Instead of high-speed rail, why not develop airplanes that are more environmentally friendly?

Along with world peace and the elimination of poverty and disease?

There are so many problems with aircraft in a densely populated area that their primary benefit is over longer distances or to less populated ones.  Airports alone are not environmentally friendly in a big city.

If I told you how much passenger jets have changed over the past 30 years to make them lighter and more fuel-efficient  (things like replacing steel with plastic and eliminating those pesky redundancies that protect against system failures) you'd probably never fly commercial again...

High speed rail is a joke and a boondoggle.

Despite my warnings, the voters here in CA approved it about a decade ago, and tens of billions later, less than 65 miles of track have been laid, from nowhere to nowhere.

Not only that, this bullet train that was supposed to go from LA to SF was completely unneeded as each metro area is served by 3 airports that can do the trip quicker than a bullet train ever could.

Because there are a lot of advantage to high-speed rail over planes. They're cheaper to run, they can transport more people and goods, planes get empty or full, but trains you can add or remove cars, and trains aren't as susceptible to bad weather. They can also stop in more places en route, as a train stopping at a town is quick, and a plane has to land and take off.

While they're at it, maybe they should be working on transporters to beam people around the planet.

Airplanes will never even come close to the fuel efficiency of trains. 

Trains can make multiple stops much more efficiently than airplanes.

I, as well as many others, think train travel is much more comfortable and pleasant the commercial air travel.

Electric powered planes are being developed.  High speed rail is a better option though for intermediate distance travel.  I have used them in other countries.   The terminals are in the heart of the city, you don't need to arrive hours ahead of time to board, and delays and cancellations are much rarer.

simple answer really..it takes more energy to fly because of gravity....meaning it needs more fuel/energy per/km..and vastly increasing air traffic, as well as the former, would also mean higher chance of air accidents, and unlike most road accidents, air accidents are fatal

an additional point and one that i would argue is the whole basis of the argument to increase air traffic, is the relative speeds, however over shorter distance this difference  in reality isn't as significant, because aircraft take time to  be allowed to land and have much higher time to prepare for departures  (pre flight check list), that the time difference for a given journey, does not compensate for the difference in needed energy, the other points have been correctly made my @Scott.B

So you see in reality, it's a no brainer

Because I wanna go fast on land. 

Let's make wings for them and people can flap them to make it fly!!!