Really anti-social behavior. Not just rude, but unsafe...the leaders are essentially encouraging those in the back to blow the red light with their "we're not waiting for you" routine. The decent thing to do is to say, in word or in deed, "don't take risks at the light, we'll let you catch up". I'd bring it up, but if you get any excuses or defensiveness, take it as a sign that they don't give a rats a** about you being on their ride.