A BRIDGE FALLS. A PORT SLOWS. WHO FEELS IT NEXT?
In the early morning of March 26, 2024, the cargo ship Dali struck Baltimore's Francis Scott Key Bridge, sending it collapsing into the Patapsco River. Six construction workers were killed, vessel traffic ground to a halt, and one of the country's most important port gateways suddenly became the center of a national supply-chain story.
But for an economist, the mystery does not end at the bridge. The Port of Baltimore was never just moving cargo. In 2023 it handled 52.3 million tons of foreign cargo worth roughly $80 billion, including major flows of automobiles, roll-on/roll-off machinery, imported sugar, and imported gypsum. So the real question is not what happened at the port? It is who was waiting for what the port helped move?
That is the forward-linkage question, and it changes how the whole story reads. A transportation disruption can become a construction problem. A port delay can become a food manufacturing problem. A warehousing bottleneck can become a retail problem. A trucking shock can ripple into real estate, hospitals, or manufacturing. The shock does not simply sit at the scene of the accident—it travels.
And when a shock travels, IMPLAN calls in Sherwood "Link" Holmes.
What Will I Learn in This Article About Forward Linkages in IMPLAN?
- How forward linkages work — discover the mechanics of forward linkages and how they differ from traditional backward-facing impact analysis in IMPLAN.
- Why supply chain disruptions don't stay local — explore how upstream shocks travel downstream through the economy, creating ripple effects across interconnected industries and sectors.
- How to model cost-push scenarios in IMPLAN — master the techniques for revealing hidden sectoral pressure points and quantifying the downstream economic consequences of supply-side changes.
ELEMENTARY, MY DEAR IMPLAN
A shock has struck the economy. The usual suspects have been questioned, the direct effect identified, the upstream suppliers' statements taken. The backward linkages have been checked, double-checked, and entered into evidence. And yet something is still missing.
Somewhere downstream, industries are absorbing costs, losing capacity, adjusting operations, or discovering that an output they barely think about has suddenly become harder to afford. The shock did not vanish. It moved. That is when IMPLAN calls in Sherwood "Link" Holmes—Sherlock's long-lost American relative, and the only consulting detective trained to follow an output after it leaves the scene.
His motto is simple: backward linkages ask who helped make the output; forward linkages ask who was waiting for it.
Welcome to The Downstream Detective.
THE FORWARD-FOCUSED MAGNIFYING GLASS
What is the difference between forward linkages and backward linkages?
Most economic impact analysis begins with a familiar question: if demand increases for this industry, what happens upstream? If households buy more cars, what happens to steel, glass, rubber, labor, parts manufacturing, transportation, professional services, and energy? That is a backward-linkage story—we begin with demand and trace what production requires.
But some shocks do not begin with demand. Sometimes a key input becomes more expensive, a production service becomes constrained, a port slows, a warehouse fills, freight costs rise, or a material gets harder to access. In those cases, the detective has to turn around and ask a different set of questions: Who uses this output to keep producing? Where does the cost pressure go next? Which industries were quietly depending on this commodity, service, or production channel?
This is the inside-out view of the economy. Instead of standing outside an industry and asking what it buys, we step inside the output itself and ask where it travels. The clue is not always where the shock begins—it is who needed the thing that got shocked.
THE CASES: MARYLAND AND THE PORT OF BALTIMORE
For this investigation, the scene is Maryland, and that choice matters. The Port of Baltimore is not just a port; it is a gateway for multiple downstream dependency trails at once—vehicles, heavy machinery, sugar, gypsum, freight, warehousing, trucking, construction materials, and distribution services. In detective terms, Baltimore gives Sherwood a crowded crime scene, with not one trail of evidence but many.
A transportation disruption may become a construction issue. A warehousing cost increase may become a retail issue. A gypsum shock may become a housing and facilities issue. A sugar shock may become a bakery, beverage, and confectionery issue. A wholesale shock may become an auto repair and vehicle manufacturing issue. That is what makes Maryland such a useful place to teach forward linkages: the downstream story is not abstract here. It is visible.
EACH CASE IS A SHOCK
The Downstream Detective casebook uses IMPLAN's Forward Linkage tools to examine a series of cost-push and contribution scenarios. For the price shocks, we use the Price Change / Cost-Push Guide: each case selects a commodity, applies a price increase, and traces which industries face higher annual costs because they use that commodity directly or indirectly. For the final reveal, we switch to the Downstream Industry Contribution Guide, which asks not what happens when a commodity gets more expensive, but what downstream economic activity is tied to a reduction in a source industry's production.
In short, Price Change / Cost-Push asks what happens when the output becomes more expensive? while Downstream Industry Contribution asks what activity was this industry holding up? Sherwood never confuses the two—a good detective never mixes up the weapon.
