A walking cast is different than one that requires the patient to use crutches in order to be mobile while the leg is recovering. It is supportive enough to alleviate pressure away from the injury so that the wearer is able to walk while the leg is still in a cast. This allows for a freer range of motion while the patient recovers, but it has its limitations. Therefore, the question of whether or not to drive becomes more of an ethical question as opposed to what the patient can physically do.
Determine Your Level of Comfort
There is no law prohibiting patients in a walking cast from getting behind the wheel of their own car, however, one must strongly and truthfully consider their level of comfort before getting behind the wheel. Ask yourself if your response time would be slowed. Can you comfortably manoeuvre all pedals with your cast on? Does the cast keep you from being able to do any of the basic motions required to safely operate a vehicle? If you answer negatively to any of these questions, then you should not drive with a cast on.
Getting Into an Accident
Should you deem yourself worthy to drive, you also need to consider what would happen if you were to get into an accident. In addition to thinking about the damage you might do to others, consider how the police will view your driving with an immobilised leg. Though there is no law prohibiting you from driving, the accident will most likely be deemed your fault because an immobilised leg hinders your ability to drive. Beyond what the police may be able to charge you with, you will also have to deal with insurance premiums that are likely to go up.
Pain While Driving
A walking cast diverts a lot of the pressure and stress away from the break, however, when driving there are a lot of unexpected things that may come up, even if you are only driving down the street. Jamming on the brakes to avoid a person, an accident, etc., could cause an unbelievable amount of pain or stress on the leg.