yuuhodou de hansyazai wo tukau.

It is read:

ゆうほどう で はんしゃざい を つかう

Word by word:

• 遊歩道 = ゆうほどう
• で
• 反射材 = はんしゃざい
• を
• 使う = つかう

Here, で marks the place where an action happens.

So in this sentence, 遊歩道で means:

• on the promenade / on the walking path
• at the walkway
• more literally, in the place called the promenade, use ...

This is a very common use of で:

• 学校で勉強する = study at school
• 公園で遊ぶ = play in the park
• 遊歩道で使う = use it on the promenade

So で is not the object marker and not the destination marker here. It marks the location of the action.

を marks the direct object of the verb.

The verb is 使う, which means to use, and the thing being used is 反射材.

So:

• 反射材を使う = to use reflective material / reflectors

This is the standard pattern:

• 道具を使う = use a tool
• 日本語を使う = use Japanese
• 反射材を使う = use reflective material

Japanese often leaves out the subject when it is obvious from context or not important.

So 遊歩道で反射材を使う could mean different things depending on the situation, such as:

• Use reflective material on the promenade.
• People use reflective material on the promenade.
• I use reflective material on the promenade.
• You should use reflective material on the promenade.

In English, you usually need to choose a subject. In Japanese, leaving it unsaid is very normal.

反射材 literally means reflective material.

In real-life usage, it often refers to things such as:

• reflective strips
• reflectors
• reflective safety gear
• material that reflects light, especially for visibility at night

So depending on context, English might translate it more naturally as:

• reflective material
• reflective gear
• a reflector
• something reflective

The Japanese word itself is a bit broad.

使う is the dictionary/plain form.

This form can be used in several situations:

• casual speech
• written instructions
• notes or labels
• headlines
• neutral descriptions

So this sentence may sound like:

• a simple statement
• a heading
• a rule or instruction written briefly

If you wanted to make it more polite as a full sentence, you could say:

• 遊歩道で反射材を使います。

If you wanted a clearer instruction:

• 遊歩道では反射材を使ってください。 = Please use reflective material on the promenade.

Normally, で is the correct particle here.

Why? Because 使う is an action, and で marks the place where that action happens.

• 遊歩道で反射材を使う = use reflective material on the promenade

If you used に, it would usually sound unnatural here, because に often marks:

• destination
• existence
• time
• target/result in certain patterns

So:

• 公園で遊ぶ is natural
• 公園に遊ぶ is not natural

The same idea applies here. Since 使う is an action taking place at that location, で is the expected choice.

Most directly, it means use it there, with there being the promenade/walking path.

It does not by itself say:

• while walking
• at night
• for safety
• who is using it

Those ideas may be implied by context, but they are not stated in the grammar.

So 遊歩道で simply sets the location of the action.

Yes, it can be natural, but it sounds a bit context-dependent and somewhat brief.

By itself, it feels like one of these:

• a memo
• a short instruction
• a heading
• a rule in a safety guide

In everyday conversation, a fuller sentence might be more natural, such as:

• 遊歩道では反射材を使ってください。
  Please use reflective material on the promenade.

• 夜に遊歩道を歩くときは、反射材を使いましょう。
  When walking on the promenade at night, let’s use reflective material.

So the original sentence is not wrong, but it feels compact.

There does not have to be a は in every sentence.

This sentence focuses on the basic action structure:

• 遊歩道で = location
• 反射材を = object
• 使う = verb

If you add は, the nuance changes a little. For example:

• 遊歩道では反射材を使う。

This makes 遊歩道 more of a topic/contrast point, something like:

• As for on the promenade, use reflective material
• At least on the promenade, reflective material is used
• On the promenade, unlike elsewhere, use reflective material

So the version without は is a simpler, more neutral statement.

The spaces are just for learner readability.

Normal Japanese writing would usually be:

遊歩道で反射材を使う。

Japanese does not normally put spaces between words the way English does.

Learning materials often add spaces to help beginners see:

• where one word ends
• which part is a particle
• how the sentence is built

So the spaced version is a teaching aid, not standard spelling.