Olympics 2012 track cycling

Exactly. The rules simply use the term 'draw away' this doesn't say in which direction.
Simply put though, the lead rider needs to be out of the way of the other before that last 15m point. Not sure the dynamics of the race /track geometry would actually allow the lead rider to still be ahead if they'd swung right up...unless he/she was still hammering it and rider 2 was suddenly a bit slow

The full text of Art 3.2.153 is:
3.2.153 A team shall be relegated to the last place in the stage of the competition if one of the following infringements has been committed:
1) if a rider draws away by more than 15 metres before the end of the lap that he is to lead
2) if a rider does not draw away by more than 15 metres after the end of the lap that he was supposed to lead
3) if one rider pushes another.

The wording is so poor you could argue the 15m must be measured between the riders... though that would be insane.

If the first rider had completely dropped the second, could 'draw away' allow both to complete the race inside the sprinter's line? (with the time taken on the second rider of course.) i.e. draw away ahead? What about if the first rider dropped the second then pulled out of the path of the second at some point before going 15m beyond the end of their lap? i.e.draw away to the side? Both of these seem possible to me, but the first impractically vague as a rider's influence fades slowly behind them.

In loose language, what's wanted is that each rider must constrain their team's performance until their lap is completed, and must cease contributing after their lap. I think that 'draw away' is a fine term to describe ceasing to contribute, but a poor way of describing their constraining effect during their lap.

The rules could make the rider a constraint on their team by requiring they be ahead until their lap is completed, and require that they cease contributing by drawing away to the side after their lap. Lead could simply be measured from the front of front wheels (allowing overlap). No transition zone is necessary: the first rider could draw away to the side (or ahead) before the line but remain in the lead until after the line.

But it seems reasonable to allow some kind of transition buffer where constraint is released but contribution still allowed to make compliance easier. 30m is less than 2s at race speeds.

Constraining the following rider to not overlap the first rider would be a plausible alternative but seems un-necessarily restrictive. I don't see that overlap is a significant advantage: the following rider would have to cover the distance sooner or later and is giving up the shelter of the lead rider to do it early. The freedom might let a team slightly adjust how the work is shared, but so does the transition zone.