求问OG紫, 44题的一个解释

Laws requiring the use of headlights during daylight hours can prevent automobile collision. however, since daylight visibiliy is worse in countries farther from the equator, any such laws would obviously be more effective in preventing collisions in those counties.

 in fact, the only countries that actually have such laws are farther from the equator than is the continental United States.

这句话怎么也看不懂, 为什么这个than没有比较, 这句话如何解释成"美国大陆是唯一比那些的离开赤道远的国家对此法律更有效果的?  "