Learn Spanish (Spain): Yo cojo la línea tres.

To keep the pronunciation consistent! In Spanish, the letter 'g' before 'e' or 'i' makes a soft, throaty sound (as in coger). But before 'a', 'o', or 'u', a 'g' makes a hard sound like in the English word 'go'. To keep that same soft sound for the 'I' form, the spelling changes to a 'j', creating cojo.

I've heard the verb coger is a bad word. Is it safe to use here?

Yes, it is perfectly safe and very common in Spain! In Spanish from Spain, coger is the standard, everyday verb for taking public transportation, grabbing something, or picking things up. However, in many Latin American countries, it has a vulgar meaning, so they use the verb tomar (to take) instead.

Why do we need the word la before línea? In English we just say 'line three'.

Spanish uses definite articles (el, la, los, las) much more often than English. When naming a specific thing like a bus route or a subway line, Spanish requires the article. Since línea ends in 'a', it is a feminine noun, so we use la.

Do I always have to say yo at the beginning of the sentence?

No, you can just say Cojo la línea tres. Because the verb form cojo already tells us the subject is 'I', the word yo isn't strictly necessary. Native speakers usually add yo for emphasis or contrast, like saying 'Well, I am taking line three (even if you are taking line four).'