Traffic experiment doubles travel time

In an effort to address the number of cars on Johannesburg roads, the local authorities have imposed a rule that only cars with 3 or more people in the car may travel in the far right hand lane.  Here are a couple photos taken to demonstrate how well this is working:

It apparently took the photographer 3 hours to travel between Pretoria and Johannesburg instead of his usual 1.5 hours.  I understand how this is supposed to incentivise people to carpool but many people simply don’t work in an office with other people who travel from the same place to the same place at the same time.  This rule seems to be another example of a rule that really wasn’t thought through carefully.  Of course there is always a possibility that the rule is intended to benefit the taxi industry alone?