Trains are most useful for reaching areas of South London, more distant destinations such as Hampton Court Palace, or even further afield (to Windsor Castle, Oxford, Brighton, Cambridge or Bath). Services are run by independent private companies. You can use your Oyster Card on many of these routes with the correct zones.
Crossrail goes into service in 2019, a year or so behind schedule. The train, officially known as the Elizabeth Line, runs from Reading in Berkshire and Heathrow, through central London, and then branches south to Abbey Wood and east to Shenfield in Essex. Ten new stations have been specifically constructed for the endeavour, while 30 other stations have been integrated into the plan.