Apple has increased the number of drivers for its fleet of autonomous vehicles, with the headcount of testers for its self-driving vehicle systems now at 137 people.Apple has been steadily increasing its group of drivers used to collect data and trial its self-driving car technology on roads in the United States. The company has continued the upward trend by adding more people to the roster.In data from the California Department of Motor Vehicles seen by MacReports, Apple has increased the number of driver permits by 23, bringing the total number of its drivers up to 137. In September, the count was at 114, while in August and May, it was 92 drivers and 76 drivers respectively.Read more