BURAIDAH, Saudi Arabia—Saudi women's plans to defy their nation's harsh restrictions on them driving is reigniting a fundamental conflict between conservatives and moderates on the kingdom's future.

Even in the country's most conservative town, Buraidah, some traditional women will challenge the de facto ban on driving on Saturday. In the northern desert town where few women are seen in public, let alone behind the wheel, protesters say they have the support of families and friends.

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