Final answer:
Congestion Pricing is the most effective policy to reduce traffic congestion in a large metropolitan area by charging drivers during peak times, thus incentivizing alternative commuting methods.
Step-by-step explanation:
The policy most likely to reduce traffic congestion in a large metropolitan area, considering that people usually exploit opportunities to make themselves better off, is a) Congestion Pricing. This approach uses economic incentives to reduce rush-hour traffic by charging drivers a fee to enter congested areas during peak times. This provides a direct disincentive for driving during the busiest times, encouraging people to change their travel time, mode, or route. In contrast, while Road Expansion might seem like a good solution, it can lead to induced demand, which ultimately worsens congestion. Public Transportation Subsidies and Carpooling Initiatives are beneficial and promote shared transportation modes, but they don't directly charge individual car users for contributing to traffic congestion and might not be as immediately effective in changing driver behavior as Congestion Pricing.