2020-05-08 02:13:18 +03:00
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# How A/B Street works
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2020-05-08 03:22:35 +03:00
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The big caveat: I'm a software engineer with no background in civil engineering.
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A/B Street absolutely shouldn't replace other planning or analysis. It's just
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meant to be an additional tool to quickly prototype ideas without expensive
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software and formal training.
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2020-05-08 02:13:18 +03:00
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2020-05-08 03:22:35 +03:00
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This page gives a non-technical overview. See
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[here](https://github.com/dabreegster/abstreet/#documentation-for-developers)
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for details.
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2020-05-08 02:13:18 +03:00
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2020-05-08 03:22:35 +03:00
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## The map of Seattle
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The map in A/B Street is built from
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[OpenStreetMap](https://www.openstreetmap.org/about). You will notice many
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places where the number of lanes is wrong; let me know about these, and we can
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contribute the fix to OpenStreetMap. Many sidewalks and crosswalks are also
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incorrectly placed.
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People in A/B Street have to park their cars somewhere. I can't find good data
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about either public or private parking. For now, I'm using a Seattle
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[GeoData blockface dataset](http://data-seattlecitygis.opendata.arcgis.com/datasets/blockface)
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to guess on-street parking, but this is frequently wrong. I'm assigning every
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building one offstreet spot. This is wildly unrealistic, but I have nothing
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better yet.
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There's also no public data about how traffic signals in Seattle are timed. I'm
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making automatic guesses, and attempting to manually survey as many signals
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in-person as I can. I could really use help here!
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## The traffic
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Vehicles in A/B Street instantly accelerate and brake. They change lanes only at
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intersections, and they can't over-take slower vehicles in the middle of a lane.
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People walking on sidewalks can "ghost" through one another, or walk together in
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a crowd -- before COVID-19, this was a reasonable model in most areas. Despite
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these limits, I hope you'll find the large-scale traffic patterns that emerge
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from the simulation to be at least a little familiar from your real-world
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experiences.
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People in A/B Street follow a specific schedule, taking trips between buildings
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throughout the day. The trips come from
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[PSRC's Soundcast model](https://www.psrc.org/activity-based-travel-model-soundcast),
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which uses census, land-use, and vehicle count data to generate a "synthetic
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population" roughly matching reality. The trip data is from 2014, which is quite
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old.
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When you make changes to the map in A/B Street, exactly the people still take
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exactly the same trips, making the same decision whether to drive, walk, bike,
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or take transit. Currently, your changes only influence their route and
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experience along it.
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## Missing things
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Light rail, shared biking/walking trails like the Burke Gilman, and ridesharing
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are some of the notable things missing right now.
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