Selling Downtown LA's Empty Air

The sale of the empty space above buildings has been a device for historic preservation.  Instead of tearing them down, developers leave structures in place and build new ones equal in size to the original square footage, multiplied by a certain number of stories.  Now, the City of Los Angeles wants to sell the so-called "air rights" above the Convention Center, not to preserve it, but to increase urban density. What sounds like a joke is instead an opportunity to turn the empty space into high-rise residential development. That space converts to seven towers 73 stories high. That's the size of the US Bank Building and it's set to go on sale at $20 a square foot. Is the price right?  What about traffic congestion?  We ask an urban planner and the councilwoman who represents the area.