A classic example is the "Tamale turn", pictured at left. In Tamale, if you are making a left turn off of an arterial, and there is vehicle waiting to turn left ON to the arterial, rather than pass in front of the other vehicle, you pass behind them, while they simultaneously turn onto the arterial.
One can see why drivers might think this makes sense. Both vehicles can turn at once, and if the arterial is busy, the vehicle waiting to turn on to it can take advantage of the other vehicle slowing down.
But as traffic gets denser, the Tamale turn becomes more hazardous. If there are several vehicles waiting to turn on to the arterial, the vehicle turning off the arterial has to negotiate a route behind the turning vehicle, and in front of the waiting vehicles, who may not be on the lookout for a turning vehicle. And more vehicles in the intersection at once raises the risk of a collision as well.
As Tamale's traffic worsens, many similar traffic norms, such as running red lights and passing on the right, technically illegal but general practice in Tamale, will become less efficient and more hazardous. But they will already be ingrained as the standard.
What to do? Some ideas:
1. Give driver's licenses based on merit rather than bribes, to give drivers an incentive to learn the rules on the books.
2. Ticket drivers for practices that threaten public safety rather than focusing on trivial offenses easy to convert to payouts.
Your additional ideas are welcome in the comments!