找出下列句子的一处 语法错误：

　　When smart traffic lights are set up and traffic management softwares are installed, the number of green lights on each street has been optimized to avoid traffic congestion as well as to allow ambulances to reach incidents without any delay.

　　♜ 适用考题：

　　The most important problem affecting our society today will be solved in our lifetime. (2012.10.27)