YOU SAID:

i ran into my best friend while driving over a mountain

INTO JAPANESE

私は山の上を走行中に親友に出くわした

BACK INTO ENGLISH

I ran into my best friend while driving up the mountain

INTO JAPANESE

山道を走行中に親友と偶然出会った。

BACK INTO ENGLISH

I ran into my best friend while driving on the mountain road.

INTO JAPANESE

私は山道を走行中に親友と偶然出会った。

BACK INTO ENGLISH

I ran into my best friend while driving on the mountain road.