Bij de kruising ga ik soms de verkeerde kant op als ik niet goed oplet.

Bij de kruising means at the intersection / when I get to the intersection.

Dutch often puts a time/place phrase first to set the scene. Starting with Bij de kruising makes the location the topic of the sentence.

A learner may expect Op de kruising, but bij is more natural here because it means at/near the intersection, not literally on top of it.

This is because Dutch main clauses usually follow the V2 rule: the finite verb must be in the second position.

If the sentence began with Ik, you would say:

Ik ga soms de verkeerde kant op ...

But because Bij de kruising comes first, the verb must come next:

Bij de kruising ga ik soms ...

So the subject ik moves after the verb.

Soms means sometimes.

In this sentence, it comes after the subject:

Bij de kruising ga ik soms de verkeerde kant op ...

That is a very normal position for adverbs like soms, vaak, nooit, and meestal.

You could think of the structure as:

place phrase + verb + subject + frequency adverb + rest

This is a very common Dutch directional expression.
de verkeerde kant op gaan means to go the wrong way.

The parts are:

• de verkeerde kant = the wrong direction / the wrong side
• op = in the direction of / onward

So Dutch expresses this idea literally as go the wrong direction on/up.

It is best learned as a chunk:

de goede kant op = the right way
de verkeerde kant op = the wrong way

Because Dutch often places directional particles later in the clause.

The verb here is basically opgaan in the sense of go in a certain direction, but in normal Dutch word order the particle is often separated:

• Ik ga de verkeerde kant op.
• Ga niet die kant op!

This kind of split is very common with Dutch separable verbs and verb-particle combinations.

Yes, very much so.

Dutch speakers commonly use:

• deze kant op = this way
• die kant op = that way
• de goede kant op = in the right direction
• de verkeerde kant op = in the wrong direction

So even though you can analyze the grammar, it is very useful to memorize de verkeerde kant op gaan as a whole expression.

Here als means if.

The clause als ik niet goed oplet gives the condition: if I’m not paying close attention.

In Dutch, als can often mean either if or when, depending on context.
In this sentence, if is the natural interpretation.

Because opletten is a separable verb.

In a normal main clause, the verb splits:

• Ik let goed op.
• Hij let niet op.

But in a subordinate clause introduced by als, the parts come back together:

• ... als ik niet goed oplet.

So:

• main clause: let ... op
• subordinate clause: oplet

This is one of the most important patterns in Dutch grammar.

Because in Dutch subordinate clauses, the verb usually goes to the end.

The clause is:

als ik niet goed oplet

That follows the common pattern:

subordinating conjunction + subject + other words + verb

Examples:

• omdat ik moe ben
• als hij komt
• terwijl wij eten

So oplet goes at the end because als starts a subordinate clause.

Because niet usually comes before the part it is negating.

Here, niet goed means not well / not properly.

So:

• goed opletten = to pay good attention / pay close attention
• niet goed opletten = not pay close attention

This is similar to English not properly paying attention.

Opletten means to pay attention, to be careful, or to watch out.

In this sentence, niet goed opletten means:

• not paying enough attention
• not being careful enough

It is a very common everyday verb.

Examples:

• Let op! = Watch out! / Pay attention!
• Je moet goed opletten. = You have to pay close attention.

Grammatically, wanneer usually means when, while als often means if or when.

In this sentence, als is better because the meaning is conditional: I go the wrong way if I don’t pay attention.

If you used wanneer, it would sound more like a time statement than a condition. So als is the more natural choice here.

In modern Dutch, a comma before a subordinate clause is often optional unless it helps clarity.

So both of these can be seen:

• Bij de kruising ga ik soms de verkeerde kant op als ik niet goed oplet.
• Bij de kruising ga ik soms de verkeerde kant op, als ik niet goed oplet.

The version without the comma is completely normal.

Yes, that is also grammatical.

Dutch is flexible about what comes first. Compare:

• Bij de kruising ga ik soms de verkeerde kant op ...
• Ik ga bij de kruising soms de verkeerde kant op ...

The first version emphasizes the location at the intersection.
The second starts more neutrally with I.

So the original sentence is not unusual; it just gives prominence to Bij de kruising.