There are several different ways to transport a trike when all you have to use is a car. Here are some examples:
If your car trunk is large enough and if you have a folding trike that folds small enough AND IF YOU ARE STRONG ENOUGH than you can go the route of lifting the trike in and out of the trunk. (That doesn’t appeal to me.) And as you can see in the picture below it is most likely damage would occur to the car interior as well as the trike. No way would I do this to a vehicle unless is was a “junker” I didn’t care about. (Yes, this is a picture of a SUV or van, not a car.)
If the vehicle happens to be one which will accommodate hauling a trike inside by putting it in backwards (and possibly having to lower or remove the seat or anything else which might be too high) you might have an easier time of hauling it than trying to put it in the trunk. Here is a TerraTrike inside a Camaro. A guy I know hauls a TerraTrike inside a new Toyota Prius 5. Again, if I were to do this I would want to be very certain nothing can and does go wrong resulting in messing up the car. That might mean placing cardboard or something in position to prevent contact with seats, etc.
As you can see the dimensions of this cargo carrier  below would require a tadpole trike to be folded to fit on it. The ramp is hinged so once the trike would be loaded the ramp swings up and locks vertically. Of course, this requires a receiver type trailer hitch. These are noisy going down the road as they bounce around and rattle. A trike would definitely need to be fastened down or it would get tossed out.
This vertical haul is accomplished using a bike carrier. I would want to be sure the rear tire or any other part of the trike isn’t in contact with the exterior surface of the vehicle.
And this horizontal haul also is using a bike carrier. I personally don’t care for this for two reasons … too difficult to lift trike up there and the trike would mess up the exterior of the vehicle unless caution and measures were taken to prevent it.
This vertical haul uses a receiver type hitch and trike rack. I definitely much prefer this over the ones above where a trunk mounted bike rack are used.
This I find most appealing of all the systems … a receiver type hitch with a trike carrier which tips down for loading and unloading. This would be the easiest to use. One could have a non tip down rack which is low to the ground making it easy to load and unload, but then if you were to drive certain places the rack could hit and drag on the ground. This tip down rack is fairly high off of the ground when brought back up to the hauling/traveling position. As long as I was able to lift the trike up onto the rack I would leave it up and not use the tip down feature when loading it. Perhaps I would leave it up to unload it too as it isn’t all that high of a lift.
Some people transport their trikes with little more than straps to hold it down. They lift the trike up onto the trunk and roll it on up onto the roof. Some leave the end of the trike on the trunk or rear window while others put the entire trike up on the roof. Again, I don’t think much of this system … not if you have a vehicle you care about as this would really mess it up in time. Of course, if there is an air foil (spoiler) on the rear of the trunk to contend with it would complicate things. (Yeah, I know … this is a picture of a Delta trike and not a Tadpole trike.) If I were going to go this route I would either want another person to help get the trike safely up and down without damaging the car or trike. Otherwise I would want ramps to load it up onto the top. It would probably be best to have both. 🙂
As thin as the metal in cars is I would be quite concerned about it getting dented in by having the trike sit on it like this.
Of course, one can make their own carriers/racks if they have the ability, equipment, facilities and materials. Here is an example of one:
I didn’t deal with the obvious … pick up trucks, vans, trailers, etc. Whatever means you use to haul a tadpole trike or if you always just ride it from home and don’t ever haul it … may we all …
KEEP ON TRIKIN’
Tadpole Rider 