Learn Spanish (Spain): Hoy va a haber varias demoras. - Today there are going to be several delays.

This is the core rule of impersonal haber. Just like you say hay varias demoras (there are several delays) using the singular form hay, the same rule applies to verb phrases like ir a + infinitive. The verb takes the third-person singular form (va) because impersonal haber has no subject to agree with. Saying van a haber is a common mistake among native speakers, but it is grammatically incorrect.

Is varias demoras the subject of the sentence, and is that why people get confused?

No, in Spanish, impersonal haber doesn't have a subject. The phrase varias demoras is actually the direct object of the verb. Because English uses "there are" followed by a subject ("several delays"), English speakers naturally want to make the Spanish verb plural to match it. Remembering that demoras is the object, not the subject, helps explain why the main verb stays strictly singular (va).

What is the difference between demoras and retrasos?

They are mostly synonymous and can both translate to "delays". However, retraso is more common in everyday spoken Spanish for things running late, like trains, flights, or people. Demora sounds slightly more formal, and is often used in official announcements, business, or customer service contexts.

Could I move hoy to the end and say va a haber varias demoras hoy?