== Highway Model Design ==

First draft of data structure for representing a highway network that can model traffic congestion.

[[Image(intersection_sketch.jpg)]]


'''Highway''' (as shown in sketch) is a highway name and a list of LDS's (Lane Detector Stations).

'''Intersection''' is a postmile number and a cross street identifier.

'''Junction Map''' is a data structure to model highway intersections (junctions), 
A map that associates highways to the cross streets that intersect them.


'''Example Map'''

Hwy 123: [(17, Hwy 456), (54, Hwy 789)][[BR]]

Hwy 456: [(93, Hwy 123), (117, Hwy 10A)][[BR]]

Hwy 789: [(22, Hwy 123)][[BR]]


In the example Hwy 123 has two cross streets: Hwy 456 at postmile 17 and later at postmile 54 it crosses Hwy 789.


== Simulating Congestion ==

Alternative 1.  Every 30 seconds traverse the network from the incident origin point to find the next LDS that is unaffected, then change its state.
Pro: Simple concept, needs only the data structures above.
Con: In a very large network performance would be slow.

Alternative 2.  Maintain a "state" that knows the current extent of congestion and can quickly identify next LDS to be changed.
Pro: Better performance.
Con: Additional data structures needed.

Decision: We prefer alternative 1.  We don't expect out network to be large enough for performance to be a factor.  Even a list of thousands of LDS could be traversed in a second and we have 30 second intervals between ATMS updates.