I have done quite a lot of driving, both professionally, doing weddings in the area for the owner of two set ups and years ago for a farmer with a loopy, coloured driving pony who he became frightened of due to his habit of running away while in harness! He was rather keen, but I weighed his 4 wheel flat bed cart down with as many humans I could muster and that slowed him down a lot! I drove along main roads, country lanes and right into the city of Bath, waiting for brides outside churches and outside the Pump Rooms in front of Bath Abbey, surrounded by swarms of Japanese tourists ten deep. Gerry was a really marvellous driving horse - he was a 16hh chestnut cob gelding and he had a Victoria 4 wheel carriage, which seats four, plus the driver and groom. Bill was the other horse who was used commercially for driving and he also pulled a Victoria. He was a bit fast and took a lot of holding at times but he looked very impressive as he was a smart welsh section D and was jet black.
I broke my 12:3hh palomino pony, Sunny Boy to harness about 8 years ago and I now use him to harrow the school every week but I don't have a cart for him at present. He finds it hard work too as the sand drags up and makes the harrow pretty heavy. Dont under-estimate the effort needed to pull anything without wheels.
The best way is to have had some lessons from an expert and get the pony/cart/harness/road safety issues understood. Double check that your pony really is 100% in ALL traffic, because if he is not absolutely bomb proof don't break him to drive him at all as the car drivers are often highly inconsiderate towards driving horses and ponies to say the least.
So, with that established, the first thing is to long rein him - a lot - practice turning left and right, trotting and walking and make sure he understands 'whoa' and 'stand' before finding a well fitting harness, with a well fitting blinker bridle. Then you need to long rein him in the blinker bridle and harness to accustom him to that lot - the crupper can cause alarm for some horses at first, but this often is short lived. If this is all going well and with no hang ups, you will now be ready to introducing some 'weight' for him to drag in a safe enclosed area - a tyre works well, have a friend with you from now on and get the friend to attach the tyre to the traces with some easy to cut bailing twine and I also use a a quick release clip too, but carrying a flick knife to cut harness at all times is essential in case of emergencies. Be very careful not to let the traces drop too low as they hang by his sides towards the tyre as he may get his hind leg over them and get in a muddle. When I am arena levelling and therefore dragging an object, rather than pulling a wheeled cart, I take the traces through the shaft tugs and also through the buckled up breeching straps to keep them nice and high up. Really all driving horses need to become accustomed to getting in a muddle with lines or such like going anywhere though, to prepare them for if it happens by accident. I drape detatched lunge reins or driving lines over their bodies and wrap them under their tummies to accustom them to this. I reward with food treats for good behaviour and calmness and never rush. Once they are accustomed to dragging a tyre, progress to two tyres to make a greater weight to pull, but dont over face the pony as he will probably refuse to pull at all if its too heavy.
As for the carts and carriages, I personally prefer a cart that has some simple braking system on it - its nice to have brakes to help the horse or pony out when going downhill, as otherwise they have to sit on the breaching to stop the cart pushing them forwards but many of the cheap exercise carts don't have any brake system at all fitted. It is possible to have someone come out and make a cart to suit you and your pony, which is a lovely way to ensure it is balanced right and fits nicely. Four wheelers are easy to use and the balance is not so totally critical for the horse or pony as four wheelers do not put any weight onto the animals back - as a two wheeler does.
In my experience the driving community is a friendly one, but many of the old fashioned ones like I learned with are a very different sort from the riding people I know now! LOL! I am not prepared to say why though!
