How many runways do they use at once

They will only use runways heading into one general direction, eg. North. This is decided based on the wind direction. If I am correct, then Aircraft will generally takeoff and land into headwind if permittable.

Actually that's incorrect.

http://www.verorolfe.com/flying/chicagoops.htm
(all the way towards the end)

or

http://www.bigairport.com
(select pilot info I believe, then a runway config from the drop down list)

Those are some examples of multiple runway uses at Chicago. A place like LaGuardia (near me) will pretty much ALWAYS use both runways (at 90 degrees from eachother) unless the winds are heavy enough.

The reason for this is if you're a skilled ATC, timing the runway crossings with landing/departing planes isn't entirely to difficult, and it certainly cuts down on the enormous waits that programs like Ultimate Traffic will give you in conjunction with the default ATC's one runway (or two if there's a L & R) policy. Obviously, you will always prefer landing/departing into the wind, but when the winds are reasonably mild a crosswind landing or takeoff isn't that big of an issue.

Yes very true. Here at MKE we use 19R most of the time for takeoff's and then use basically anyother runway for landings.

Many large airports with parallel runways allow simultaneous approaches to both runways. Of course it will depend on the distance between the two runways. Only if the distance is great enough to do it safely will both runways be used at the same time.

In the case of airports with intersecting runways, ATC may clear an aircraft to "land and hold short" of the intersecting runway. It is the pilots decision-- if he thinks he can stop before he reaches the intersecting runway he can accept the clearance. Full responsibility for safety is on the pilot. 😎

Cheers guys thats been a great help! much apprichated. 🙂 happy flying

The folks stating airports use multiple runways at the same time are correct. Sometimes, a strong wind will dictate the use of a particular runway heading for landing and departure, however, if the airport has parallel runways, both will often be used. If the winds are lighter, it is very common at large and not-so-large airports for parallel runways to be used for arrivals and runways with entirely different headings to be used for departures.

One time at SFO, I was landing on RW28L. As I was on about a 3-miles final, a Boeing 747 took off in front of me on RW1R and just as I touched down, a DC-10 landed beside me on RW28R. That was sort of impressive from the left seat in my C-172.

Don are you an airline pilot?

No - I am not and have never been an airline pilot. I have a commercial license with multi-engine and instrument ratings and have been flying for over 33 years. For the past 15 years or so, I have been flying a Cessna 172. Prior to that, I flew a Cessna Turbo 210 both for myself and on contract to a large law enforcement agency.