Answer:
Temporary road closure or coffee break
Step-by-step explanation:
Assume a car started on a trip at 08:00 and the graph below shows the total distance it travelled every half-hour.
We see that after 1 h (at 09:00) the car was a certain distance from the start.
A half-hour later (at 09:30) the car was still at the same distance.
The car was stopped.
There may have been a bad traffic accident that closed the road or the driver may have stopped for a quick cup of coffee.