In a traffic jam, no vehicle can go at the same time. So, if one car is going slow and another car is going too fast, the other car will not be able to overtake it. This situation does not happen with a computer or a software program. It works because a computer or software program has an algorithm which determines the speed of each vehicle based on its own speed and position in relation to other vehicles.
In this particular situation, there are two cars that have been assigned different speeds according to their assigned positions. The first car has been assigned a low speed and the second one has been assigned a high speed. In this case, the first vehicle cannot go faster than the second one while both vehicles are speeding up towards each other creating traffic jams on roadways.