Estimate travel time to a test center.
Journey time is distance divided by average speed, but for a test the buffer matters more than the base figure. A thirty percent traffic allowance covers ordinary congestion, and parking plus finding the room routinely takes fifteen minutes at an unfamiliar venue. Adding a deliberate arrival margin on top produces the departure time, because arriving late to an examination is usually not recoverable.
Journey time
Driving minutes = distance km x 60 / average speed km/h; buffered = driving x (1 + traffic buffer)
Departure allowance
Leave early by = buffered driving + parking and walking + arrival margin
Twenty-five to forty kilometres an hour door to door is realistic in urban traffic, well below the speed limit. Using the limit as an average is the commonest cause of underestimating.
Thirty percent covers routine variation. For a high-stakes examination, a fixed extra half hour on top is cheap insurance against a road closure or a missed turn.