走 has both broad sense and narrow sense. so it is OK to ask 去图书馆怎么走？ when you ask this question while you are driving a car or riding a bike, people can know that you don't mean "walking" and it's pretty easy to emphasize the driving like: 怎么开车去图书馆？ 开车怎么去图书馆？ 图书馆开车怎么去？ 图书馆怎么开车去？ All of those are OK !!

怎么走 可以包括开车的情况，如果你开着车，然后问路人，你也可以直接问： 图书馆怎么走？ 你非要强调交通工具的话 ：怎么开（车）去图书馆？

tell you an universal way : 请问（= Please）+ 怎么（=how )+ V （eg 去/ 做/买...）+ N （ 地点/ 其他名词...）？ like: how to go the bus station ? → 请问怎么去公交站？ how to book for a ticket? → 请问怎么买票？

The first sentence, 图书馆在哪儿, focuses more on the location of the library. So, basically you'll receive descriptive replies such as the address of the library and the relative position, which are given by standing on the library's side to give the direction. However, the second sentence, 去图书馆怎么走, in contrast, is used for asking the direction based on your position at that time. Here, 走 is a metaphor to "reach/arrive or by walk". The answer to the last question is yes, you can substitute 走 with the approaches to get the destination by other vehicles such as 开车/搭公车/搭捷运/搭地铁/搭火车/骑机车. But, the grammar here might have to be slightly changed. Take your sentance for example, " 怎么开车到图书馆" make it sound more fluent in Chinese. Hope these are helpful for you. :)

When I hear 去图书馆怎么走？, I do try to find a walking way in my mind. But then I realize, I also ask people 去XX怎么走 when I was in my car. So 去图书馆怎么走 just mean how can I get to bibrary. It don't espically refer to By walking or by drive. By the way, we definitely won't say" 去图书馆怎么开车”。But I understand why you say this. 走 is a same verb as 开车, why not put it behind 图书馆?right? But we just don't speak like that. It sounds wierd. Are you interested in find a language partner? We can help each other on this.