I bought this whistle from Galls 16+ years ago and it is a staple tied onto my traffic vest. The rubber cushioning has long since worn off, but nothing beats that Fox40 sound. This whistle has gotten many inattentive drivers' attention and works flawlessly.
Not sure how the other reviewers said it's too quiet and ineffective. Maybe they're blowing into the wrong end?
Either way, if you're looking for a whistle to use directing traffic, this is the only one you'll need for years.