The correct answer is: Only assumption I is implicit.
The statement says that the Municipal Corporation has decided to ban the entry of vehicles from sub-urban areas to the main city through main routes during peak hours to avoid traffic congestion. This means that the Municipal Corporation believes that the vehicles from sub-urban areas are causing traffic congestion during peak hours. Therefore, assumption I is implicit.
Assumption II is not implicit. The statement does not say anything about the traffic congestion caused by the vehicles of people residing in the main city. Therefore, it is possible that the traffic congestion is caused by both the vehicles from sub-urban areas and the vehicles of people residing in the main city.