asa nebousuru to, densya ni noriokuremasu.

朝 often works as a time expression, and many common time words in Japanese can be used without a particle.

So:

• 朝 寝坊すると… = If I oversleep in the morning...
• 朝に is usually unnatural here.

This is similar to other time words such as:

• 今日 行きます = I’m going today
• 明日 会います = I’ll meet [someone] tomorrow

A particle like に is often omitted with everyday time expressions.

Here, と is a conditional marker meaning something like:

• when
• if
• whenever

So 寝坊すると means:

• if [someone] oversleeps
• when [someone] oversleeps

In this sentence, と suggests a natural or predictable result:

• If you oversleep in the morning, you miss the train.

It sounds like a general consequence, not a one-time guess.

This is normal in Japanese.

Before と, the verb usually appears in its plain form:

• 寝坊する と

The main sentence can still be polite:

• 乗り遅れます

So the sentence mixes:

• plain form in the conditional clause
• polite form in the main clause

That is very common and natural.

Japanese often uses the dictionary/non-past form before conditionals like と.

So:

• 寝坊する does not only mean to oversleep
• in this structure, 寝坊すると means if/when [someone] oversleeps

Japanese conditionals do not work the same way as English tense. The non-past form is the normal form used here.

The verb 乗り遅れる means to miss (a train, bus, etc.) by being too late to board it.

With this verb, the vehicle is marked by に:

• 電車に乗り遅れる
• バスに乗り遅れる

This is because the expression is built from 乗る (to ride/get on), which also takes に:

• 電車に乗る = to get on the train

So に stays in the compound verb 乗り遅れる.

乗り遅れる is a compound verb:

• 乗る = to get on / ride
• 遅れる = to be late

Together, 乗り遅れる means:

• to miss a train/bus/etc. because you were too late to get on it

So it is not just any kind of missing. It specifically means:

• you were late
• and because of that, you failed to board

Japanese often leaves the subject unstated when it is clear from context.

So this sentence could mean:

• If I oversleep in the morning, I miss the train.
• If you oversleep in the morning, you miss the train.
• If people oversleep in the morning, they miss the train.

Without more context, it sounds like a general statement about what happens.

All three can relate to if, but they have different nuances.

Here, と works well because it expresses a regular consequence or automatic result:

• 朝寝坊すると、電車に乗り遅れます。
• If you oversleep in the morning, you miss the train.

This sounds like a general truth or habitual outcome.

By contrast:

• たら often sounds more like if/when that actually happens
• なら often means if that is the case / if you say so

So と is a natural choice when describing what usually happens as a result.

No, it is not grammatically required, but it is often used to make the sentence easier to read.

So both are possible:

• 朝寝坊すると、電車に乗り遅れます。
• 朝寝坊すると電車に乗り遅れます。

The comma simply helps separate the if-clause from the main result.

Yes, depending on context, 寝坊する can mean:

• to oversleep
• to sleep in
• to get up late

In this sentence, because the result is missing the train, it clearly has the sense of:

• oversleeping / getting up too late

So the nuance is not just relaxing and sleeping late for fun; it is sleeping late in a way that causes a problem.