A car is almost essential in the Lake District; bus service is limited and trains can get you to the edge of the national park but no farther. You can rent cars in Penrith and Kendal. Roads within the region are generally good, although minor routes and mountain passes can be steep and narrow. Warning signs are often posted if snow or ice has made a road impassable; check local weather forecasts in winter before heading out. In July and August and during the long public holiday weekends, expect heavy traffic. The Lake District has plenty of parking lots; use them to avoid blocking narrow lanes. Most parking lots require payment; it's smart to keep some change on hand.
To reach the Lake District by car from London, take M1 north to M6, getting off either at Junction 36 and joining A590/A591 west (around the Kendal bypass to Windermere) or at Junction 40, joining A66 direct to Keswick and the northern lakes region. Travel time to Kendal is about four to five hours, to Keswick five to six hours. Expect heavy traffic out of London on weekends.