Some women in Saudi Arabia are driving cars on Friday as part of a defiant response to the kingdom's traditional ban on women behind the wheel.

Many Saudi women pledged on social media Internet sites to take part in the protest. It may be the largest such mass action since November 1990, when women demonstrators were arrested.

Since demonstrations are banned in Saudi Arabia, women with drivers' licenses obtained in other countries were being encouraged to make individual protests.

Early in the day, some women made trips to the supermarket or just went for drives in Riyadh. Their husbands boasted about trips by posting messages on social media sites.

How widespread the protest might prove to be is open to question. Some women might be scared off by the experience of activist Manal al-Sherif, who was jailed for two weeks after going for a drive and posting video on the internet of the trip.

There is no written rule in Saudi Arabia barring women from driving, only fatwas, or religious edicts, stemming from a strict tradition of Islam called Wahhabism.

Clerics enforcing it claim that if women could legally drive, they would be free to leave home alone and could then interact with male strangers. The prohibition forces families to hire live-in drivers or rely on male relatives to drive.