Iwaida Taxi — Japan
Three LPG taxis at Iwaida Taxi were compared against a reference consumption figure. The two Toyota Crown Comfort returned +8.2% and +13.2%; the Toyota Prius α returned +20.8%. The median is +13.2%. The hybrid producing the biggest number is a pattern we see repeatedly — and one we treat as a measurement question, not as a finding.
Hybrids keep producing our largest percentages. That is a reason to look harder at how hybrids are measured, not a reason to advertise the number.
| Operator | Iwaida Taxi (岩井田タクシー), Japan |
|---|---|
| Vehicles | 3 LPG taxis — 2 Toyota Crown Comfort, 1 Toyota Prius α |
| Method | 基準燃費と比較 — comparison against a reference consumption figure |
| Conventional taxis | 5.61 → 6.07 (+8.2%); 6.23 → 7.05 (+13.2%) |
| Hybrid | 13.30 → 16.06 (+20.8%) |
| Result | Median +13.2%, range +8.2% to +20.8% |
| Control group | None |
Every measurement, not just the best one
| Vehicle | Before | After | Change |
|---|---|---|---|
| Toyota Crown Comfort (1) | 5.61 | 6.07 | +8.2% |
| Toyota Crown Comfort (2) | 6.23 | 7.05 | +13.2% |
| Toyota Priusα | 13.30 | 16.06 | +20.8% |
| Median across all 3 measurements | +13.2% |
Method before result
All three vehicles were compared against a reference consumption figure rather than a measured pre-treatment period — the method the dataset records as 基準燃費と比較.
The two conventional Crown Comfort taxis produced +8.2% and +13.2%, consistent with the other conventional LPG taxis in the dataset. The Prius α produced +20.8%, and its baseline (13.30) is more than twice that of the conventional cars, as you would expect from a hybrid.
Across our records, the hybrids consistently return our largest percentages — this Prius α here, and the Prius at Chuo Taxi with an interval reading of over 43%. We consider that a warning sign rather than a selling point. In a hybrid, the share of a journey covered by electric assist varies with traffic, battery state, ambient temperature and driving style, and none of those is recorded in any of these datasets. A change in that share alone would move the fuel figure without the engine behaving differently at all.
Every percentage on this page was recalculated by us from the recorded before-and-after figures rather than taken from the summary column of the source; all of them reproduce the recorded value. That is a check on transcription, not on the measurement itself — it confirms the arithmetic is right, not that the reading was.
The limits of this trial
We publish these next to the result rather than in a footnote. If a limitation would change how you read the number, you should read it at the same time as the number.
Known limitations
- Three vehicles, one operator, no control group, no recorded measurement period.
- The hybrid measurement is not comparable with the conventional ones. Without data on the electric assist share, a hybrid fuel-efficiency comparison cannot isolate a combustion effect.
- The reference consumption figures are not documented — we do not know how they were established for any of the three vehicles.
- The unit behind the LPG figures is unresolved. The dataset labels these columns km/L, but its own CO₂ calculation uses an emission factor of 3.00 kg per kilogram of LPG, which only makes sense if the figures are kilometres per kilogram. The percentage change is unaffected either way — it is a ratio — but we flag it rather than quietly picking one.
- This is a dataset entry, not a trial report. What we hold is the before-and-after fuel-efficiency figure per vehicle as recorded in the master test dataset — not the operator’s raw fuel logs, not the odometer readings behind them, and not a written test protocol.
- There is no control group. No comparable untreated vehicle was tracked over the same period, so seasonal, route and traffic effects cannot be separated from the treatment.
- The measurement dates and the length of each measurement period are not recorded in these entries. We therefore cannot say how far each vehicle ran between the two readings, or which months the comparison covers.
- The figures were recorded by the operator or by the local distributor, not by an independent party, and we cannot re-derive them from primary records.
Reading this evidence in context
The usable signal here is the pair of conventional taxis at +8.2% and +13.2% — modest figures, in line with the other LPG taxi operators in this dataset.
The +20.8% on the hybrid is real as a recorded number and weak as evidence. We publish it in its own row rather than folding it into an average that would flatter the operator group.
For a taxi fleet considering a pilot, the practical consequence is a design point: treat conventional and hybrid vehicles as separate groups, and expect the hybrid figures to be noisier.
Questions operators ask about this trial
Why treat the hybrid result with suspicion?
Are these figures consistent with your other taxi data?
Is three vehicles enough for a page?
Provenance
- Source
- Eco-Spray / NanoEFX master test dataset, compiled 22 March 2020 — operator-named section
- Recalculation
- All percentages recomputed from the recorded before-and-after figures
- Raw records
- Held by the operator or the local distributor — not in our possession
- Operator entry
- 岩井田タクシー — Iwaida Taxi
- Method as recorded
- 基準燃費と比較 (against reference consumption)
- Name release
- Operator naming approved by ECO EFX Solutions, 15 August 2026
- Last checked
- 15 August 2026
The only baseline that matters is yours
Every trial on this site was run on someone else’s vehicles, duty cycle and baseline. A NanoEFX pilot measures yours — and we will help you design it with a control group so the result stands up.