My daughter drives too close to vehicles in front. How do I tell her this behaviour is dangerous?

‘Unfortunately, when a habit like this is ingrained, you do actually have to draw someone’s attention to it for it to change.’ Painting: A Woman and a Girl Driving (1881) by Mary Cassatt. Photograph: Mary Cassatt/Alamy

Please can you help me with finding a way to tell my daughter that her driving is dangerous? She drives incredibly close to the back of the vehicle in front. It is difficult to judge, but it sometimes feels like we are no more than a couple of metres away, while we are driving very fast.

We live near lots of major roads and motorways, so trips will usually involve this type of road. I am not a nervous driver/passenger and if it wasn’t so dangerously close, I’d possibly be able to live with it. She has two young children and a husband whose driving she thinks is bad, as he is so fast.