Empty Running and Backhaul
Roughly three in ten of the kilometres driven by heavy goods vehicles in the UK are driven with nothing in the back. The lorry is on the road, the engine is burning diesel, the driver is being paid — and it is carrying air. Every one of those kilometres emits carbon while moving no freight at all.
That waste has a name, and so does the fix. Empty running is a freight vehicle travelling with no load; backhaul is putting freight on the return leg so it does not — and because an empty vehicle still burns fuel for zero cargo, cutting empty running is one of the biggest levers on freight carbon per tonne-kilometre.
Empty running (deadheading) is a freight vehicle moving unladen; backhaul is securing a load for the return so it is not empty. Around 30% of UK HGV vehicle-kilometres run empty, and an empty vehicle still burns fuel — raising the effective CO₂e per tonne-kilometre.
What Empty Running and Backhaul Mean
Empty running is the movement of a freight vehicle carrying no payload — an unladen leg. In North American trucking the same thing is called deadheading, and container logistics calls the equivalent movement of empty boxes empty repositioning. The most common cause is simply the return leg of a round trip: a lorry delivers a full load in one direction and then has to get back, often with nothing to carry.
Backhaul is the answer to that. In its literal sense the backhaul is the return leg of a journey; in practice “backhaul”, “backloading” and “backfilling” all mean the same thing — finding freight for that return leg so the vehicle earns its keep in both directions instead of running empty one way. A haulier who consistently backloads is running fuller across the whole round trip, which is exactly what raises the effective load factor and lowers the carbon per tonne carried.
Empty running is the problem — vehicle-kilometres driven unladen, burning fuel for no freight. Backhaul is the fix — loading the return leg so those kilometres carry cargo instead of air. Together they describe how well a vehicle is used across a whole round trip, not just its outbound load.
Why Vehicles Run Empty
Empty running is rarely carelessness; it is usually structural. Three causes dominate:
Directional imbalance
Freight flows are lopsided. Goods pour into cities and out of ports far more than they flow back, so vehicles arrive full and often have nothing to carry on the return. Trade imbalance is the single biggest driver of empty kilometres.
Specialised vehicles
A fuel tanker, a car transporter, a cement mixer or a refrigerated food trailer cannot simply pick up a general return load. Dedicated equipment and contamination or hygiene rules leave many vehicles with no legal or practical backload.
Time and scheduling
A return load has to exist at the right place, at the right time, going the right way. Tight delivery windows, just-in-time schedules and dedicated contracts often leave no slack to divert and collect one.
These structural reasons are why empty running is stubborn — and why reducing it usually means matching flows across many operators, not just trying harder within one.
Why It Matters for Emissions
An empty vehicle is not a zero-emission vehicle. It still burns most of the fuel a part-loaded one would — a litre of diesel emits about 2.58 kg CO₂e [GreenCalculus fuels.gbr.diesel_average_biofuel_blend.litre · DEFRA 2026 'Fuels'!D72 · v2026.284] whether the trailer behind it is full or empty — but it delivers no freight for those emissions. The carbon problem is therefore one of allocation. If you look only at the loaded leg, an empty return seems free; but the round trip is a single operation, and the emissions of the empty leg have to be charged to the goods that were actually moved.
Charged that way, empty running directly inflates the effective emission factor per tonne-kilometre. It is the round-trip expression of load factor: a truck can be 100% loaded outbound and still have a poor whole-journey utilisation if it comes back empty. This is the same mechanism as the empty repositioning of containers in intermodal networks — units travelling empty to where they are next needed — and it is why utilisation must be judged over the complete there-and-back cycle, not one direction.
Empty Running Beyond Road
Although the term is most associated with lorries, empty running is a phenomenon of every freight mode, driven by the same directional imbalance. In container shipping it takes the form of empty container repositioning: because far more full containers flow out of major exporting regions than come back, carriers must ship the empty boxes back to where the next export load waits. A large share of container movements worldwide — commonly put at around one in five — is the repositioning of empties, a substantial cost to the industry and a source of emissions from moving empty steel across oceans and roads.
