The main problem with buses and the underground is their restricted opening hours and also the fact they don't go absolutely everywhere in the city.

restricted 是动词 restrict 的过去分词形式作形容词使用。restrict 由前缀 re-（表示"加强"）和词根 strict（严格的）组成，意思是"限制、约束"。restricted 在这里表示"受限制的、有限的"，指公交和地铁的运营时间不是全天候开放，而是有特定时间段的限制。