would have preferred 的理解

夸克语法大全 第四章 4.64 Mood markers: would and should

这一章的Note[a]最后一个例句是：

The journey was a disappointment to those who would have preferred to travel by road.

我一个人对这句话的理解是：这次旅程对于那些偏好公路来旅游的人来讲是一件让人失望的事情。

但其中的would have preferred这个动词结构改怎么样理解呢？

主句陈述的是过去的事实：这次旅游令部分人感到失望，而且这次旅游是乘飞机或船。这部分人those后接定语从句，从句谓语为传统语法的虚拟语气形式would have done，隐含了if they had had a choice这个与过去事实相反的虚拟条件。即假如这部分人当初可以选择的话，他们本来是想要乘车旅游的（事实是他们没选择，只能乘飞机或船）。所以定语从句用了虚拟语气形式would have preferred...。