Rail sees the same thing as empty wagon movements, especially for the specialised bulk wagons used for coal, aggregates or cars, which typically return empty because they cannot carry a general return load — the rail cousin of the specialised-vehicle problem on the road. The accounting logic is identical across all of these: the empty movements are charged to the laden ones, so they raise the effective carbon intensity of the freight that is actually carried. And the remedies rhyme too — better matching of flows, shared or pooled equipment (such as neutral “grey-box” container pools), and network design that chains laden legs together instead of sending units out and back empty.
Backhauling: The Lever
Because the empty leg is already being driven, filling it is unusually efficient: the marginal carbon of adding freight to a trip you are making anyway is small, so backhaul converts near-wasted kilometres into productive, low-marginal-carbon capacity. That makes it one of the highest-leverage moves in freight decarbonisation. The main ways it is done:
| Lever | How it cuts empty running |
|---|---|
| Backloading | Actively selling or booking freight for the return leg of an existing trip |
| Freight exchanges / load matching | Digital marketplaces that pair empty vehicles with loads needing to move the same way |
| Horizontal collaboration | Competing shippers or hauliers sharing capacity so one firm’s outbound is another’s backload |
| Network redesign | Triangular routing and better depot siting so trips chain loaded legs instead of out-and-back |
The ceiling is set by the structural causes above — perfect backloading is impossible when the freight simply is not there, or the vehicle is specialised. But even partial gains matter, because every empty kilometre converted to a loaded one improves the round-trip carbon of freight the operator was already moving.
What makes empty running hard to solve is that it is fundamentally a matching problem, and often a collective one. A single haulier can only backload against the freight it happens to see; the empty leg it cannot fill may be exactly the loaded leg another operator is desperate to move. This is why digital freight exchanges — marketplaces that pool available loads and empty capacity across many firms — and horizontal collaboration between shippers have become central to cutting empty kilometres: they widen the pool of loads any given empty leg can be matched against. The long-term vision, sometimes called the “physical internet”, pushes this further, imagining freight routed through shared, standardised, interconnected networks much as data packets are routed online, so that a vehicle almost always has a next load. Each step in that direction converts empty running into carried freight without adding a single vehicle to the road.
A Worked Example
Take a lorry on a 300 km delivery that must return to base — a 600 km round trip — carrying 20 tonnes outbound. Over the round trip it burns about 180 litres of diesel, so at a frozen 2.58 kg CO₂e per litre the trip emits roughly 464 kg CO₂e. What changes with backhauling is how much freight those emissions are spread across:
| Round trip | Freight moved | Tonne-km | Trip CO₂e | Intensity (kg CO₂e / t·km) |
|---|---|---|---|---|
| Loaded out, empty back | 20 t one way | 6,000 | 464 kg | 0.077 |
| Backhaul (loaded both ways) | 20 t each way | 12,000 | 464 kg | 0.039 |
Backhauling nearly halves the effective carbon per tonne-kilometre — the same fuel, the same trip, but twice the freight delivered. The empty return in the first row is doing nothing but emitting; the second row puts those kilometres to work.
To keep the arithmetic clear this holds fuel constant, but a laden return burns somewhat more diesel than an empty one, so a real backhaul emits a little more in total than the empty-return case — its per-tonne-kilometre figure would sit a touch above 0.039, not exactly half. The saving is still large, because the extra fuel is small next to the doubling of freight. The 2.58 kg CO₂e/litre figure is a frozen snapshot of the live UK diesel factor.
How Empty Running Is Counted
In freight carbon accounting, empty running is captured through the empty running factor — the share of vehicle-kilometres (or of trips) driven unladen. The GLEC Framework treats it as an explicit parameter: you can raise the intensity of a movement to reflect known empty running, or use a default. The published average factors in the DEFRA conversion factors already embed a typical level of empty running for each vehicle type, which is one reason an “average laden” factor is higher than a purely full-load calculation would suggest.
