我觉得这里用either和each都可以,没什么区别,either side of the road 指“路两边中的任意一边”“路两侧中的任意一侧”,其实也就是指“路的两边或两侧”(=both sides of the road)或“路的每边或每侧”(=each side of the road)。比如下面两句摘自《韦氏高阶英语词典》的either词条:
Flowers bloomed on either side (=on both sides) of the walk.
Either (=Each) answer is correct. (=Both answers are correct.)