GMAT Critical Reasoning (CR) | Re: The heavy traffic in Masana is a growing drain on the city's economy

Hi daagh,
I am not satisfied with the explanations above for taking C to be better than A.
If A needs an assumption that Most of vehicles from these 20% outside vehicles will take alternate road because of the new rule.
So does C, C needs assumption that what worked in other city will work in the Manasa.
Sir, Can you please throw some light in this question.
Thank you.

The heavy traffic in Masana is a growing drain on the city's economy - the clogging of the streets of the central business district