Where Fleet Fuel Savings Actually Come From

Fuel is usually the second largest controllable cost in a commercial fleet after people, and the one where measurement most reliably produces improvement. It is also the area where the most extravagant claims get made, so it is worth being precise about where the savings actually originate.

The scale is not in doubt. Road transport accounts for 71.7% of all the energy the UK transport sector consumes, on the Department for Energy Security and Net Zero’s most recent figures. A few percent off a fleet’s consumption is worth having.

There are four sources. They are not equal, and they do not add up the way suppliers sometimes imply.

1. Idling

An engine running while the vehicle is stationary and doing nothing productive burns fuel, generates emissions, adds engine hours and wears components. In many operations it is the single largest recoverable loss, and almost nobody knows how much of it they have until they measure it.

No UK body publishes a national idling figure, which is part of the problem: the only number that matters is your own, and you cannot have it until the measurement is running.

The reasons are usually rational from the driver’s point of view: keeping the cab warm or cool, running auxiliary equipment, a habit formed on older vehicles that were harder to restart, or simply not registering that eleven minutes has passed.

Which is why the effective intervention is rarely “stop idling”. It is understanding why each pocket of idling exists and removing the reason — a cab heater that runs independently, a scheduling change that removes the wait, or simply showing a driver their own figure next to the depot average.

One distinction matters more than any other here. On vehicles with auxiliary equipment — tippers, cranes, mixers, refuse compactors, refrigeration — some stationary running is productive. A system that cannot distinguish power take-off engagement from idling will report a working crane as waste, the driver will point this out, and the credibility of every other report will suffer. Get this configured correctly before you show anyone a report.

2. Driving style

Harsh acceleration, late heavy braking and high sustained speeds all cost fuel. The physics is unarguable: energy put into a vehicle and then converted to heat in the brake discs was fuel you paid for.

The saving comes from anticipation — reading further ahead, easing off earlier, arriving at junctions already slow. It also reduces brake, tire and clutch wear, which appears in a different budget line and is frequently overlooked in the business case.

The measurable version of this is where the coaching sits, and where the largest sustained gains are found. It is also where the observer effect is strongest, which brings us to the caveat further down.

3. Speed

Fuel consumption rises steeply above a certain speed, particularly for vehicles with a large frontal area. The difference between a fleet cruising at the limit and one cruising slightly below it is significant across a year of motorway miles, and it costs almost nothing in journey time on realistic routes.

This is often the easiest conversation to have with drivers, because the time penalty is genuinely small and easily demonstrated using their own journey data.

4. Miles not driven

The largest and least discussed source. Fuel not burned because the journey did not happen.

Unnecessary journeys, poorly sequenced routes, empty running, two vehicles covering overlapping areas, jobs that could have been combined, return trips caused by something forgotten, and private mileage on business fuel. This is scheduling and planning rather than driving, and it is where operations with no previous visibility usually find the biggest single number.

Empty running alone is measurable nationally, and it is substantial. The Department for Transport records GB-registered heavy goods vehicles travelling 5,897 million kilometers empty in 2025 — 31% of the 18,975 million vehicle kilometers they covered, and essentially unchanged from 30% the year before. That is a national figure rather than yours, but it is the right order of magnitude for how much commercial running carries nothing at all.

What not to do with the arithmetic

Do not model each of these separately and add them together. They overlap substantially — smoother driving reduces speeding, better routing reduces idling in traffic, and a driver improving on one measure usually improves on all of them.

The four sources are real. Added together they describe a saving almost no fleet achieves, because they overlap.

Apply one conservative percentage to your total annual spend. It will be lower than the sum of the parts and considerably more likely to be achieved. The method for turning that into a defensible business case is set out in the guide to building a telematics business case.

The honest caveat: it fades

The first three months usually show a strong improvement, and a meaningful part of it is the observer effect — people drive differently when they know it is being measured.

That effect decays. Within a year, a fleet that installed telematics and did nothing else typically finds consumption has drifted back toward where it started.

What holds the saving is a rhythm: regular review, individual conversations, visible comparison between depots or teams, and recognition of the drivers who consistently perform well. It does not need to be elaborate. It does need to be consistent, and it needs someone whose job it is.

This is the difference between a fuel saving and a fuel reduction program. The technology delivers the first for a few months. Only the second lasts. Whether drivers accept the program at all is its own subject, and it decides more outcomes than the hardware does — there is more on that in how the platform presents driver data.

A note on electrification

For battery-electric vehicles the mechanisms shift but do not disappear. Idling largely vanishes as a cost. Driving style matters more, not less, because regenerative braking means anticipation directly recovers energy. Speed matters more, because aerodynamic losses dominate at motorway speeds and directly reduce range.

And a new question appears that has no diesel equivalent: is the vehicle charging at the cheapest time and place available? For fleets charging at depot on a time-of-use tariff, scheduling charging correctly can be worth more than driving improvements.

If any of the terminology here is unfamiliar, it is defined a line at a time in the telematics glossary.

Sources: Department for Transport — Domestic road freight statistics, United Kingdom: 2025, published 27 May 2026 (GB-registered HGVs travelled 5,897 million kilometers empty in 2025, 31% of 18,975 million total vehicle kilometers; 30% in 2024). Department for Energy Security and Net Zero — Energy Consumption in the UK 2025, published 20 April 2026, covering 2024 (road transport is the largest contributor to transport energy consumption at 71.7%).