Per colpa del traffico, arrivo tardi in ufficio.

Yes, per colpa di is used when the cause is seen as negative, blameworthy, or unfortunate.

In this sentence, Per colpa del traffico suggests:

• the traffic is the problem
• the speaker is annoyed by it
• the traffic is what caused the lateness

So it is stronger than a neutral because of.

A useful comparison:

• per colpa del traffico = because of the traffic / thanks to the traffic in a clearly negative sense
• a causa del traffico = due to the traffic, more neutral or formal

So per colpa di is very common when something bad happens and you want to assign blame.

Del is a contraction of di + il.

So:

• di + il = del
• per colpa di il traffico becomes per colpa del traffico

This is just the normal Italian way of combining a preposition and a definite article.

Some related forms:

• di + lo = dello
• di + la = della
• di + i = dei
• di + gli = degli
• di + le = delle

So del traffico literally comes from of the traffic, even though in English we would normally say because of traffic or because of the traffic, depending on context.

Italian usually drops subject pronouns when they are not needed.

So:

• arrivo already means I arrive / I’m arriving
• the ending -o tells you the subject is I

Because of that, io is often omitted.

You would only add io if you want emphasis or contrast, for example:

• Io arrivo tardi, ma tu sei puntuale.
  I arrive late, but you are punctual.

In your sentence, plain arrivo is the most natural choice.

In Italian, the present tense can be used in several ways, just like in English depending on context.

Here arrivo tardi in ufficio can mean things like:

• I arrive late at the office
• I’m arriving late at the office
• I get to the office late

It can describe:

1. a habitual situation
   
   • Because of traffic, I arrive late at the office
2. something happening now or today
   
   • Because of traffic, I’m arriving late at the office

Without more context, both are possible.

Because tardi here is an adverb, not an adjective.

It modifies the verb arrivo, telling us how the speaker arrives:

• arrivo tardi = I arrive late

Compare:

• un treno in ritardo = a delayed train
• arrivo tardi = I arrive late

So tardi stays the same; it does not change for gender or number.

Both can often be translated as late, but they are used a little differently.

• arrivo tardi = I arrive late
• sono in ritardo = I am late

So:

• tardi is an adverb
• in ritardo is a fixed expression meaning late / behind schedule

Both are natural, but they are structured differently:

• Per colpa del traffico, arrivo tardi in ufficio.
• Per colpa del traffico, sono in ritardo per l’ufficio.
  or more naturally
• Per colpa del traffico, sono in ritardo.

In your sentence, arrivo tardi is perfectly idiomatic.

In ufficio usually means at the office or to the office in a general sense.

Italian often uses in with places like:

• in ufficio = at/to the office
• in banca = at/to the bank
• in ospedale = in/to the hospital

All’ufficio is possible in some contexts, but it usually sounds more like to the office / at the office as a specific destination or location, often with a more concrete sense.

In this sentence, in ufficio is the most natural way to say at the office.

The comma is natural, but not absolutely required in every context.

With the comma:

• Per colpa del traffico, arrivo tardi in ufficio.

This makes the opening cause phrase feel clearly separated from the main clause, much like English:

• Because of the traffic, I arrive late at the office.

Without the comma:

• Per colpa del traffico arrivo tardi in ufficio.

This is still understandable and acceptable, especially in less formal writing. The comma just improves readability and mirrors the pause a speaker might make.

Yes. A causa del traffico is correct and very common.

The difference is mainly tone:

• per colpa del traffico = more emotional, more blaming
• a causa del traffico = more neutral, more formal

So:

• Per colpa del traffico, arrivo tardi in ufficio.
  sounds like the speaker is annoyed
• A causa del traffico, arrivo tardi in ufficio.
  sounds more neutral and matter-of-fact

Both are correct; the choice depends on tone.

In principle, traffico can have different meanings depending on context, but in this sentence it is almost certainly road traffic.

That is because:

• arrivo tardi
• in ufficio
• per colpa del traffico

together strongly suggest commuting and congestion on the road.

So a learner should understand traffico here as traffic on the streets / traffic jams.

Yes. Italian allows some flexibility in word order.

For example:

• Arrivo tardi in ufficio per colpa del traffico.
• Per colpa del traffico, arrivo tardi in ufficio.

Both are correct.

The version with Per colpa del traffico first gives more emphasis to the cause. It sets up the reason before giving the main information.

That is very common in Italian, especially when the speaker wants to foreground the explanation.