At moderate traffic volumes, a single car moving at randomly fluctuating speeds can cause traffic jams in its wake.
You’re confined to a single lane as you drive along a narrow, winding road. The car in front of you suddenly slows, then just as inexplicably accelerates a short time later, only to slow again. As you keep adjusting to the leading car’s erratic speed changes, you sometimes find a clump of vehicles closely tailing you and, at other times, only a few vehicles in sight.
Computer simulations now suggest that at moderate traffic volumes when vehicle flow should be relatively stable, a single car moving at randomly fluctuating speeds within a steady stream of traffic can by itself create waves of congestion that propagate down the road behind it. Cars far from the offending vehicle can find themselves unexpectedly caught up in localized traffic jams that have no apparent cause. Takashi Nagatani of Shizuoka University in Hamamatsu, Japan, reports the findings in the April Physical Review E.
The amount and type of congestion induced by an erratic driver depend on how much the leading car’s velocity fluctuates, even when its average speed matches that of the rest of the traffic, Nagatani reports. Indeed, an individual driving erratically enough can readily induce the sorts of traffic jams normally associated with much heavier traffic (SN: 7/3/99, p. 8: http://www.sciencenews.org/sn_arc99/7_3_99/bob1.htm).