Note that the measurements are often cited per passenger. Part of the spat between Boeing and Airbus over their next gen ~150 seat passenger planes (737max & A320neo)[1] is over how many passengers are used in the calculations (maximize for your own plane, minimize for the other guy). To get an idea of how the argument goes see this article starting in the "war of words" section which gives a good idea of all the factors making up the cost of flying: http://www.aspireaviation.com/2012/07/20/boeing-737-max-ups-...
The efficiency improvements come from all over the place including dealing with wing tips (fences, winglets, "sharklets"), weight reductions (lighter materials, redesigned components) and engines (weight, gearboxes, compression ratios).
The plane manufacturers and engine manufacturers are constantly doing tweaks to give improvements, usually managing around 1% per year. Search for "performance improvement package" to see numerous press releases and articles.
In the future there are blended wing bodies and open rotor engines that have another leap in efficiency.
[1] The tradeoffs are very similar to what we see in the IT industry. For example the 737 is lighter and sits lower to the ground. That means it can't use larger diameter more efficient engines. And makes it more efficient for shorter routes due to less weight, but the heavier higher A320 can then be more efficient over longer routes. Every change made involves retooling and recertification so it isn't a simple decision to just do everything possible. And newer better planes effect the residual values of older planes which makes lessors potentially less likely to buy your newer planes due to economic uncertainty. There was a lot of debate and speculation about re-engining the existing models, re-winging too, fuselage material changes etc.
The efficiency improvements come from all over the place including dealing with wing tips (fences, winglets, "sharklets"), weight reductions (lighter materials, redesigned components) and engines (weight, gearboxes, compression ratios).
The plane manufacturers and engine manufacturers are constantly doing tweaks to give improvements, usually managing around 1% per year. Search for "performance improvement package" to see numerous press releases and articles.
In the future there are blended wing bodies and open rotor engines that have another leap in efficiency.
[1] The tradeoffs are very similar to what we see in the IT industry. For example the 737 is lighter and sits lower to the ground. That means it can't use larger diameter more efficient engines. And makes it more efficient for shorter routes due to less weight, but the heavier higher A320 can then be more efficient over longer routes. Every change made involves retooling and recertification so it isn't a simple decision to just do everything possible. And newer better planes effect the residual values of older planes which makes lessors potentially less likely to buy your newer planes due to economic uncertainty. There was a lot of debate and speculation about re-engining the existing models, re-winging too, fuselage material changes etc.