The key modelling choice is the boundary. If you account per consignment on a one-way basis, the empty return may be invisible unless the factor already includes it; if you account per round trip or per vehicle, it appears directly. Best practice — and what tools like the road-freight calculator and the fleet carbon footprint calculator support, following the GLEC road-freight methodology — is to make the empty running explicit so a backhaul improvement actually shows up in the numbers. If it is hidden inside a default factor, the carbon benefit of backloading can never be measured.
Common Confusions
- Thinking an empty leg is emissions-free. An unladen vehicle burns most of the fuel a loaded one does; it just carries nothing for it. Empty kilometres are among the most wasteful in freight.
- Judging utilisation on the loaded leg only. A truck can be full outbound and empty back — its whole-trip load factor is then only about half of what the outbound leg suggests.
- Hiding empty running inside an average factor. If the emission factor already bakes in typical empty running, a real backhaul improvement won’t show unless you model empty running explicitly.
- Assuming all empty running can be removed. Directional imbalance and specialised vehicles set a floor; the goal is to cut avoidable empty kilometres, not to reach zero.
- Confusing backhaul with the outbound trip. Backhaul specifically means loading the return leg; the carbon gain comes from using kilometres that were going to be driven anyway.
Frequently Asked Questions
Empty running is the movement of a freight vehicle that is carrying no payload — an unladen leg of a journey. It is also called deadheading, and the equivalent movement of empty shipping containers is called empty repositioning. The most common cause is the return leg of a round trip: a vehicle delivers a load in one direction and then travels back, frequently with nothing to carry. Around 30% of heavy-goods-vehicle kilometres in the UK are run empty. It matters because an empty vehicle still burns fuel and emits carbon dioxide, so those kilometres are wasted from an emissions point of view — carbon is spent moving no freight.
Backhaul is the return leg of a freight journey, and “backhauling” or “backloading” means finding cargo to carry on that return leg so the vehicle does not run empty. It reduces emissions because the return trip is being driven regardless — so the marginal carbon of adding freight to it is small, while the freight delivered can double. Spreading the round trip’s largely fixed emissions across twice the tonne-kilometres nearly halves the effective carbon per tonne-kilometre. That is why backhauling, along with freight exchanges and collaboration between shippers, is one of the highest-leverage actions in road-freight decarbonisation.
Mostly for structural reasons rather than poor planning. First, freight flows are directional: goods move into cities and out of ports far more than they flow back, so vehicles arrive full and often have no return load. Second, many vehicles are specialised — fuel tankers, car transporters, cement mixers and refrigerated food trailers cannot pick up a general backload because of their equipment or contamination and hygiene rules. Third, timing: a return load has to exist in the right place at the right time going the right way, and tight schedules or dedicated contracts often leave no room to collect one. These structural causes are why cutting empty running usually requires matching flows across many operators, not effort within a single one.
They are closely related but not identical. Load factor measures how full a vehicle is relative to its capacity on a given leg; empty running is the special case of a leg with zero load, usually the return of a round trip. Empty running is really the round-trip expression of load factor: a vehicle can be fully loaded outbound (a high load factor on that leg) yet have poor whole-journey utilisation because it comes back empty. That is why utilisation should be judged over the complete round trip. Reducing empty running through backhauling is one of the main ways to raise the effective load factor across a whole journey.
Through an empty running factor — the share of vehicle-kilometres or trips driven unladen. The GLEC Framework treats it as an explicit parameter you can set from your own data or take as a default, and DEFRA’s published average conversion factors already embed a typical level of empty running for each vehicle type, which is part of why an average-laden factor is higher than a full-load calculation would be. The important modelling choice is the boundary: accounting per round trip or per vehicle makes empty running visible, whereas a one-way per-consignment view can hide it inside the factor. To measure the benefit of backhauling, empty running should be modelled explicitly rather than buried in an average.
Deadheading is the same thing as empty running — it is the term used in North American trucking for a vehicle travelling with no load, typically after a delivery or while repositioning to the next pickup. A “deadhead mile” is an empty mile. The word carries the same emissions meaning: the vehicle is burning fuel and emitting carbon while moving no freight, so deadhead miles are a direct target for reduction through backhauling and better trip planning. In container shipping and rail, the analogous idea is empty repositioning — moving empty units to where they are next required.
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