By Fester:
My wife and I made a cannon-ball run to northern New Jersey to watch my mother in law graduate with her master's degree yesterday, so we spent way too much time on the Turnpike. And this is an observation that may be born of fatigue, but I spent a good 100 miles wondering why we did not see any overnight truck peletons in operation as a response to higher diesel prices.
If we assume constant speeds on a level surface (yeah, I know it is the PA Turnpike on the mountain route) an engine has to create enough force to counteract the work of two elements. The first is rolling friction which is a function of weight and the coefficient of friction between the road and the tires. The second is air resistance which is a function of frontal surface area, shape and speed. A more fuel efficient car of a given weight does something to minimize one or both sources of friction (as well as mechanical friction and heat production).
A peleton in bicycle racing is a highly organized cooperative structure of competing riders. Each rider in a pack takes a short turn leading the pack while everyone else tucks in tight behind each other. This formation allows the followers to 'free' ride against 30% to 40% less air resistance as the lead rider breaks the wall of air and creates a slip-stream where the resistance is far less. After a short period of time, the current leader then breaks formation and heads to the rear to recover and benefit from the next person breaking the wind. This formation at the Tour de France can go on for 100 miles as everyone conserves net energy compared to riding alone. The same concept is used in NASCAR and Indy racing to conserve fuel.
When we were driving on Monday night, it was common to see small convoys of two or three trucks traveling at intervals of 80 to 100 feet where there was some slipstreaming and drafting occurring. However there were no instances of turn sharing nor any very large formations. I find this odd.
Truckers' incomes are highly sensitive to fuel prices, and if a trucker can find a way to be 5% more efficient on a 1,500 mile run, that is a significant cost savings when diesel is at $4.50/gallon. It would be logical for cooperative efforts of non-co-workers to occur on the highway as it is a positive sum game. Cooperation allows all involved players to save on fuel costs. I wonder why this is not happening especially as there are large coordination and information sharing systems available to truckers including the ubiquitous CB radio, so setting up a small peleton of half a dozen trucks for the Pittsburgh to Philly run should not be difficult even if it improvised on the Turnpike itself? What is the blocking factor here?
This is mostly a guess, but I'm wondering how close behind you'd have to be tailgating for the drafting effect to be effective? Tractor-trailers don't exactly stop or even slow down on a dime, and so likely need more distance between each other for safety reasons. Race car drivers and bike racers and the like take the risk of being too close to avoid an accident because of the potential awards. Truck drivers don't really have that option.
ReplyDeleteBJ --- from what I have read, noticeable benefits start to accrue at 100 feet of distance --- more benefits as you get closer of course.
ReplyDeleteThe other term for that is drafting and, with trucks of widely varying shapes, sizes, weights, engine types and gear ratios, it is extremely difficult to do. A truck driver is shifting gears every few minutes on anything other than a dead level road and if they are travelling close enough to get a significant economy they will be too close to prevent a non-simultaneous shift from presenting a seriously dangerous situation. Travelling at close intervals also increases driver tension and fatigue. Finally, due to differing gear ratios, not all rigs have the same best economic speed.
ReplyDeleteOne thing to remember, they don't have to take turns in the lead to get the benefits. A lot (most? my knowledge is out of date) of the resistance from a truck is the void behind it. Nature abhors a vacuum, and the sudden absence of truck in the space behind it leaves a void that has to be filled in. Part of what fills it in is resistance to the trailer leaving. This is why most modern cars have rounded trunks and rear quarter panels: it helps to avoid the resistance by making it easier for air to fill the void. You'll note that most trucks have LARGE, flat, square tails.
ReplyDeleteWhat would it cost a trucking company to invent 'bubble' tail attached to the rear doors to reduce this drag?
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