Whenever I need to go to the bank, the parking lot is always full, but when I don't have any errands to run, there're always lots of parking spots available.
この場合、次のような言い方ができますよ。
ーWhenever I need to go to the bank, the parking lot is always full, but when I don't have any errands to run, there're always lots of parking spots available.
「銀行に行かないといけない時はいつも駐車場は満車なのに、用事がないときはいつも空いている」
to have errands to run で「用事がある」
ご参考まで!
The parking lot is open only when I don't need to go there.
The parking lot is open only when I don't need to go there.
「用事がないときに限って駐車場は空いている」
parking lot は「駐車場」という意味です。
例文:
The bank parking lot is always full when I have business, but it's open only when I don't need it.
「銀行に用がある時はいつも満車なのに、用事がないときに限って駐車場は空いています。」
お役に立てれば嬉しいです。