Even if your intention is to help somebody, you must communicate your intent clearly — so as to not be misunderstood as a harasser.
Let’s face it — a car following a girl on a dark road is often harassment. When there’s not enough information, it is human tendency to assume the worst. And when you’re trying to help somebody, especially at a place like a dark road — please keep that in mind, you don’t want the person you’re helping to start panicking and over speeding, in an attempt to get away.
