Learn French: Le piéton traversant la rue est mon frère. - The pedestrian crossing the street is my brother.

Traversant is the present participle of traverser (to cross). In this sentence, it replaces a relative clause. Instead of saying Le piéton qui traverse la rue (The pedestrian who is crossing the street), we use the participle traversant to make the sentence more concise.

If the sentence was about multiple pedestrians, would traversant need an -s at the end?

No, it wouldn't change. When a present participle is used as a verb to replace a relative clause, it is invariable. This means it never changes form to match the noun. Even if the sentence started with Les piétons, the word would still be traversant.

Why isn't there an en before traversant?

You only use en before a present participle (forming what is called the gerund, like en traversant) when you mean 'while crossing' or 'by crossing' to describe how or when the main action happens. Here, we are just identifying the pedestrian, so we use the participle alone without en.

Is it more common to use traversant or qui traverse in everyday French?

In casual, everyday spoken French, you will hear qui traverse much more often. Using the present participle traversant to replace a relative clause is completely correct, but it is mostly found in formal writing, news reports, or literature.