Throughout the London region, construction crews are burrowing tunnels, laying track and beginning to build new stations as part of the largest addition to the city's public transportation system since World War II.

But even before the crews arrived, investors were making big bets on how the new system, named Crossrail, will change the game board of one of the biggest real-estate markets in the world. Speculators have been bidding up values of properties near the new stations on the route.