth rates can hide substitution

The FreightWaves analysis of rail and truck volumes found the same 4.4% three-month growth rate for both modes. That near-perfect match can occur even when substitution is active because the underlying freight base is changing.

Suppose total demand rises on a long-haul corridor. Rail could capture a larger share of replenishment freight while trucks handle more expedited orders, shorter hauls, and freight outside practical ramp pairs. Both modes record growth, but their shipment mix changes materially. An aggregate index will not show that allocation decision.

Timing creates another blind spot. Intermodal shipments generally move more slowly than direct truckload. Freight tendered to rail in late summer may reduce truck demand later in the season, when those goods would otherwise require expedited replenishment. The immediate data can therefore show healthy demand in both modes even as rail conversion suppresses future highway tenders.

Planners need origin-destination detail, shipment attributes, and promised-delivery performance—not a national scorecard.

Compare the full door-to-door economics

Linehaul price is important, but it is only one component of modal cost. Inbound Logistics reports that intermodal tends to cost about 8% to 18% less than over-the-road trucking. That is a meaningful starting advantage, particularly on repeatable long-distance lanes. It is not automatically a net saving.

A defensible comparison should include:

• Origin drayage, destination drayage, fuel surcharges, and accessorial exposure
• Rail ramp cutoffs, terminal dwell, appointment constraints, and storage risk
• Expected transit time and the variability around that average
• Inventory carrying cost during the additional time in transit
• Stockout, production interruption, or missed-delivery penalties
• Damage risk, cargo value, handling sensitivity, and claims history

The inventory calculation is often neglected. A slower move keeps working capital tied up longer. For a low-value, predictable shipment, that cost may be trivial relative to the linehaul saving. For high-value components feeding a production line, one additional day plus variable dwell can erase the entire transportation benefit.

Service variability matters more than the average. A lane averaging four days with a narrow range may be operationally safer than one averaging three days but frequently taking six. Measure the 90th- or 95th-percentile door-to-door transit time and price the buffer inventory needed to protect the customer promise.

Build a modal-substitution score

A practical score can rank eligible shipments without pretending every factor shares the same unit. Normalize each factor from 0 to 100 and weight it according to business priorities:

Modal substitution score = 30% net cost advantage + 25% service fit + 15% volume consistency + 15% inventory tolerance + 10% emissions benefit + 5% operational fit.

Net cost advantage should use expected total landed transportation cost, including drayage and accessorials. Service fit should measure whether the intermodal lane’s percentile transit time stays inside the required delivery window. Volume consistency rewards regular, forecastable flows that can fill containers and support scheduled tendering.

Inventory tolerance incorporates product value, days of supply, buffer stock, and the consequence of lateness. Operational fit covers ramp distance, loading capability, container availability, appointment rules, and whether the receiving location can absorb schedule variation.

Emissions deserve explicit treatment rather than a footnote. Inbound Logistics cites average greenhouse-gas reductions of up to 75% when freight moves by rail instead of truck. The precise saving varies with dray miles, route, equipment, load factor, and rail performance, so calculate it lane by lane. Still, the magnitude can materially affect shipper sustainability targets and customer reporting.

A score above an agreed threshold can trigger an intermodal quote or controlled pilot. A middle band should route to analyst review. A low score keeps the shipment on truckload. The thresholds should reflect the company’s risk appetite rather than a universal benchmark.

Make the score dynamic

Modal decisions decay quickly when they live in an annual bid spreadsheet. Rates change. Ramp dwell expands. Fuel moves. Delivery windows tighten. New facilities alter dray distance. Each change can flip the economics of a lane.

Refresh the score whenever a contract rate changes, a rolling service metric crosses tolerance, a delivery requirement is revised, or a shipment profile shifts. Weekly updates suit active high-volume corridors; monthly reviews may be sufficient for stable lanes. Preserve the inputs and decision so planners can explain why a shipment changed modes.

Pilots should compare matched freight over several cycles. Track door-to-door cost, median and percentile transit, tender acceptance, claims, carbon output, and inventory exceptions. If rail misses the service threshold, diagnose whether the problem is structural or temporary before reverting the entire lane.

The identical 4.4% growth rates are a reminder that broad market indicators provide context, not routing instructions. Real modal advantage is created shipment by shipment, where cost, time, reliability, inventory, and emissions meet an actual customer commitment.

Want to turn lane-level freight data into repeatable routing decisions? Request a CXTMS demo to see how centralized rates, shipment history, and execution workflows can support smarter modal planning.