The 26-year-old royal is travelling to Barocca d'Alva with her horse Toytown and groom Kelly Davies to compete in an international equestrian meeting but has insisted on doing most of the driving for the long journey.
A source told Britain's Daily Mail newspaper: 'Zara said she thought it would be fun to drive down to Portugal, so she has volunteered to be behind the wheel most of the way.
'It's not that unusual for her - she doesn't ask for special treatment because she is royalty. She is always happy to get stuck in like everyone else.' Zara, who is the reigning world three-day eventing champion, explained Toytown can't wait to get to Portugal for the competition, which is being held on February 27-March 2 and March 5-9.
She said: 'He gets bored if he stays out too long, so he's been schooling and galloping and is in really good form.' The royal, who is dating England rugby player Mike Tindall, is part of the British Olympic equestrian team and hopes to pick up a medal at the Hong Kong games in August.