CASE FILE 1: THE COSTLY CARRIAGE
The first case begins with Truck transportation services (IMPLAN Commodity 3399) and a 25% price increase.
At first glance the outcome seems obvious: trucking gets more expensive, so transportation absorbs the hit. But forward linkages reveal something more interesting—the shock does not stay on the road. The total annual cost increase comes to $1.39 billion, with $623.6 million falling directly on industries and another $150.8 million arriving indirectly.
The top downstream suspects:
- Truck transportation — $40.6 million
- Construction of other new residential structures — $31.1 million
- Construction of new single-family residential structures — $24.8 million
- Construction of new commercial structures, including farm structures — $22.8 million
- Other real estate — $18.1 million
🔍 Sherwood's Reveal
The truck was not merely moving goods. It was carrying construction schedules, real estate activity, and production timing. The road did not vanish—it simply became more expensive to depend on.
CASE FILE 2: THE HARBOR TOLL
The second case turns to Water transportation services (IMPLAN Commodity 3398), again with a 25% price increase.
Compared with trucking, this case leaves a very different fingerprint. The total annual cost increase is $275.2 million, with $30.2 million landing directly on industries and $8.1 million indirectly.
The top downstream suspects:
- Scientific research and development services — $11.9 million
- Postal service — $3.3 million
- Construction of new highways and streets — $1.0 million
- Construction of other new residential structures — $951,091
- Wet corn milling — $892,620
- Other real estate — $783,525
What makes this case instructive is the contrast: trucking produced a broad domestic cost burden, while water transportation produced a smaller, more specialized downstream pattern. Not every transportation shock spreads the same way.
🔍 Sherwood's Reveal
Do not stare only at the dock. The evidence is in the firms waiting for what the dock was meant to move. The harbor was not silent—its trail was simply more selective.
CASE FILE 3: THE WAREHOUSE WITH NO ROOM
The third case selects Warehousing and storage services (IMPLAN Commodity 3404), with a 25% price increase.
This is where the casebook starts to feel especially intuitive, because warehousing is not just a room full of goods—it is the management of timing, inventory, delay, and flow. When it gets more expensive, the total annual cost increase reaches $795.3 million, with $572.5 million falling directly on industries and $236.6 million indirectly.
The top downstream suspects:
- Retail – Food and beverage stores — $40.3 million
- Employment services — $38.7 million
- Warehousing and storage — $35.9 million
- Retail – Motor vehicle and parts dealers — $34.3 million
- Truck transportation — $29.9 million
🔍 Sherwood's Reveal
A warehouse is not a room. It is time made physical. This shock shows how much of the economy depends not only on producing goods, but on holding them, sequencing them, and making them available at the right moment. When waiting becomes expensive, the bill appears downstream.
CASE FILE 4: THE GYPSUM AFFAIR
The fourth case selects Gypsum products (IMPLAN Commodity 3201), with a 20% price increase.
This is a beautifully focused forward-linkage case. Gypsum is not flashy and rarely makes headlines, but it sits quietly inside construction, facilities, repair, and building activity. The total annual cost increase is $104.6 million, with $40.6 million falling directly on industries and $8.3 million indirectly.
The top downstream suspects:
- Construction of other new residential structures — $6.5 million
- Facilities support services — $6.0 million
- Construction of new single-family residential structures — $5.7 million
- Maintenance and repair construction of nonresidential structures — $3.8 million
🔍 Sherwood's Reveal
The clue was not in the bridge. It was in the wallboard. A gypsum shock becomes a construction shock because construction was waiting for the material—and that is precisely the point of forward linkages: they show how a narrow input can become a sectoral pressure point.
CASE FILE 5: THE SWEET TOOTH CAPER
The fifth case selects Sugar cane (IMPLAN Commodity 3068), with a 20% price increase.
Here the trail is sticky. The total annual cost increase is $178.3 million, with $19.4 million falling directly on industries and $1.6 million indirectly.
The top downstream suspects:
- Sugar cane mills and refining — $11.1 million
- Bread and bakery product manufacturing — $2.2 million
- Spice and extract manufacturing — $1.2 million
- Bottled and canned soft drinks and water — $1.2 million
- Chocolate and confectionery manufacturing — $628,594
🔍 Sherwood's Reveal
The trail was sticky, Watson. Naturally, it led to sugar. This case shows that forward linkages do not always reveal massive economy-wide disruption; sometimes they reveal a narrow, recognizable ingredient chain. Sugar moves through refining, bakeries, beverages, spices, and confectionery, and the shock becomes visible wherever sweetness enters production.
