Safety/quietness score functions

It's time to measure more than just travel time! Here's an attempt to summarize a whole bunch of ideas from Slack, many from Michael:

- Measure individual events in the simulation
- When a car wants to over-take a bike
- Biking in the door-zone (next to parking)
- We almost have the ability to modify lane widths now to get this level of detail. I propose manually auditing some cases around Seattle and tagging in OSM.
- Cars turning quickly at the same time that pedestrians are using a crosswalk
- The speed limit of the source/destination road should factor in
- Distinguish cars turning when a light just turns green, vs when the car approaches already going fast
- Correlate everything we do with historic collision data, which we have for Seattle and the UK
- Crosswalks over many lanes
- "The relationship isn't linear (crossing a 8-lane road is typically worse than crossing 4 separate 2-lane roads). You can count the single worst case crossing on each trip, or have some threshold like "4+ lanes" and count how many "bad" ones were crossed. Or just show them all in a histogram."
- Does it matter if there's any vehicles nearby at the time of crossing?
- Other pedestrian safety ideas
- https://www.seattle.gov/Documents/Departments/SDOT/VisionZero/SDOT_Bike%20and%20Ped%20Safety%20Analysis_Ph2_2420(0).pdf
- Intersections with >4 legs are riskier. We may need to do more work on intersection merging to pick up all of these.
- Intersections between arterials and residential streets are more dangerous
- Level of stress, for cyclists
- Many ways to define this...
- http://www.northeastern.edu/peter.furth/research/level-of-traffic-stress/
- https://bna.peopleforbikes.org/#/places/0ea909ec-0b15-4bae-b593-a40da8a72312/
- Eldans' all ages & abilities network
- https://www.seattle.gov/transportation/projects-and-programs/safety-first/vision-zero/resources/bicycle-level-of-traffic-stress
- What percentage of a trip was on a stressful road?
- Do we want to track total miles / time traveled on a stressful road? Or how many trips spent more than 50% of time (or distance?) on a stressful road?

One thing I'm puzzling over is how to use these cost functions. At first we're going to expose new metrics in the UI for individual agents and in aggregate, and as new layers on the map. But we could also use them to change the pathfinding cost functions, making people avoid "dangerous/loud" roads some amount. There's a tension there -- if everybody avoids them too much, we won't measure much "danger." Ideally we could calibrate the routing score function to match what people do in reality, and then take measurements.

There's lots of ideas here; I'll probably start specifically with
1) creating a new static map layer to rank road stressfulness, using one/multiple of the ideas for classification
2) Recording and displaying data for an individual walking/cycling trip. We could show "green/yellow/red" parts of the route, and maybe explain why we classified each segment that way when you mouseover.
3) Figuring out how to summarize this per-trip data in the trip table and the trip summary dashboards, alongside travel time.