I THINK of my car's indicators as an alternative to my voice. In the same way that you would not speak without thinking first, so you should not signal automatically without considering how the message will be interpreted.

I remember telling this to a pupil who hardly ever spoke to me because English was not her first language. Although the analogy wasn't really appropriate for her, she got the picture.

One day we were practising her junction routine in Cressex and as we turned left out of a T-junction I saw two old ladies on the right pavement waiting to cross the road just beyond a turning on the right.

After straightening up, Mrs Learner tried to manually cancel the indicator but accidentally flashed the right signal before finding the correct position. The old ladies saw the right signal, assumed we turning into the road before them and stepped out in front of us.

"Stop!" I told Mrs Learner.

We were only doing about five miles an hour so she stopped immediately, but she was slow to put the clutch down and we stalled to a jerky halt. The old ladies looked up and clutched each other in fright, no doubt shocked that we hadn't turned off as they expected.

I gesticulated an apology and they stomped off down a footpath that cut through the estate.

After discussing the situation with Mrs Learner, we continued around the block and when we rounded the next bend, we saw the old ladies waiting to cross the road again.

"There are those old ladies again. Are you going to run them over properly this time?" I joked.

Unfortunately, Mrs Learner's grasp of English did not stretch to appreciating the subtleties of irony. She gorped at me and said: "You want I to hit them?!"

"No-o-o I'm joking! Just keep going," I said, hardly able to get my words out quickly enough.

As we cruised past the old ladies we smiled gracefully and they returned the gesture, blissfully unaware that we had just been discussing their early demise.

The sobering moral of this story is that had we been going faster at the time of the incorrect signal, their demise could have been a reality, not a joke. It only takes a second for a wrong signal to lead to disaster because others make their decisions based on what your indicators tell them.

Even leaving a signal on for too long could easily cause a crash. I'm sure there have been many times when you have reached the end of a road, seen car coming from the right signalling to turn into your road and been ready to pull out, only to watch it pass you with its left indicator still flashing.

Another common error is when motorists signal automatically without first checking their mirrors to confirm it is safe to change direction. Sometimes I play a game with my pupils where I make a ridiculous noise every time they do this. Why not play it next time you are out with an obliging passenger? It's a stupid bit of fun but it might just help you to think before you wink.