JJ.
In the very early days of the B707 operations, they towed the aircraft out to the runway threshold before take-off because they feared the jet engines would hurl molten bitumen across the tarmac. With experience, those fears faded, just as they will with the A380. The runways in LA are already big enough. It's just that they are narrow spaced paralell runways. Everything in LA is tight. Building another runway, if it is possible, which I doubt, would just make it tighter.