**一倍**

**Tuttle's Learners**
>fold, time

>这个学校的学生人数比我们学校多一倍。(=这个学校的学生人数是我们学校的两倍。) 

>Zhège xuéxiào de xuésheng rénshù bǐ wǒmen xuéxiào duō yí bèi. (= Zhège xuéxiào de xuésheng rénshù shì wǒmen xuéxiào de liǎng bèi.)
The student number of this school is twice as big as that of our school. (—> The student population of this school is twice of ours.)

多一倍 is translated, first in Chinese as 两倍 so it's easy to see how confusing this phrasing is! But....

**两倍**

**Oxford**
>② [indicating difference in quantity]

>这一带水稻产量比小麦高两倍 

>The output of rice is three times that of wheat in this area

两倍 has become **three times** here(!).

**but**(!) - still from *Oxford*:

>你的工资相当于我的两倍。 

>Your salary is twice that of mine.

Basically you've really got to look at the context to figure out the meaning!

Your sentence above 
`开车最少比骑自行车快一倍。` the 快 here has the same effect as 多 so it's really saying it's "one time as fast" which is really "twice as fast"...

Hope that makes sense