What's the most fuel-efficient lane on a highway? It's the middle. When you choose to drive in the middle lane of a three-lane highway, it gives you the flexibility to pass slower cars and allows faster cars to pass you or merge to exit the highway easily. The reason is simple: When you accelerate or decelerate less, you use less fuel and can maintain a steady speed that also includes fuel-efficient coasting. The more coasting and steady driving you can maintain, the better the gas savings in the long run.