* Day of the week: Weekdays see significantly more driving than weekends.
* Time of year: Driving patterns vary seasonally (e.g., less driving in harsh winter conditions).
* Geographic location: Car ownership and usage rates differ dramatically between countries and regions. Highly populated urban areas will have more cars in use than rural areas.
* Definition of "driven": Does this mean a car driven for at least one mile? For more than 30 minutes? The definition significantly impacts the result.
To get an estimate, you'd need to aggregate data from many sources worldwide, which is a monumental task. While precise figures are unavailable, it's safe to say that billions of car trips occur globally each day.
