Either:-
a) Liaise via phone with TOC control rooms, National Rail's info controllers (the website folk) and light rail companies to compile pieces of text to be sent direct to all BBC local radio stations, a considerable number of commercial stations, BBCi, ITV Local, Teletext, Transport Direct and an assortment of other media organisations.
b) Same as above but for individual flight and ferry alterations at 32 UK airports and approx 15 ferry operators respectively. We also do buses if there's something big going on, such as the recent closure of central Woking which brought traffic to a standstill for quite some time after the discovery of a suspicous item.
All done by two people on a national scale - one person covering each of the above - at an office in London (or after 5pm weekends just yours truly doing it all single handedly

).
If you're ever in a position to get London Today news broadcasts during GMTV then tune in to see our ITV bulletins (there's a few on YouTube if you do a search for 'Trafficlink' or 'Annoyed Presenter')