If you make it easier and quicker to drive, more people drive. If it is not so easy to drive, fewer people will drive or they will drive less. The net result of reducing lanes is less traffic, not gridlock.
Over the past 20 years, the French city of Paris has been gradually and progressively reducing the priority placed on automobile movement and increasing the space given to walking, cycling and transit.
Source: Remove it and They Will Disappear – Raise the Hammer