Category Archives: Transport

Tracking performance of light vehicles

Here is a monitoring challenge: suppose you want to do a weekly check on the performance of a small fleet of hotel minibuses. Although you can record the mileage at the end of each week, you will have a lot of error in your fuel measurement because you’ll only know how much fuel was purchased but not when. How can you adjust for the inconsistent fuel tank level at the end of the week?

One method would be to use the trip computer display which will show the estimated remaining miles (see picture). The vehicle in question has a 45-litre tank: at its typical achieved average mpg, it has a range of 613 miles of which it has used 39%, so we can add 45 x 0.39 = 18 litres to our calculated fuel consumption. Note that we will need to deduct an equal amount from next week’s consumption, and this “carry forward” is likely to reduce the error in the adjustment.

This procedure also helps if drivers do not consistently fill to the top. To the extent that they underfill on the last occasion in the week, the shortfall will increase the adjustment volume to compensate. The adjustment can only ever be approximate, however, so it’s better if they consistently brim the tank.

The other advice I would give is to track not miles per gallon (or any similar performance ratio) but to plot a regression line of fuel versus distance. This will pick up, and detect changes in, idling behaviour.

Carbon emissions – a case of rubbish data and wrong assumptions

The UK Government provides tables for greenhouse gas emissions including generic figures for road vehicles. For example a rigid diesel goods vehicle of 7.5 to 17 tonnes has an indicative figure of 0.601 kg CO2e per km. You need to apply such generic figures with caution, though. I saw a report from a local council that used that particular number to back-calculate emissions from its refuse collection trucks. Leaving aside the fact that many of their vehicles are 26 tonners, they spend much of their time accelerating, braking to a halt, idling and running hydraulic accessories, with the result that one would expect them to do no better than about 4 mpg with emissions more like 1.8 kg CO2e per km, three times the council’s assumed value.

For the council in question that is not a trivial error. Even on their optimistic analysis domestic waste collection represents 33% of their total emissions. Properly calculated (ideally from actual fuel purchases) they will turn out to be more than all their other emissions taken together.

Further reading


For sustainability professionals to make a real practical difference to carbon emissions they need a broad appreciation of technical energy-saving opportunities. To help them understand the potential more clearly I run a one-day course called ‘Energy Efficiency A to Z‘. Details of this can be found at


Ultra-rapid charging

StoreDot and BP present world-first full charge of an electric vehicle in five minutes” runs the headline on this news item from BP which actually talks about an electric scooter. The Storedot website is a bit more gung-ho about their new battery technology, which they think would enable a 5-minute full recharge of an electric car with 300 mile range. Really?

Quick sense check: for a 300 mile range you’d be talking probably about a 100-kWh battery for which a 5-minute full recharge would demand 1.2 megawatts of charging capacity. That’s going to be some meaty charger. Moreover, even upping the charger voltage to 1,000 volts you’ll be drawing 1,200 amps, so I reckon the charger cables are going to need a pair of conductors of (say) 4 square centimetres cross section. And cars would need to be engineered with DC charging circuits to match …

I put these points to StoreDot and they pointed me to Chargepoint’s website which talks about “up to 500 kW” Express Plus charging using the CCS Type 2 connector, although as far as I know CCS2 goes nowhere near that rating and when those kinds of powers are achieved they are going to need thousand-volt water-cooled charging cables with thermal sensing on the plug because of the risk of overheated contacts.

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Back to the scooter that BP had seen recharged in 5 minutes. The  model in question has two 48V 31.9 Ah batteries (so about 3.1 kWh) which to recharge in 5 minutes would require a 37 kW charger – plausible in a non-domestic setting. I imagine the demonstration to BP involved removing the batteries to recharge them because obviously the scooter’s onboard electrics would not be designed to handle a charging current of 800 amps.

My colleague Daniel did some digging and unearthed this priceless video from StoreDot in 2014, purporting to show a smartphone being completely recharged in 30 seconds using battery technology that would be released in 2016 (I’m still waiting…). The sceptical comments are worth reading — especially the ones about fake phone screens, and indeed the ones about exploding phones — but you can’t help but notice in the video itself they are actually “charging” a huge battery glued to the back of the phone. So a big dose of scepticism is in order, I think, and if the link to the video no longer works you can guess why.

More credible is the news this April about battery developments using vanadium disulfide cathodes stabilised with a microscopic layer of titanium disulphide: this promises faster charging but they are careful not to say how much faster.