答案：A

考查同位语从句和固定搭配。involved in the popularity of private cars是problem的后置定语，__________ road conditions require __________是problem的同位语从句，讲的是problem的具体内容，且同位语从句意完整，用that引导；某事需要被做，可以用require to do或require to be done 结构。所以选A。