U.S. Natural Gas Pipeline Network
http://www.eia.gov/pub/oil_gas/natural_gas/analysis_publications/ngpipeline/index.html
Not pipelines.
Market.
The US now produces more gas than it consumes. The ability to transport gas does not mean that you have a willing buyer.
If storage is full, and you have no buyer, then you flare or you shut in. The concern is that there will be no market for the volume of gas produced.