What are the latest ways to reduce the weight of aircraft, cars and ships? Are we talking new metal alloys or engineering practice?

Composite materials and highly optimized designs (use FEA to remove all unnecessary structural weight).

(1) Use carbon composites where you had not dared it before. Pray that the crash investigators find an other culprit.

(2) Compute the loads with a CAD, reduce all margins, check that judges haven't condemned someone for this before.

(3) Use better alloys or assembling techniques. Check that their weaknesses aren't known at the time you use them, so you wont' be hold for responsible.

 

Well, it's a simultaneous effort at materials, design, and everywhere. For instance, if you find a welding method (stir welding) that works for Al-Cu or Al-Zn alloys, you get both the better material strength and the better assembling technique.