First Step:

The model is designed to run in 2 by 2 patch size with SCREEN-EDGE-X Size: 
135 and SCREEN-EDGE-Y Size: 149. Due to complications in the program, it is 
not currently saving in this mode. Please set the program to these settings 
before using.

What is it?
This is a model of pedestrian crosswalk traffic. Each red turtle represents 
a pedestrian moving from the right to the left, each white moving left to right. 
Social scientists have observed that human banding is commonly displayed in 
high density crosswalks. In place of random movements, people move in 
coordination with others traveling in the same direction in order to avoid 
oncoming pedestrian traffic.

In order to demonstrate such a phenomenon, this model assumes two general 
laws of travel followed by humans within the crosswalk. 1) When confronted 
head-on by a human moving in the opposite direction, each human will step 
either to the right or left. 2) In order to maximize efficiency, each 
human will follow the travel of an individual in front of them, whether 
he/she is directly or diagonally ahead of them.

How to use it?
This model is meant to model the emergent properties witnessed in a social 
phenomenon.  More specifically, it attempts to re-create, through simple 
rules, what researchers have only been able to observe in real life.  It is 
also meant to be a measure of the different effects of such factors as 
"density" "width" and "columns". 

The DENSITY slider affects the proportion of patches that initially sprout 
a turtle at both screen edges. The higher the density, the more patches 
sprout humans.

The COLUMNS slider defines how many waves of people enter the crosswalk. 
In other words, the slider determines how many columns of turtles approach 
the road from each direction.

The WIDTH slider determines the total area of the crosswalk. The white 
lines illustrate the current width and the borders for where turtles are 
allowed to travel. If a turtle travels outside the crosswalk, it dies.

The CONTINUE switch allows the user to choose the turtle's activities once 
it reaches its destination. Once the turtle makes it across the road, it 
can either stop at the edge of the screen, therefore causing backup across 
the screen, or can continue to the other side of the screen along its 
current pattern. When the continue switch is set to 0, the turtles move 
along in a normal manner. When it is set to 1, the turtles stack up at 
the edge of the screen so as to display the banding lines which they 
formed within the model.

The UNJAM button redirects every turtle momentarily in order to free up 
"traffic jams" within the model.

Extending the model.
The model could be extended in several ways. As it is, the model is subject 
to frequent backups or "jams", which require the Unjam button to clear up. 
While the intent of this is to show the natural patterns of backups, it 
could also be an area for expansion. How could one program each turtle to 
get itself out of a "jam"? What is the most efficient way to unclog backup?

The model currently assumes that people only wish to move left and right 
within the crosswalk. What would happen if turtles were also programmed 
with the intention of travelling diagonally?

Additionally, we can ask questions about other variables: What happens 
if we remove the assumption that each turtle moves at the same speed? Can 
we add a traffic signal?  What if some turtles attempt to break out of the 
bands and form their own paths?  

Can you alter the program so that thicker bands form?

This model highlights the use of the SPROUT function in StarLogoT. In order 
to assign only one turtle to a patch at SETUP, the model uses SPROUT instead 
of CREATE-TURTLES. By doing so, each patch at SCREEN-EDGE-X and SCREEN-EDGE-X 
determine whether or not to create a turtle based upon the user's input 
through the density slider.

Like the model FOLLOWER, this model uses the variable "follow" to latch 
onto another turtle. This variable is set to the other turtle's ID in the 
SEARCH function.

This model derives from a study by Katsuya Yamori at Nara University entitled 
"Going With the Flow: Micro - Macro Dynamics in the Macrobehavioral Patterns 
of Pedestrian Crowds. The article can be found in:

	Psychological Review. 1998. Vol. 105, No. 3, 530-557
	Copyright 1998 by the American Psychological Association, INC.