Who Does the -des Action

The des-form (minnes, lugedes, süües) does not show who does the action. The reader understands that the subject of the main verb does it:

• Koju minnes kohtasin sõpra. (I met a friend on my way home. I was going home.)
• Raamatut lugedes jäi ta magama. (She fell asleep while reading the book. She was reading.)

So check the subject. In Tänavat ületades sõitis mulle auto otsa, the subject is auto, so the sentence says that the car was crossing the street. Careful writing avoids this. Say instead: Kui ma tänavat ületasin, sõitis mulle auto otsa. (A car hit me while I was crossing the street.)

When someone else does the -des action, you can name them in the genitive before the des-form. This works mainly with verbs that take no object:

• Päikese tõustes olime juba teel. (When the sun rose, we were already on our way.)
• Laste magades koristasime köögi. (While the children slept, we cleaned the kitchen.)

Some fixed phrases are always correct: ausalt öeldes (to be honest), minu arvates (in my opinion), minu nähes (while I watched), and words like võrreldes (compared with) and alates (starting from).

In speech, and when the context makes the doer obvious, you will also hear des-forms without a matching subject. In careful writing, it is safest to keep the same subject or use a clause.