In most areas, ONE vehicle is allowed to pull up over the crosswalk line with the front end of their vehicle, wheels straight, and wait until your path is clear (oncoming vehicles and other crosswalk/.road users approaching).
If an oncoming vehicle is making a left turn at the same time you are, you may proceed if your path is clear, because the oncoming, left-turning vehicle wont block your path. That vehicle is also making a left turn.
You may also complete your turn when your light turns yellow as long as your path is clear. This is why one vehicle may wait in the intersection when making a left turn at a solid green light. by allowing one vehicle to enter the intersection on a solid green light, awaiting a clear path or yellow light, keeps traffic moving. At least ONE vehicle will turn per light during times of heavy traffic.
You may also want to inquire about this at your local DMV office. Talk to an Examiner or leave them a note with your phone number.
I hope this information is helpful to you.