On 23/10/2012 16:58, Arfa Daily wrote:
On last week's episode of Eddie Stobart Trucks and Trailers, they showed
driver Mark working with a new illegal-length trailer that they have
been given special dispensation to trial on UK roads, by the DoT. They
said that it was called an "Eco-trailer" because being some 2 metres
longer than a 'standard' trailer, it would be able to carry nine more
cages of Tesco goods, which would mean less lorries on the road leading
to a fuel and pollution saving.

Fair enough, I thought. But later whilst giving it a bit more
consideration, I started to think about the 'not getting owt for nowt'
principle, and started to doubt whether there really is any 'free lunch'
to be had here. If the 'standard' trailer is about 13 m long, then this
one at 2 m longer represents about an extra sixth of a truck. So for
every six of these new trailers, you'd save one standard tractor unit
and trailer. But then, you've got to take into account that the extra 2
m of trailer is going to weigh quite a bit, as is the extra axle and
tyres that it had, and the extra equipment to make the rear axles
steerable so that it can get round roundabouts, and manoeuvre in tight
yards. On top of that, there will be the additional frictional drag from
the extra axle, plus the weight of the nine extra cages, and the goods
in them. Hauling those additional weights and losses, is going to take
more engine power, and will thus use more fuel. So how much fuel usage
advantage would really be gained from these extra long trailers ? Any ?
Rather less than was implied ? And as for reducing pollution, I know
that diesels aren't the cleanest of engines, but as far as I am aware,
they produce little or no carbon dioxide, which is the one that the
green mist brigade are terrified of, and only small amounts of carbon
monoxide, so is this just another case of adding the word "Eco" to the
front of some existing item, to justify getting what might be a
contentious change to that item, accepted ? Or am I just being cynical
in thinking that if Stobarts got the approval to roll this out across
their fleet of curtain-siders, they would save the wages of one sixth of
their drivers ... ?

At speed the main loss for a lorry will be air resistance. An extra bit
on the trailer won't add much to that. So yes, it'll use more fuel than
the shorter one, but not that much more, and if used wisely it'll use
less per unit delivered.

CO2 production by a diesel engine is pretty much directly proportional
to the amount of fuel used, and the main combustion products are CO2 +
water - not "little or no carbon dioxide" at all. CO2 isn't about
cleanliness of burning, it's just what gets produced when you burn a
carbon-based fuel with adequate oxygen.