I want to know what (is) the most (ordinary) (means ) of transportation.
或
I want to know what (is) the most (common) (means ) of transportation.
或
I want to know what (is) the most (common) (forms ) of transportation.
参考资料：
火车是一种安全的交通工具.
The train is a safe means of transportation.
最快的交通工具是飞机.
The quickest means of travel is by plane
离开机场的交通工具通常是什么?
What are some of the common means of transportation to leave the airport?
是啊,这是我最常用的交通工具.
Yes,this is the form of transportation I use most often.
Means of transport
牛津初阶英汉双解词典（第二版）-...
Space外层空间
Means of transport交通工具
Electronics电子设备 ... I want to know what (is) the most (ordinary) (means ) of transportation.
或
I want to know what (is) the most (common) (means ) of transportation.
或
I want to know what (is) the most (common) (forms ) of transportation.
参考资料：
火车是一种安全的交通工具.
The train is a safe means of transportation.
最快的交通工具是飞机.
The quickest means of travel is by plane
离开机场的交通工具通常是什么?
What are some of the common means of transportation to leave the airport?
是啊,这是我最常用的交通工具.
Yes,this is the form of transportation I use most often.
Means of transport
牛津初阶英汉双解词典（第二版）-...
Space外层空间
Means of transport交通工具
Electronics电子设备 ...