Simple Evacuation Model in Netlogo

After talking with some colleagues about the problem I decided to construct a simple model that simulates how people in a city who are told to evacuate might make the decision to leave or stay. It is documented that many people either choose not to evacuate after being warned while many others simply can't because they lack the means (transportation, social network outside of their neighborhood, etc.).

The model is straight forward - a user specified number of agents are chosen to receive the evacuation notice. Every cell is randomly assigned a decision value that represents the likelihood that they'll actually leave. If that value is above some threshold, then the cell decides to evacuate (represented by green), otherwise they'll stay (red). The blue cells haven't heard one way or the other about the evacuation.

Next all the cells look at their neighbors and see if they've received the evacuation notice - if they haven't nothing changes. If their neighbors have made a decision it will affect the previous mentioned decision value either positively (if their neighbor is evacuating) or negatively (if their neighbor is staying put).

What we see is that there are random cells throughout the region that decide to stay - and also larger clusters (neighborhoods).

It is a very simple model - but I think it captures some of the dynamics of this process. Here is a link to the model: http://www.acsu.buffalo.edu/~mjwidene/evacmodel.nlogo (NOTE: Right click and save as - otherwise you'll get text. Also you need Netlogo to run the program).

And for those interested here is the code:

patches-own [aware? prob-evac evacuate? influence no!]

to setup
  ca
  ask patches[
    set aware? 0
    set pcolor blue
    set prob-evac random-normal .5 .3]
  repeat num-initial[
    ask one-of patches[
      set aware? 1
      set pcolor orange]]
  setup-initial-decision
end

to setup-initial-decision
  ask patches with [aware? = 1] [
    ifelse (prob-evac > .5)
      [set evacuate? 1
       set pcolor green]
      [set evacuate? 0
       set pcolor red]
      ]
end

to go
  display
  ask patches[
  if (prob-evac < .1)
    [set no! 1
     set pcolor red]
  look-at-neighbors
  make-decision
  ]
end

to look-at-neighbors
  set influence (count neighbors with [evacuate? = 1])
  if (no! = 0)[
  set prob-evac (prob-evac + .3 * (influence / 8))]
 


end

to make-decision
  ifelse (count neighbors with [evacuate? = 1] != 0)
    [ifelse (prob-evac > .5)
      [set evacuate? 1
       set pcolor green]
      [set evacuate? 0
       set pcolor red]]
    [if (prob-evac > 0.1)
      [set prob-evac (prob-evac - .1)]]

end

The Chicago "L" system

Whether we call it the "L" the "El" or just "the train," the rail-based transit system in Chicago is definitely one that we locals love and love to hate. Much like most other transit systems in Chicago, the El was designed in a manner to help provide rapid transit to the CBD of Chicago, better known as the Loop. The interstate highway system and the commuter rail system (Metra) are designed in a similar manner.

The L in Chicago remains a very affordable method of transversing many miles of urban Chicago, but the system is really only fast, functional and interconnected if your travel plans lead you to the Loop area. For a traveler who might live in Uptown (perhaps near the Wilson stop on the Red line) and work in Cicero (near the 54th/Cermak stop on the Pink line), travel times are extensive, connections to local buses are infrequent, and the L system becomes a burdensome method of travel.

There are often discussions of expansion of the fixed rail system in Chicago, but little has been done with local, state or federal funding to do much with these ideas. Plans become burdened by battles between wealthier suburban interest groups who prefer money be spent on commuter train expansion (Metra) and poorer, often minority, urban interest groups who would like to see El expansion, outer loop rail construction (connecting the spokes of the current CTA "L" system) and improvement of existing facilities

The battle has implications both for transportation options and for economic development opportunities. There are a plethora of sources that point to the benefits of Transit Oriented Development (TOD) and the benefits for the immediate communities or commercial districts. While the battle for funds begins with appropriations for engineering, planning and construction, the war continues with the longer term implications of economic benefits associated with rapid transit.

Plans for the expansion of the CTA "L" system can be found on the CTA website. Details for the expansion of the CTA Red line from 95th St to 130th St, the expansion of the Orange line from Midway Airport to Ford City Mall, the expansion of the Yellow line deeper into suburban Skokie and the elusive "Circle Line" are detailed on the site (more discussion of this plan will follow).

Subways

Or, Five. Five dollar. Five dollar sub-fare.

Over the past few weeks I made my way to Boston and Washington, D.C. and got to utilize their respective rail systems (the T and Metro) a good amount. I have to say that I found riding the T to be a much better experience (despite it being an older system) thanks mostly to the bustling and vibrant atmosphere underground. Where the T had vendors and art, the Metro had dark brown signs reminding you not to drink or eat and brutalist architecture.

Maybe this has to do with the system being located in the nation's capital (no tomfoolery allowed), but it all seemed a little excessive. Being underground in the D.C. stations left me thinking that adding a human touch could go a long way.

Then again, it got me where I needed to go relatively quickly and for only a few bucks.

Here is a site passed on to me by a friend that has some wonderful images from subway stations around the world. Maybe one day D.C. will renovate their system to make the underground experience a little less depressing!

http://www.designboom.com/weblog/cat/9/view/8346/subway-architecture.html

Look for future blogs on the impact increased ridership might have on current subway infrastructure and on the question of 'how hard is it to add new lines to current systems?' For the latter post, I'll look at how subway construction in Buffalo, NY killed a once vibrant part of the downtown.

I know my experiences on these systems (and most other large city subways) are limited - so if you know them better I'd be interested to hear your impressions.

Short intermission

Updates are coming soon! I'm presently in Boston - and will be back in Buffalo this weekend.