大陸 たいりく横断 おうだん鉄道 てつどうだったら
tairikuōdantetsudōdattara

Noun
Da Copula

The "-tara" conditional form ("if/when…") of 大陸横断鉄道

1. If it were the transcontinental railroad; If the transcontinental railroad existed

Tara Conditional