Learn Spanish (Latin America): Aquí se permiten los transbordos, lo que es útil. - Transfers are allowed here, which is useful.

In the reflexive passive (pasiva refleja), the thing receiving the action actually acts as the grammatical subject. Since los transbordos (the transfers) is plural, the verb must also be plural (permiten) to match it. Grammatically, it's as if you're saying "transfers allow themselves."

Can I just treat los transbordos as the object and say "se permite los transbordos"?

No, that's a common mistake! Because los transbordos is a noun (and not a person preceded by the personal "a"), it forces the sentence into the reflexive passive, meaning it becomes the subject and requires a plural verb. The always-singular impersonal "se" is only used when there is no grammatical subject (like aquí se come bien) or when the object is a specific person (like se busca a los ladrones).

Why do we need lo que here instead of just que for "which"?

When "which" refers back to an entire situation, clause, or abstract idea—rather than a specific noun—you must use a neuter pronoun like lo que or lo cual. Here, "which" refers to the whole preceding fact (that transfers are allowed), not to the transfers themselves. If you just used que, it would incorrectly refer only to los transbordos.

What kind of "transfers" does transbordos refer to?