kono miti ha mizikaku, sikamo anzen desu.

短い is an い-adjective. When an い-adjective connects to another description, its final い can change to く.

So:

• 短い道 = a short road
• 道は短く、安全です = the road is short, and safe

In this sentence, 短く links 短い to the next predicate, 安全です.

A very common alternative is 短くて:

• この道は短くて、安全です。

That sounds a bit more conversational.
The 短く、しかも安全です pattern feels a little more written or carefully stated.

しかも means something like:

• moreover
• furthermore
• what’s more
• on top of that

It does more than just add another fact. It often adds a second point that strengthens the statement.

So the sentence is not just saying:

• This road is short and safe.

It is more like:

• This road is short, and what’s more, it’s safe.

That extra nuance is why しかも is useful here.

安全 is a な-adjective.

With a noun, a な-adjective uses な:

• 安全な道 = a safe road

But when it is at the end of a sentence, it does not use な:

• この道は安全です。 = This road is safe.

So:

• before a noun: 安全な
• at the end of a sentence: 安全です / 安全だ

That is why 安全なです is incorrect.

In Japanese, when descriptions are linked together, you usually do not repeat です after each one.

English often says:

• This road is short, and it is safe.

Japanese usually puts the final tense/politeness marking only at the end:

• この道は短く、しかも安全です。

The earlier part, 短く, is just a linking form.
The final です covers the sentence as a whole.

は marks the topic of the sentence.

So この道は means something like:

• As for this road...
• This road...

Then the sentence says something about that topic:

• it is short
• and moreover safe

A natural breakdown is:

• この道は = as for this road
• 短く、しかも安全です = is short, and moreover safe

English does not have a direct equivalent of topic marking, so は can take some getting used to.

Good question. 道 can mean:

• road
• street
• path
• route
• way

In a sentence like this, route or way may sound more natural in English than road.

So depending on context, the meaning could be closer to:

• This route is short and safe.
• This way is short and safe.

Japanese 道 is broader than the English word road.

The comma 、 helps separate the first description from しかも安全です.

Japanese commas are more flexible than English commas, but here the comma is very natural because it makes the structure easier to read:

• この道は短く、しかも安全です。

It shows a pause, almost like:

• This road is short, and moreover, safe.

So the comma is not just decoration; it helps the sentence flow clearly.

Yes, you could.

• この道は短くて、しかも安全です。

This is grammatical and natural.

The difference is mainly one of style and rhythm:

• 短くて is very common in everyday speech
• 短く、しかも... can sound a bit more formal, written, or neatly structured

Both mean essentially the same thing here.

Yes. The sentence ends with です, so it is in a polite style.

• この道は短く、しかも安全です。 = polite
• この道は短く、しかも安全だ。 = plain style

The polite version is appropriate in normal conversation, explanations, directions, or written informational Japanese.

No. Normal Japanese writing usually does not put spaces between words.

The standard writing would be:

• この道は短く、しかも安全です。

Spaces are often added only in beginner materials to make the sentence easier to read.

So the spaced version is for learning, not standard native writing.