CASE FILE 6: THE AUTOMOBILE THAT NEVER ARRIVED
The sixth case selects Wholesale services, motor vehicle and motor vehicle parts and supplies (IMPLAN Commodity 3375), with a 20% price increase. This case is about distribution as hidden infrastructure.
The total annual cost increase is $617.0 million, with $205.1 million falling directly on industries and $62.6 million indirectly.
The top downstream suspects:
- Automotive repair and maintenance, except car washes — $28.4 million
- Automobile and light duty motor vehicle manufacturing — $17.9 million
- Landscape and horticultural services — $11.7 million
- Truck transportation — $11.4 million
- Other real estate — $9.5 million
- Other engine equipment manufacturing — $7.1 million
🔍 Sherwood's Reveal
The clue was not under the hood. It was in the wholesale network. The automobile never arrived because the distribution channel became more expensive before the vehicle ever reached the lot. Wholesale services may look like a middle layer, but forward linkages show that middle layers often hold the economy together.
THE BIG REVEAL: WHAT WAS TRUCK TRANSPORTATION HOLDING UP?
The final case is different.
The first six used commodity price shocks, but the Big Reveal uses the Downstream Industry Contribution Guide with Industry 399: Truck transportation. This time Sherwood does not ask what happens when trucking becomes more expensive.
He asks something sharper: what downstream economic activity disappears when truck transportation production is reduced?
To answer that, we modeled a negative production value of -$556,248,214 for Maryland truck transportation. That number traces back to the Costly Carriage case, where a 25% price increase produced a total annual cost increase of $1,390,620,534. If that figure represents 25% of the underlying truck transportation service value, the implied annual base is:
$1,390,620,534 ÷ 0.25 = $5,562,482,136
From there, we modeled roughly 10% of that base:
$5,562,482,136 × 0.10 = $556,248,214
In plain English, the Big Reveal models an approximate 10% reduction in Maryland truck transportation production – a scenario that allows us to remove $556.2 million of truck transportation from the scene and observe the downstream ripples.
The results are dramatic. A -$556.2 million production shock to Maryland truck transportation is associated with -$910.0 million in output, -3,991 jobs, -$311.2 million in labor income, -$437.5 million in contribution to GDP, and -$93.9 million in tax revenue. By effect type, the direct portion accounts for -2,695 jobs and -$584.8 million in output, the indirect portion for -1,296 jobs and -$325.2 million in output, and the induced portion for nothing at all.
That zero matters. In a Forward Linkage contribution case, the model is not telling a household-spending story; it is tracing downstream production dependence. The earlier cases showed where costs rose. The Big Reveal shows what truck transportation was holding up.
🔍 Sherwood's Final Reveal
The trucks were not just moving goods. They were moving economic possibilities. The shock was never missing—it was hiding in the industries that depended on truck transportation to keep producing.
READING THE CLUES
The casebook teaches three lessons.
First, each shock has a different fingerprint. Trucking spreads broadly across construction and real estate. Warehousing hits retail, staffing, trucking, and inventory-heavy sectors. Water transportation is more specialized, gypsum is construction-focused, sugar follows a food-production trail, and wholesale services reveal the hidden importance of distribution networks.
Second, large dollar effects and high exposure are not the same thing. A large dollar effect shows scale, where the biggest downstream cost appears in absolute terms. Exposure shows vulnerability, where the shock matters most relative to the size of the affected industry. A good detective looks at both.
Third, forward linkages change the question. Backward linkages ask who helped make it? Forward linkages ask who needed it next? That question matters for ports, tariffs, logistics disruptions, commodity shortages, industrial bottlenecks, construction materials, energy, food systems, and any scenario where a cost or supply shock moves forward through the economy.
NO INDUCED EFFECTS, NO PROBLEM
One thing users will notice in Forward Linkage results is that induced effects do not appear the way they do in standard demand-driven impact analysis. That is not a mistake. Forward linkage analysis is not primarily asking how household spending changes after labor income shifts; it is asking how cost, price, or production pressure moves through the industries that use an output.
The vocabulary shifts accordingly. In a backward model, indirect effects usually refer to suppliers. In a forward model, indirect effects are part of the downstream purchaser trail. That is why Sherwood keeps repeating: we are not following who supplied the victim—we are following who depended on the victim.
CASE CLOSED
The Downstream Detective turns Forward Linkages into a mystery worth solving. A price increase is not just a number, a commodity is not just an input, a warehouse is not just a room, a truck is not just a vehicle, a port is not just a dock, and a wholesale network is not just a middleman. Each one is a clue.
Forward Linkages help us see that an industry's importance is not only what it buys, not only who it employs, and not only what it sells—it is also what becomes possible because its output exists. Backward linkages show what production requires; forward linkages show what production enables.
Elementary, my dear IMPLAN: the shock was downstream all along.
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Written July 2, 2026