No this isn’t a post on how to keep warm in winter 
Always hearing about a lorry fire on a road somewhere, and wondered what is the cause of these?
Do lorries have a design fault that lets them self combust?
Is it driver error i.e. cooking? 
Cars don’t seem to have this problem so why trucks?
If they go up when parked its usually electrical as the Stobbie saboteur found out.
I would suggest it is electrical, normally when a time served driver pretends he is a time served auto electrician.
Other reasons could be a failed injector pipe but that is probably rare because the smell and smoke is enough to warn you, and obviously binding brakes and hot tyres
Drivers plugging stuff into the power sockets, just because they are the same voltage doesn’t mean the socket can handle it.
A piece of advice/statement often seen on here - “If the fuse keeps blowing just put a bigger fuse in or use a bit of silver paper.”
If you get a trailer power lead that chafes through un-noticed and and starts arc-ing it can set the fifth wheel grease alight. Obviously the lead shouldn’t get thatbad and the grease shouldn’t be everywhere but it’s possible.
People putting hot ashes in the wheelie bins can help set a bin lorry off.
Or a grease gun falling across the battery terminals in the toolbox of a 360 excavator could cause the machine to catch fire. Probably 
I’ve noticed a lot more burn marks on the side of roads than I used to back in the 90’s. Twenty years ago I might see one every couple of months, now I seem to be noticing 2 or 3 a month. I assumed it’s because vehicles have more elastictrickery in them…
8wheels:
If you get a trailer power lead that chafes through un-noticed and and starts arc-ing it can set the fifth wheel grease alight. Obviously the lead shouldn’t get thatbad and the grease shouldn’t be everywhere but it’s possible.People putting hot ashes in the wheelie bins can help set a bin lorry off.
Or a grease gun falling across the battery terminals in the toolbox of a 360 excavator could cause the machine to catch fire. Probably
Blocked air filters,?
Had a problem with trailer brakes binding on the way to Reading years ago, did not realise they were binding slighty just thought it was the weight of the load, whilst on motorway heat was obviously being dispersed by airflow at 56 mph, when i got caught up in slow moving traffic on way through Reading town centre the heat travelled upwards through the trailer floor, had a full load of charcoal on board, the fire was intense to say the least, dropped trailer in road and saved unit 
inner tyres on twin axles being flat , crap maintenance, i.e. brakes , wheel bearing adj. , esp. when trailer is over max. weight, and (i know we should n"t) there is a fair way 2 go ,i.e. motorway.
Discarded cigarette and a trailer full of dry hay, makes for a warming fire! Boy does that burn…
Got held up a few years ago due to a car transporter packed with new BMWs that was well ablaze, everything was burning, very expensive. No idea what caused the whole lot to go up like it did.