Laws requiring the use of headlights during daylight hours can prevent automobile collisions. However, since daylight visibility is worse in countries farther from the equator, any such laws would obviously be more effective in preventing collisions in those countries. In fact, the only countries that actually have such laws are farther from the equator than is the continental United States.

请问有没有人知道黄色部分这句话的意思和语法结构，该句来自11th-Review 44, OG的解释是：The only countries having these laws are those located farther from the equator than is the continental U.S,谢谢。

我能读懂句子的意思，但是想不通这个比较句的是如何省略的。这个比较句的省略中，is的作用是什么呢？还有only的意思？能不能请教把than后面的句子全部恢复。实在抱歉，我是新手。