شرطة المرور في موقع الحادث.

In Arabic, a present-tense sentence often does not use a word for is/are.

So شرطة المرور في موقع الحادث literally looks like:

• Traffic police
• at the site of the accident

But it naturally means:

• The traffic police are at the accident site

This is called a nominal sentence. In the present tense, Arabic usually leaves out to be.

If you wanted the past tense, then you would add a verb, for example:

• كانت شرطة المرور في موقع الحادث = The traffic police were at the accident site

Because شرطة المرور is an iḍāfa construction, often called a possessive or noun-link construction.

It literally means:

• شرطة = police
• المرور = traffic

Together:

• شرطة المرور = traffic police
  literally: the police of traffic

In an iḍāfa:

• the first noun usually does not take ال
• the second noun can be definite with ال

So:

• شرطة المرور is correct
• الشرطة المرور is not correct for this structure

Also, because the second word is definite, the whole phrase becomes definite: the traffic police.

المرور comes from a root connected with passing, movement, traffic.

In everyday Modern Standard Arabic, المرور often refers to:

• traffic
• traffic control
• things related to roads and vehicles

So شرطة المرور is the standard way to say:

• traffic police

You may also see related expressions like:

• إدارة المرور = traffic department
• قوانين المرور = traffic laws
• شرطي مرور = traffic policeman / traffic officer

This is another iḍāfa construction.

• موقع = site / location
• الحادث = the accident

So:

• موقع الحادث = the site of the accident
  or more naturally, the accident site

In an iḍāfa, the first noun usually:

• does not take ال
• gets its definiteness from the second noun

So:

• موقع الحادث = correct
• الموقع الحادث = not the right structure for this meaning

This pattern is extremely common in Arabic:

• باب البيت = the door of the house
• مدير المدرسة = the principal of the school
• مكان الحادث = the place of the accident

في is the preposition meaning in or at.

Here it introduces the location:

• في موقع الحادث = at the accident site

Arabic often uses في in places where English may say either in or at, depending on what sounds natural in English.

After في, the following noun is in the genitive case. In fully vocalized Arabic, that affects the ending:

• في موقعِ الحادثِ

But in normal everyday writing, those short vowel endings are usually not written.

شرطة is a bit tricky for English speakers.

It refers to the police, which is a collective idea. In English, police is plural in meaning, but in Arabic شرطة is treated as a singular collective noun.

So grammatically, it often behaves like a feminine singular noun.

For example, you may see agreement like:

• وصلت الشرطة = the police arrived

Here, the verb can be feminine singular because شرطة is grammatically singular feminine.

In your sentence, there is no verb, so you do not see that agreement directly.

Both words can relate to an incident or accident, but they are not always used in exactly the same way.

• حادث often means accident or incident, especially in news and official language
• حادثة can also mean incident or accident, but usage depends on context

In news-style Arabic, الحادث is very common for the accident:

• موقع الحادث = the accident site
• ضحايا الحادث = the victims of the accident

So this sentence sounds natural and standard.

A careful full pronunciation would be:

shurṭatu l-murūri fī mawqiʿi l-ḥādithi

Word by word:

• شُرْطَةُ = shurṭatu
• الْمُرُورِ = al-murūri / after connection, often heard as l-murūri
• فِي = fī
• مَوْقِعِ = mawqiʿi
• الْحَادِثِ = al-ḥādithi

In normal speech, especially in pause, some final case vowels may not be fully pronounced.

It can be understood as both, but it sounds especially natural as a headline, news caption, or photo caption.

Arabic news style often uses short nominal expressions like this:

• شرطة المرور في موقع الحادث
• رجال الإسعاف في المكان
• الدفاع المدني في موقع الحريق

This style is compact and very common in journalism. In fuller prose, you might also see something like:

• توجد شرطة المرور في موقع الحادث = The traffic police are at the accident site

But the shorter version is completely natural, especially in news contexts.