Here are the completed sentences:

6. We agree with the **ban** on the use of mobile phones while driving on the streets. (BAN)
7. There was a sudden traffic jam because of a(n) **accident** car breakdown. (ACCIDENT)
8. The city received a lot of **encouragement** for improving the roads and traffic signs. (ENCOURAGE)
9. To make the project successful, it needs the **involvement** of businesses and residents. (INVOLVE)
10. To reduce pollution, the city council needs to **encourage** the use of cars for short-distance commuting. (ENCOURAGE)