Preheat the oven to 400°F (200°C) and line a heavy-duty rimmed baking sheet with parchment paper.
In a large stainless steel mixing bowl, combine the carrots, parsnips, sweet potato, and red onion wedges.
Emulsify the olive oil, salt, pepper, rosemary, and thyme, then pour over the vegetable medley.
Toss the ingredients thoroughly until each piece is uniformly coated with the oil and herb mixture.
Distribute the vegetables across the prepared baking sheet in a single layer, ensuring sufficient headspace between pieces to prevent steaming.
Transfer the sheet to the center rack of the oven and roast for 45 minutes.
At the 20-minute mark, use a flat spatula to turn the vegetables to ensure even caramelization on all surfaces.
Verify tenderness with a paring knife; the vegetables should be soft in the center with charred, golden-brown edges.
Remove from the oven and rest for 5 minutes before service to allow the sugars to set.