Getting rid of cars as much as possible in congested areas is the best way. Promoting very good public transportation and prioritizing people walking and riding bicycles.
If they optimize the flow of cars in a little time there will be more people using cars in those areas and no operations researcher can solve that bigger traffic jam. People, like any biological entity, adapt to the environment.
buses, trucks, emergency vehicles, bicycles on the roads, taxis, people going places too out of the way for public transportation to service and whatever other uses of the roads that aren't immediately obvious would all still benefit from this.
smoother traffic flow and reduced time on the roads would also reduce accidents, which would require fewer vehicles be manufactured, which is a nontrivial environmental impact in and of itself. oh and fewer humans would die in horrific accidents.
If they optimize the flow of cars in a little time there will be more people using cars in those areas and no operations researcher can solve that bigger traffic jam. People, like any biological entity, adapt to the environment.