Have you noticed at various intersections there is a crosswalk, but there is also a road surface line painted before the crosswalk? Have you ever wondered why there was a need for the extra line when there is already a crosswalk?
The purpose of the road surface line before a crosswalk is your indication of where you need to stop your vehicle. For safety reasons you are supposed to stop your car before the first surface line and that line should still be partially visible from your vantage point when stopped. Why, you might ask? The purpose behind this is keep the crosswalk clear so that pedestrians may cross without having to walk around a vehicle or have a vehicle block the pedestrian from the view of other drivers, which could lead to injury or death.
An additional reason for these road surface lines is to allow enough room for other vehicles which are turning to be able to make the turn without the threat of hitting your vehicle.