 This allows underpowered vehicles to remain in the existing "slow" lane without having to purposely pull left into the "slow" lane which drivers may not want to do because they then have to try to merge back into faster traffic (possibly still at low speed) when it ends.Instead, the more normal requirement to purposely pull out to pass slower vehicles, and back in after doing so or when the lane ends, generally with a smaller speed differential (as they will be rejoining what is already a passing lane), is placed on faster drivers.On normally 2-lane roads without a divider, the climbing lane effectively creates a bi-directional central passing lane of the original uphill running lane.