Pre-heat the oven to 425 degrees F. Position a rack in the bottom third of oven and another rack in center of the oven. Combine all the cut vegetables, rosemary, thyme and olive oil in a large bowl and toss to coat. Season with salt and pepper. Divide the vegetables between two heavy rimmed roasting trays or baking sheets. Roast the trays of vegetables for 30 minutes, stirring occasionally. Reverse the positions of the baking sheets halfway through the baking time, for even cooking.