Write SQL query to solve given problem: How many of the patients who underwent a 'bone immobilization' procedure have a driver's license?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(DISTINCT T1.patient) FROM patients AS T1 INNER JOIN procedures AS T2 ON T1.patient = T2.PATIENT WHERE T2.DESCRIPTION = 'Bone immobilization' AND T1.drivers IS NOT NULL