Vai dritto fino al ponte.

It is normally understood as a command/instruction here.

The form vai can also be the ordinary present tense you go, but in the context of giving directions, Italian uses it as an informal singular imperative: Go straight until the bridge.

So the context tells you how to read it.

Vai is the second-person singular form of andare.

Here it is being used for tu, so it is what you would say to:

• one friend
• one child
• one person you address informally

In other words, it is the informal singular command form in this sentence.

Italian usually leaves out subject pronouns when they are already clear from the verb form.

So instead of saying Tu vai dritto fino al ponte, Italian normally just says Vai dritto fino al ponte.

Adding tu is possible, but it would usually add emphasis, contrast, or impatience:

• Tu vai dritto, io giro a sinistra.
• Tu vai dritto!

Yes. Va' and vai can both be used for the informal command of andare.

A few notes:

• vai is extremely common in everyday speech
• va' is also correct and very common, especially in traditional grammar and before attached pronouns

For example:

• Vai dritto
• Va' dritto
• Vacci! = Go there!

So if you see either vai or va', do not be surprised.

Here dritto functions like an adverbial expression, meaning straight or straight ahead.

It does not mean that someone is physically straight in an adjective sense. Instead, it describes how you should go.

So:

• vai dritto = go straight
• cammina dritto = walk straight

In this use, learners can think of dritto as behaving like an adverb.

Usually, in this kind of direction-giving expression, learners will most often meet it as dritto.

Examples:

• Vai dritto
• Andate dritto
• Prosegua dritto

In everyday Italian, some variation can occur in related structures, but for directions, treating dritto as the fixed form you use after verbs like andare or proseguire is a very good rule.

Yes, in this context they can mean the same thing.

Both dritto and diritto can mean:

• straight
• upright
• direct

But dritto is very common in everyday spoken Italian, especially in directions:

• Vai dritto
• Sempre dritto

You may hear or read diritto too, but dritto is extremely natural here.

Because fino is normally followed by a when you indicate an endpoint, and a + il contracts to al.

So:

• fino a il ponte becomes fino al ponte

This is a normal Italian contraction:

• a + il = al
• a + la = alla
• a + lo = allo
• a + l' = all'
• a + i = ai
• a + gli = agli
• a + le = alle

So fino al ponte is the natural form.

Because in Italian, when you refer to a specific noun after a preposition like a, you often use the definite article.

So:

• ponte = bridge
• il ponte = the bridge
• al ponte = to the bridge / at the bridge / until the bridge, depending on context

In this sentence, fino al ponte means up to that specific bridge that serves as the landmark.

You change the verb form.

Common versions are:

• Vai dritto fino al ponte.
  informal, singular

• Vada dritto fino al ponte.
  polite/formal, singular

• Andate dritto fino al ponte.
  informal, plural

• Vadano dritto fino al ponte.
  formal, plural

The most useful contrast for learners is usually:

• vai = informal singular
• vada = polite singular

A simple pronunciation guide is:

• vai = sounds roughly like v-eye
• dritto = DRIT-toh, with a clear doubled tt
• fino = FEE-noh
• al = ahl
• ponte = PON-teh

Stress:

• vai
• DRIT-to
• FI-no
• PON-te

A rough full reading: v-eye DRIT-toh FEE-noh ahl PON-teh

Yes. Sempre dritto is also very common in directions.

Compare:

• Vai dritto fino al ponte.
• Vai sempre dritto fino al ponte.

Adding sempre makes it feel a bit more like keep going straight or continue straight on.

Both are natural, but sempre dritto can sound slightly more explicit in spoken directions.