Learn Finnish: Insinööri tutkii uusia liikennevaloja. - The engineer is examining new traffic lights.

The verb tutkia (to examine or study) is a partitive verb, meaning its object must always be in the partitive case. Because the engineer is examining multiple traffic lights, the entire object phrase must be in the partitive plural.

Why is the word for 'new' uusia here? Doesn't the partitive of uusi usually end in '-tta'?

You are thinking of the partitive singular form, which is uutta. Because liikennevaloja is plural, the describing adjective must match it and take the partitive plural form, which is uusia.

How do we build the partitive plural liikennevaloja from the basic dictionary word?

The basic word is liikennevalo. For most words ending in a single -o or -ö, you form the partitive plural simply by adding -ja or -jä to the end. That gives us liikennevaloja.

Does tutkii mean 'examines' or 'is examining'?

It can mean both! Finnish does not have a separate continuous tense like English does with 'is doing'. You can translate it as a general habit or an ongoing action depending on the context.