How to model a database to retain driver related information?
Assuming there is a 'company' table as well that drivers can be associated to?

If so, one option is as follows:

Driver:


Driver_ID (PK)
Vehicle_ID (FK to Vehicle... nullable)
Company_ID (FK to Company... nullable)
solo_driver (boolean value [kind of optional, but could be useful])
other Attributes...


Vehicle:


Vehicle_ID (PK)
Company_ID (FK to Company... nullable)
Other Attributes...


Company:


Company_ID (PK)
Other Attributes...


If the driver is a solo-driver, then they have an associated Vehicle_ID
If the driver is a company-driver, then they have an associated Company_ID
- The company_ID would have associated (one-to-many) vehicle_ID's