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