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dfsnow / travel-time-matrices

Resources, scripts, and how-tos for calculating national travel time matrices
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Investigate sharp discontinuities near edges of reachable area #2

Closed dfsnow closed 1 year ago

dfsnow commented 3 years ago

Below is a plot of multi-model travel times in Cook County with the following settings:

Starting census tract = 17031031502
Departure time = 2021-04-16 20:21:17 CDT
Maximum walking distance = Infinite
Maximum trip duration = 600 minutes
Maximum number of rides = 5
Transit modes = TRANSIT (any mode) + WALKING
Destinations = All census tracts in Illinois ( + a 100 km buffer) reachable with 600 minutes
Walk speed = 3.6 km/h

cook

The times and structure here look pretty reasonable to me. However, the sharp discontinuities (quick changes from purple/blue to yellow) really shouldn't be possible. I suspect they have something to do with the OSM network in the area, or maybe the walk speed is too low.

eric-mc2 commented 3 years ago

@dfsnow For some perverse reason, the plot look discontinuous or smooth depending on whether I've left or inner-joined the travel times onto the tract geometries, even though the left-over rows from the left-join shouldn't make it into the plot.

But only for IL. Haven't haven't seen discontinuities in DC metro or NY metro areas yet.

A hypothesis from Nico is that these are legit and reflect the edge-of-service at the city border

dfsnow commented 3 years ago

Let's test with DC and see if we see the same thing. I'm going to play around with some of the other parameters this weekend as well. I think the 3.6 km/h walk speed is probably too slow.