Perhaps it is time for a bit of empirical evidence. According to a study by the Society of Automotive Engineers (SAE) International,
- Drivers neglect to use their turn signals approximately 750 billion times per year.
- Drivers neglect to use their turn signal 25% of the time when making a turn.
- Drivers neglect to use their turn signal 48% of the time while changing lanes.
- Drivers neglect to turn off their turn signals 48% of the time after changing lanes.
When people don’t use their turn signals, they are contributing to an environment in which other drivers have less control. A turn signal isn’t just a signal, it’s a warning. The use of a turn signal allows other drivers to notice the change in their surroundings and react appropriately. And if they’re decent people, they’re likely to react in a way that benefits your own safety, perhaps by giving you adequate space to change lanes on a busy highway.
Because of this behavior, the study concluded that the number of yearly car crashes in the U.S. that can be attributed to this issue is approximately two million, more than double the amount of crashes that are a result of distracted driving (950,000). This means that nearly 20% of all crashes in the U.S. occurred because one or more drivers failed to alert other drivers to an upcoming turn or lane change.
The BuzzFeed hammered reasons for signaling here: https://www.buzzfeed.com/daves4/turn-signals