  Urban mobility involves many interacting components: buses, cars, commuters,
pedestrians, trains etc., making it a very complex system to study. Even a bus
system responsible for delivering commuters from their origins to their
destinations in a loop service already exhibits very complicated dynamics.
Here, we investigate the dynamics of a simplified version of such a bus loop
system consisting of two buses serving three bus stops. Specifically, we
consider a configuration of one bus operating as a normal bus which picks up
passengers from bus stops $A$ and $B$, and then delivers them to bus stop $C$,
whilst the second bus acts as an express bus which picks up passengers only
from bus stop $B$ and then delivers them to bus stop $C$. The two buses are
like asymmetric agents coupled to bus stop $B$ as they interact via picking up
passengers from this common bus stop. Intriguingly, this \emph{semi-express}
bus configuration is more efficient and has a lower average waiting time for
buses, compared to a configuration of two normal buses or a configuration of
two express buses. We reckon the efficiency arises from the chaotic dynamics
exhibited in the semi-express system, where the tendency towards anti-bunching
is greater than that towards bunching, in contradistinction to the regular
bunching behavior of two normal buses or the independent periodic behaviour of
two non-interacting express buses.
