Position the Rack in the center of the oven and preheat the oven to 400 degrees F. In a large bowl, toss the carrots, parsnips, Brussels sprouts, sweet potato, oil, and herbs with 2 teaspoons each of kosher salt and pepper to coat. Arrange the vegetables evenly on a large, heavy baking sheet. Roast the vegetables until tender and golden, stirring occasionally, about 35 minutes. Season with more salt and pepper to taste. (The vegetables can be made up to 4 hours ahead. Rewarm in the oven before serving.) Transfer the vegetables to a platter and serve.