YOU SAID:
The cat is riding down mainstreet
INTO JAPANESE
猫はメインストリートを下って乗っています
BACK INTO ENGLISH
The cat rides down the main street.
INTO JAPANESE
猫はメインストリートを下ります。
BACK INTO ENGLISH
The cat is down the main street.
INTO JAPANESE
猫はメインストリートを下っています。
BACK INTO ENGLISH
The cat is down the main street.
That didn't even make that much sense in English.