Not only do these Airlines take into count ground delays for the aircraft b also take into factor passenger safety getting in and out of the airport. If the roadways are gridlock Ed yhen have many passengers are going the make their scheduled flights? I have been I Seattle during a snowfall and I-5 was literally a parking lot with abandoned vehicles left in travel lanes. Having grown up in Alaska I was able to navigate the roads just fine however even in Anchorage after the first snowfall just have many wrecks/stranded motorists do you see? Many! So safety is a priority to reputable companies or so I hope...