Driving back and forth from the Upper East Side to the Upper West Side may soon be getting more difficult.The city said Tuesday that it is considering banning all cars from entering Central Park during the summer months.Mayor Michael Bloomberg says he has not talked to the transportation commissioner about the ban and had not yet decided if it would be a good idea.A poll by Transportation Alternatives found that among respondents one in ten visitors to the park were injured by a vehicle, and 64 percent would use the park more if vehicles were banned.