Re: Question about traffic flow

The primary cause of the "traffic jam" may be attributed to cautious 
drivers.  These drivers pass the stalled vehicle at a reduced speed in 
hopes of avoiding hitting the stalled car or a person and see for 
themselves the extent of the situation (rubbernecking).  And when one 
driver slows down noticeably, others will follow in hopes to avoid the 
situation as well (an accident, flat tire, stalled car, or even a police 
officer).  This chain reaction then collects in volume as more individuals 
are forced to slow down and maybe even stop due to other drivers slowing 
down, changing lanes, etc.  And once you passed the situation, the road is 
wide open and traffic flow can resume to normal speed.

Now modeling.  At first, I would have said "no, it would be quite difficult 
to simulate uncertainties such as accidents and stalls."  However, I did a 
little homework and found that several universities and traffic institutes 
are working on improving traffic models and computer codes to contain 
"conflicts".  These "conflicts" range from pedestrian traffic to vehicle 
accidents.  Even though the situation you encountered was a "stall" one may 
take the condition to be a "conflict" as well.  I guess no matter how you 
would look at it, at some point in time a vehicle will break down or have 
an accident within a given population and flow stream of vehicles.  This 
would give you a likely probability for encountering a stall or accident 
("conflict") which could then be incorporated within a traffic flow model 
or computer code and be accounted for.

In addition, many traffic codes and models include a mathematical model for 
the "stop and go" wave phenomenon.  I wish I knew more on the subject but I 
have included some web sites I located that have additional information 
about Traffic Models and some specifically that include information about 
model and codes containing "conflicts":
 http://tti.tamu.edu/research/operations/ http://www.unb.ca/web/transpo/mynet/mty80.htm http://www.unb.ca/web/transpo/mynet/mtu3.htm http://rcswww.urz.tu-dresden.de/~helbing/inside.html http://www.hut.fi/Units/Transportation/Research/ http://www.unb.ca/web/transpo/ http://www.swov.nl/en/actueel/swovschrift/Traffic_models,_inner_areas_and_r
oad_danger.html

And these traffic phenomenon are not unique to the United States.  Some of 
the above web sites are from European countries.  And unfortunately, 
accidents, stalls, and other traffic  situations will always occur at some 
point in time inevitably creating a traffic jam.  It's all about mechanical 
unreliability (the breakdown) and human nature (slowing down [a good thing] 
and rubbernecking [a not so good thing]).

Hope this will help answer your questions.