Learn Hardcore Korean: jigeum giri manhi makhyeoyo. - There is a lot of traffic right now.

지금 길이 많이 막혀요 presents new information neutrally: “The road is (indeed) very jammed now.”
지금 길은 많이 막혀요 contrasts or highlights the road as the topic (e.g., “As for the roads now, they’re very jammed,” maybe implying other things aren’t, or compared to another time/place).

Why is the passive verb 막히다 used instead of the active 막다?

In Korean, traffic/roads being jammed is expressed with the passive/intransitive verb 막히다 (“to be blocked, to get jammed”). Using 막다 (“to block [something]”) would require an explicit agent and doesn’t describe traffic conditions. So you say 길이 막혀요 “the road is jammed,” not “길을 막아요.”

What exactly does 많이 mean here? Could I use 너무 or 아주 instead?

많이 = “a lot/very much” (neutral intensifier for verbs/adjectives): 길이 많이 막혀요.
너무 = “too/so (much)” (often a stronger, more emotive complaint in speech): 길이 너무 막혀요 (“It’s way too jammed”).
아주 = “very/really” (a bit formal/literary; less common in everyday speech for this line): 길이 아주 막혀요.
Other colloquial intensifiers: 정말/진짜/엄청/되게 막혀요.

Is 막혀 있어요 or 막히고 있어요 more natural? What’s the difference from 막혀요?

막혀요 is the usual, all-purpose way to say “is jammed” right now.
막혀 있어요 emphasizes the resulting state: “is (sitting) in a jammed/blocked condition.”
막히고 있어요 means “is in the process of becoming jammed,” and is used only when you want to stress that the jam is forming right now. For traffic reports, 막혀요 (or 막혀 있어요) is normally preferred.

Can I move 지금 elsewhere in the sentence?

Yes. Common options:

지금 길이 많이 막혀요 (default, most natural)
길이 지금 많이 막혀요 (focuses “now” inside the clause)
지금은 길이 많이 막혀요 (contrasts now with other times) Placing 지금 at the very end (…막혀요, 지금) can occur in casual speech as an afterthought, but it’s less typical.

What politeness level is 막혀요, and how would I say it casually or more formally?

Polite informal (most common): 막혀요
Casual (friends, same age): 막혀
Formal polite (announcements/news): 막힙니다
Past forms follow the same style: 막혔어요 / 막혔어 / 막혔습니다.

Is it more natural to say 길이 막히다, 차가 막히다, or 교통이 막히다?

All are used:

길이 막히다 and 차가 막히다 are both very common in everyday speech.
교통이 막히다 is also correct, a bit more general/formal (“the traffic is jammed”).
Other natural phrases: 교통 체증이 심해요 (“traffic congestion is severe”), 정체예요 / 정체되고 있어요 (“there’s a standstill/congestion”).

How do I pronounce the words here?

지금 ≈ “ji-geum”
길이: the ㄹ links to the vowel and sounds like a light “r” → roughly “giri”
많이: spelled with ㅎ but pronounced without the h sound → “mani”
막혀요: the ㅎ causes aspiration; it sounds like “ma-kyeo-yo” (often heard close to “ma-kyeo-yo/ma-kyeo-yo”).
A simple romanization: jigeum giri mani makhyeoyo.

Can I drop the subject 길이?

Yes, if context makes it clear you’re talking about traffic.

지금 많이 막혀요 (“It’s really jammed right now.”)
Subject omission is very common in Korean when the topic is understood.

How do I say this in the past or future?

Past: 아까 길이 많이 막혔어요 (“The road was really jammed a little while ago.”)
Future: 오늘 저녁에 길이 많이 막힐 거예요 (“The road will be very jammed this evening.”)
You typically wouldn’t pair 지금 (“now”) with a past tense.

Do I need to make 길 plural (e.g., 길들) to mean “the roads”?

No. Korean often leaves number unstated. 길이 많이 막혀요 can mean “the road is jammed” or “the roads are jammed,” depending on context. Use plural 길들 only if you need to stress plurality, which is rare here.

Any common mistakes to avoid with this sentence?

Spelling: 많이 (not “많히”).
Verb choice: use 막히다 (not 막다) for traffic conditions.
Progressive: don’t overuse 막히고 있어요 unless you mean “it’s becoming jammed.”
Spacing: write each word separately → 지금 길이 많이 막혀요.
Particles: after a consonant, use 이 (→ 길이), not 가.

Is 막히다 a ㅎ-irregular verb?

No. 막히다 is not one of the ㅎ-irregular adjectives like 하얗다/파랗다. Its ㅎ is part of the stem 히, and it conjugates regularly: 막혀요, 막혔어요, 막힐 거예요, etc.

How else can I say “Traffic is heavy right now”?

지금 차가 너무 많아요.
지금 길이 복잡해요.
지금 교통 체증이 심해요.
지금 정체예요.
All sound natural, with slightly different registers/nuances.