/* CMD_TERRAFORM_LAND may append further items to _cleared_object_areas,

		 * however it will never erase or re-order existing items.

		 * _cleared_object_areas is a value-type SmallVector, therefore appending items

		 * may result in a backing-store re-allocation, which would invalidate the coa pointer.

		 * The index of the coa pointer into the _cleared_object_areas vector remains valid,

		 * and can be used safely after the CMD_TERRAFORM_LAND operation.

		 * Deliberately clear the coa pointer to avoid leaving dangling pointers which could

		 * inadvertently be dereferenced.

		 */

		assert(coa >= _cleared_object_areas.Begin() && coa < _cleared_object_areas.End());

		size_t coa_index = coa - _cleared_object_areas.Begin();

		coa = NULL;

		ret = DoCommand(end_tile, end_tileh & start_tileh, 0, flags, CMD_TERRAFORM_LAND);

		if (ret.Failed()) return_cmd_error(STR_ERROR_UNABLE_TO_EXCAVATE_LAND);

		cost.AddCost(ret);

	}

	cost.AddCost(_price[PR_BUILD_TUNNEL]);

	/* Pay for the rail/road in the tunnel including entrances */

	switch (transport_type) {

		case TRANSPORT_ROAD: cost.AddCost((tiles + 2) * _price[PR_BUILD_ROAD] * 2); break;

		case TRANSPORT_RAIL: cost.AddCost((tiles + 2) * RailBuildCost(railtype)); break;

		default: NOT_REACHED();

	}