Answer: Designated bike lanes have reduced traffic-related accidents by 43 percent in other cities.
Step-by-step explanation:
From the information given in the question, the city planner believes that the bike lanes will help drivers and cyclists avoid accidents, and also make the downtown area more attractive to bike commuters.
Based on the above, the fact that best supports the city planner’s opinion is that designated bike lanes have reduced traffic-related accidents by 43 percent in other cities.