Well, to throw the switch that deflects that train (a massive traffic surge) into your switchyard (your website).
So, if we extend the metaphor - how do we know a train is coming?
You listen to the telegraph.
And since that feature isn't on anyone's iPhone - what we're really talking about here is listening acutely to the media.
Television, radio, web news outlets - these are all conduits for massive amounts of public (or business) attention.
Attention means traffic.
There is an opportunity to bend public attention to your benefit - but it requires nimbleness - a good reaction time.
For example; a financial planning client is offering a service related to investments.
Careful monitoring of the news reveals topics that are not quite on the public 'radar' (a new program proposed in a government budget, for instance). However, if you were to put out some feelers (perhaps a very low-bid paid search campaign) - you would be monitoring in near-real-time what search traffic is searching for.
When search heats up on any of these terms you have staked out - you can then respond by creating a more robust response by beefing up content on the site, having a specific landing page with relevant actions.
These strategies are persuasive arguments for;
1) employing a long-tail approach to keywords in your paid search efforts
2) quick turnaround on producing content, and
3) frequently reviewing website analytics
So next time that train is a-comin', you get some heads up - and are even awake at that switch.