W tym przedziale jest cicho, bo większość pasażerów śpi albo czyta.

Because w here means in, so it requires the locative case.

• ten przedział = this compartment in the basic dictionary form
• w tym przedziale = in this compartment

Both words change:

• ten → tym
• przedział → przedziale

If w meant motion into something, then you could get the accusative in some contexts, but here the sentence describes location, so the locative is needed.

Here przedział means a train compartment or carriage compartment.

This word can have other meanings in other contexts, such as:

• an interval
• a range
• a section

But in a sentence about passengers sleeping and reading, the natural meaning is a compartment on a train.

Because cicho is an adverb, and in Polish adverbs are often used with jest to describe the general atmosphere or condition of a place.

So:

• jest cicho = it is quiet
• jest głośno = it is loud
• jest zimno = it is cold

By contrast:

• cichy / cicha / ciche are adjectives
• they describe a noun, for example cichy pasażer = a quiet passenger

So in this sentence, the meaning is not the compartment is a quiet object, but rather it is quiet in the compartment.

Bo means because and is very common in everyday Polish.

• bo = normal, spoken, natural
• ponieważ = more formal, more written, a bit more explicit

So this sentence sounds very natural with bo:

• ...jest cicho, bo większość pasażerów śpi...

You could also say ponieważ większość pasażerów śpi, but it would sound more formal.

Because większość means the majority of, and after it Polish normally uses the genitive plural.

So:

• pasażerowie = passengers
• większość pasażerów = the majority of passengers

This is very common in Polish:

• większość ludzi = the majority of people
• większość studentów = the majority of students
• większość książek = the majority of books

So pasażerów is not random: it is the expected form after większość.

Because the grammatical head of the subject is większość, and większość is singular.

So Polish treats it like:

• the majority ... sleeps / reads

That is why you get singular verb forms:

• większość pasażerów śpi
• większość pasażerów czyta

In the present tense, the singular form is:

• śpi = he/she/it sleeps
• czyta = he/she/it reads

Here they mean the majority sleeps / reads.

In other words, Polish grammar is following większość, not pasażerów.

Because Polish does not have a separate continuous tense like English is sleeping or are reading.

The regular present tense covers both ideas:

• śpi can mean sleeps or is sleeping
• czyta can mean reads or is reading

The exact meaning depends on context. In this sentence, the context clearly shows an action happening now, so English naturally uses are sleeping and are reading, but Polish just uses the normal present tense.

Both can mean or.

In this sentence, albo is a very natural everyday choice:

• śpi albo czyta = is sleeping or reading

A useful rough guide is:

• albo = common in speech, everyday
• lub = a bit more formal, often seen in writing or instructions

In many real sentences they overlap a lot. For a learner, the safest idea is that both can mean or, but albo often sounds more conversational.

Because Polish has no articles.

English says things like:

• the compartment
• the passengers
• a passenger

Polish simply does not use separate words for the or a. The meaning is understood from context.

So:

• w tym przedziale already means in this compartment
• większość pasażerów means the majority of the passengers or of passengers, depending on context

This is normal in Polish and one of the big differences from English.

Yes, Polish word order is more flexible than English, although the original version is the most neutral and natural.

The given sentence:

• W tym przedziale jest cicho, bo większość pasażerów śpi albo czyta.

is a standard way to say it.

You might also hear variations for emphasis, for example:

• Jest cicho w tym przedziale...
• Bo większość pasażerów śpi albo czyta, w tym przedziale jest cicho.

These are possible, but they change the emphasis or sound less neutral. For a learner, the original order is the best one to copy.