Freight Factor: Payload-specific Fuel Efficiency
Traveling one-up in a semi-static sea of cars all headed to or from work in peak-hour traffic is practically a metaphor for envirogeddon. Not only is it the antithesis of enjoyable driving, it’s a profligate waste of energy. Some in the community are quick to point an accusatory finger at motorists, but the real blame in Australia rests with state governments, which have steadfastly, over decades, allowed public-transit infrastructure to grind practically to a halt. In the absence of a viable mass-transit system, there’s … driving. And everyone does it. With the end of oil at least foreseeable, and in the face of rampant global demand, something really should be done.
Odds-on (unless you endured more than the odd propeller-headed university physics course) you’ve never looked at fuel consumption quite like we’re about to now.
A great truth about fuel efficiency and consumption is frequently swept under the rug, conveniently, because you probably don’t think of yourself as ‘payload’. Statistically, nobody calculates their car’s payload-specific fuel efficiency. Doing so gets depressing in a big hurry anyway. People consider absolutes instead – like this: Cars drink about 11 litres per 100km whereas articulated trucks gulp about 55 litres per 100km. Therefore cars are five times more fuel efficient than trucks, right?
Let’s say you and your briefcase trot off to work; total mass 100kg. You get into the average Australian passenger car, which according to the Australian Bureau of Statistics (Survey of Motor Vehicle Use 2006) consumes 11.3 litres per 100km.
It seems pretty low – unremarkable, even – until you look at it like this: You’re the payload. And you’re a very small proportion of the all-up mass (probably about one-fifteenth). That means fourteen-fifteenths of the fuel you tip down the filler neck moves the metal – only one-fifteenth moves you.
If it takes 11.3 litres to move 100kg of you a distance of 100km, the ‘cost’ in fuel to move one tonne of people just like you is 113 litres per 100km. This is very inefficient.
If you think of 11.3 litres per 100km as the car’s absolute fuel consumption, calculating the payload-specific figure (113 litres per 100km per tonne) allows you to compare the relative efficiencies of all different kinds of transport. It normalizes all the results for payload carried – allowing apples-for-apples analyses. And the result is enough to make your head spin.
Here’s how the heavyweights really stack up:
Payload: 100kg (you)
Average fuel consumption: 11.3 litres/100km (source: Ausstats)
Payload-specific fuel consumption: 113 litres/100km/tonne
Conclusion: Oh dear…
LIGHT COMMERCIAL VEHICLE
Average Payload: 460kg (source: Ausstats)
Average fuel consumption: 13.0 litres/100km (source: Ausstats)
Payload-specific fuel consumption: 28.3 litres/100km/tonne
Conclusion: The ubiquitous tradie’s ute or van typically drinks 15 per cent more than the average car in absolute terms, but is exactly four times more efficient as a per-tonne payload conveyance than the average car.
Average Payload: 5624kg (source: Ausstats)
Average fuel consumption: 29.6 litres/100km (source: Ausstats)
Payload-specific fuel consumption: 5.26 litres/100km/tonne
Conclusion: With an average load of 5.6 tonnes aboard, the rigid truck shows just how efficient machines get when the payload is a serious proportion of all-up weight. Despite almost triple the thirst of an average passenger car – per kilometer – the rigid truck is 20 times more efficient at moving payload than a car with one passenger aboard.
Average Payload: 24,112kg (source: Ausstats)
Average fuel consumption: 55.6 litres/100km (source: Ausstats)
Payload-specific fuel consumption: 2.31 litres/100km/tonne
Conclusion: You might not enjoy dicing with semi-trailers and B-doubles in traffic (who does?) but it’s a good thing all that freight isn’t being transported in the boots of cars instead – unless you’d like the transport cost component built into the price of basically all consumer goods to jump … fifty-fold.
Estimated Average Payload: 2000kg (20 people and luggage)
Average fuel consumption: 26.8 litres/100km (source: Ausstats)
Payload-specific fuel consumption: 13.4 litres/100km/tonne
Conclusion: Thinking of picking the low-hanging fruit from the ‘fuel conservation’ tree? Catch the bus instead. Peak-hour traffic’s no fun in any case. A half-full bus is almost 10 times more efficient that you on your lonesome in your car.
Estimated Payload: 50,000kg (max. 568 people, source: Boeing)
Average fuel consumption: 1200 litres/100km (source: Boeing)
Payload-specific fuel consumption: 24 litres/100km/tonne
Conclusion: Okay – reality check – no, you can’t drive to Singapore, and, yes, the office is way too close to fly. A Boeing 747 drinks fuel faster than you can pour it from a jerry can: four litres per second, on average. That’s 12 litres for every kilometer, or a massive 150,000 litres in the course of a 10-hour flight. But it compares very favourably (at about four times better) to driving anywhere one-up. In fact, in the payload-specific fuel-efficiency stakes, flying at 30,000 feet is about the same as driving anywhere with four people aboard the average car – not to mention getting there eight times faster than the freeway limit.
CONTAINER SHIP EMMA MAERSK
Maximum Payload: 154,000,000kg (11,000 14-tonne shipping containers, source: Maersk)
Engine Output: 85,000kW
Payload-specific fuel consumption: better than 0.3 litres/100km/tonne
Conclusion: Irrelevant? Maybe – last time we looked it’s not a practical matter to sail the Emma Maersk to work with 1.54 million of your closest friends aboard. But it does demonstrate the logical extension of the concept. Just 300ml of hydrocarbons are required to push one tonne of payload a distance of 100km in the big Maersk container ship. In your average Aussie car, 113 litres – almost 400 times more – is required to do the same job. It’s the main reason why sea freight is dirt cheap.