Same thing happened to me the first time I harnessed up and drove my mini mare. I'd trained and driven my quarter horse, so I figure it would be a breeze. Oh my gosh, was it scary.
The person who sold me her, told me minis dont need breeching, so even though I had one, I didn't put it on. Well the cart touch her back legs and we started galloping down the paved road as fast as she could manage. I have always been of the opinion that you stay with your horse, as they could come to real danger all alone with a cart flying after them. She ran like this for a half a mile or so, luckily no traffic came by or we'd have been killed, I'm sure. I thought she might run herself out, but when she saw a driveway she bolted into it and missed it completely as we were going way too fast to make it. We were both upside down in the ditch when I came to. Wasnt' out long as she was still struggling to get up, but couldn't.
I got the harness taken off her (I didn't have a knife). Got her out of the ditch and pulled the cart up. Hard to believe the only thing that was damaged of the equiptment was the detailing and a small amount of paint on the cart. But she lost her foal after this and I'll always have a bad hip. Needless to say, when we go driving now a days we wear the breeching and have never had an incident again.
I also reharnessed and drove her home, as I had no way to get my wounded hip, cart and horse home if I didn't.
Amazing what we can survive.
The accident sounds terrible.
OH! Breed them, the geld them, then drive them. Glad to hear you are both okay, but I just cringed when I read you saying the cart shafts snapped. Carts aren't cheap.
