Seasons and Weather

Fleet figures vary with the weather more than most reporting allows, and the variation is large enough to invert a comparison.

What moves with temperature

Diesel consumption rises in cold weather, from warm-up, from denser air and from heater load.

Electric range falls sharply, by a quarter or more at low temperatures, which is the operational constraint rather than a cost one.

Battery failures cluster in the first cold snap, which is predictable and preventable.

Tyre pressure falls with temperature, which raises consumption and is the commonest winter fault.

What moves with the work

Peak periods change round composition: more drops, more stop-start, worse consumption per mile.

Which means a seasonal consumption rise is partly weather and partly work, and separating the two requires knowing the round.

Compare the same round across years rather than across months, which is the only comparison that means anything.

The planning consequences

Do not set annual targets from a summer quarter.

Do not judge a new vehicle type introduced in October against a fleet baseline from July.

And do not plan electric rounds on average range, which is covered in its own note and is worth repeating because it is the failure that strands vehicles.

Preventive work that pays

Battery testing before winter, which telematics supports directly: cranking voltage is readable and a weak battery is visible before it fails.

Tyre pressure checks at the temperature change.

Coolant and screenwash specification, which is trivial and produces vehicles off the road when neglected.

Schedule these as a seasonal task rather than waiting for the failures, because the failures arrive in the same fortnight across the fleet.

Reporting around it

Year-on-year, same period, for anything seasonal.

Rolling twelve months for trend.

Never month against previous month for consumption, which produces conclusions about management from a change in the weather.

The measure

Consumption by vehicle type, same month year on year.

Cold-start failures per winter, which should fall if the preventive work happens.

And electric range achieved against planned, by month, which tells you whether the round assignments hold through the year.

Compare year on year, same period

Never month against previous month.

Consumption, range and failures all move with the weather by more than most management changes do.

A month-on-month comparison produces conclusions about management from a change in temperature.

Rolling twelve months for trend, same month year on year for level.

Turn the boundary into a test

For a concrete product reference, this seasonal-work reference can help turn this boundary into a test. Verify the current behaviour with representative fields and record what reaches the destination.