TTC eBus Errata: Tonnes and Kilos Are Different

In a comment on my article TTC eBus Study: Final Results, an alert reader noted that the claimed GHG reduction from the new fleet was vastly out of proportion. Here is the TTC’s chart from that report and accompanying text (highlighing added).

The TTC’s first 60 eBuses were procured from BYD, NFI and Proterra. Prior to the delivery of these eBuses, three garages (Arrow Rd, Mt Dennis and Eglinton Garages) were retrofitted with depot charging systems to accommodate charging up to 25 eBuses per location. All 60 eBuses procured have now been in-service between one to 2.5 years at the TTC with more than 2.5 million kilometres driven, and have reduced GHG emissions by 3.3 million metric tonnes.

TTC Report at p. 14

The basic problem here is the claim that for every kilometre travelled by an eBus rather than by a diesel bus, the saving would be over 1 Tonne of GHG. In the paragraph above, the saving should be 3.3 thousand metric tonnes, not 3.3 million. Who knows how many times this erroneous number will be cited.

The basic numbers are summarized in one paragraph on page 97 of the report:

GHG Reduction

The greenhouse gases (GHG) reduction is primarily due to the avoidance of diesel fuel consumption. At an average fuel economy of 0.53 l/km, the TTC’s Nova clean diesel buses release 1.4 kg of CO2 per kilometre driven. The generation of electricity also creates emissions through many factors including direct emissions from fuel-fired power plants. For Ontario, the average CO2 emission for base load power is 32 g/kWh. The eBus fleet in 2021 averaged 1.62 kW/km (including all non-operating energy consumption sources), which equates to emissions of 0.05 kg CO2/km. Based on the fleet mileage of 1,555,174 km in 2021, emissions associated with the electricity supply are 80.8 Tons CO2. An equivalent clean diesel bus fleet would have emitted 2,177 Tons of CO2.

Note: The highlighted value should be 1.62 kWh/km. This is a typo in the TTC’s original text.

Running the Numbers

To save readers from working through these numbers, here they are consolidated as a spreadsheet.

The table below compares the TTC’s cited numbers with calculated values. Where a value is calculated, I have not rounded it as in the TTC’s descriptive text. For example, the GHG emissions per km for eBuses is shown as 0.05184 rather than 0.05 kg/km. Cells highlighted in yellow have the wrong units, but this is what the TTC specified in its chart.

The problem here is that the line “GHG Savings” claimed is erroneously stated in Tonnes (1,000 kg) rather than in kilos making the numbers 1,000 times bigger than they actually are.

This has the absurd effect of making the “saving” per kilometre over 1 tonne when the diesel fuel we start with weighs less than 1 kg.

I checked with the TTC, and, yes, the chart is wrong. It should specify savings in kilos, not in tonnes.

The calculated emission savings are obtained by multiplying the “delta” value (difference in emissions by fuel source) by the reported fleet mileages. The claimed values are taken from the TTC’s chart above.

There is a further problem that the ratio of claimed GHG savings to distance operated varies from one vendor to another. There is no explanation for this although the report does cite different fuel consumption rates for each manufacturer’s bus.

Although I have asked, the TTC has not explained why these values are different.

Clean Diesels vs Hybrids as a Reference

There is a further issue with the numbers published by the TTC. They are based on a comparison with “clean diesels” even though some of the vehicles to be replaced include the first generation of hybrids with have lower fuel consumption.

The TTC reports that the GHG saving between a first generation hybrid and an eBus is about 1.315kg CO2/km, as against 1.379 for clean diesels (from the table above). This suggests that the first generation hybrids are not saving much fuel compared to the diesels (less than 5%).

Getting It Right

The main report contains a more reasonable number:

When the entire fleet is zero-emissions, the following benefits are expected to be realized:

1. Greenhouse gas emissions will be reduced by approximately 250,000 tonnes of CO2 annually; […]

TTC Report at p. 3

In pre-covid times (2019), the TTC operated 145.1 million km with its bus fleet. At a saving of about 1.38 kg CO2/km, this translates to 200,000 tones of CO2, a somewhat lower figure than the TTC claims.

As Toronto launches into a new electric era, the TTC needs to clean up its statistics and calculations so that those trumpeting our efforts use the correct data.

Environmentalists, transit boosters, city planners, anyone who is touting electrification should be careful to cite correct figures for the expected benefit of eBuses.

I have no problem with “going green” and welcome the shift to electric vehicles. That said, it is important that the benefits be stated accurately and clearly so that “green” is not oversold. Toronto’s transit history is littered with hucksters.