kono reen ha nagai.

In this sentence, は is the topic particle, and when は is used as a particle, it is pronounced wa, not ha.

So:

• この レーン は 長い。
• is read kono rēn wa nagai

This is a very common point for beginners. The writing stays は, but the pronunciation changes to wa only in this grammatical use.

この means this, but it must be followed by a noun.

So:

• この レーン = this lane

This is different from:

• これ = this one / this

A useful comparison:

• これ = this
• この + noun = this + noun

So you can say:

• これは長い。 = This is long.
• このレーンは長い。 = This lane is long.

レーン is a loanword, borrowed from English lane, so it is written in katakana, which is often used for:

• foreign loanwords
• foreign names
• some sound effects
• emphasis in some cases

So レーン is just the Japanese katakana version of lane.

は marks the topic of the sentence.

Here, the topic is:

• このレーン = this lane

So the sentence is structured like:

• As for this lane, it is long.

That is why Japanese learners often translate は loosely as as for.

In natural English, we usually just say:

• This lane is long.

But grammatically, Japanese is often organizing the sentence by topic first.

Japanese does not always need a separate word for is in sentences with i-adjectives like 長い.

Here:

• 長い already means is long / long

So:

• このレーンは長い。 literally works as
• As for this lane, [it] is long.

This is very different from English, where you need is.

A related example:

• この道は長い。 = This road is long.
• その映画は面白い。 = That movie is interesting.

No separate is is needed there either.

長い is an i-adjective.

Japanese adjectives are often divided into two major groups:

• i-adjectives
• na-adjectives

長い ends in い, so it is an i-adjective.
That matters because i-adjectives can directly end a sentence:

• 長い。 = It is long.

So in your sentence:

• このレーンは長い。

the adjective itself functions as the predicate.

Because 長い is the plain dictionary form of the adjective and is the correct form for ending this sentence.

• 長い = long / is long

By contrast:

• 長く is an adverb-like or connecting form, used in other structures
  
  • for example: 長くない = not long
• 長です is incorrect because 長い is an i-adjective, so you do not attach です directly to the stem 長

The polite version is:

• このレーンは長いです。

not:

• このレーンは長です。

Sometimes, but the nuance changes.

• このレーンは長い。
  = As for this lane, it is long.

• このレーンが長い。
  = This lane is the one that is long / This lane is long (with more focus or contrast depending on context)

Very roughly:

• は often marks the topic
• が often marks the subject with stronger focus or identification

For a beginner, は is the most neutral choice here if you are simply describing this lane.

Japanese sentence order is very different from English. Japanese often places the main predicate at the end.

So:

• このレーン = this lane
• は = topic marker
• 長い = is long / long

This follows a very normal Japanese pattern:

• [topic] は [description]

Examples:

• この本は面白い。 = This book is interesting.
• その山は高い。 = That mountain is tall/high.

So the word order may feel backward from English, but it is completely normal in Japanese.

このレーンは長い。 is in the plain style.

It is not rude by itself, but it is less formal than the polite form.
The polite version would be:

• このレーンは長いです。

So:

• 長い。 = plain
• 長いです。 = polite

You would often hear the plain form in casual conversation, narration, or textbook examples.

You are right: normal Japanese is usually written without spaces.

So the sentence would normally appear as:

• このレーンは長い。

Spaces are often added in beginner materials to make it easier to see the parts of the sentence.

So this:

• この　レーン　は　長い。

is just a learner-friendly version of:

• このレーンは長い。

No, that would sound unnatural here.

If you want to say this lane, use:

• このレーン

not:

• これのレーン

That is because この is the form that directly modifies a noun.

Use:

• これ = this
• この + noun = this + noun

So:

• このレーン = this lane

is the correct form.

In this sentence, yes, it most naturally means physical length: the lane is long.

But 長い can also be used in other ways depending on context, such as:

• 時間が長い = the time is long
• 髪が長い = hair is long

So the core idea is long, but the exact nuance depends on what is being described. Here, with レーン, physical length is the natural interpretation.