segment_duration is not equal to distance/walkSpeed for walk trip legs

[luyuliu]

As title. I guess it's not a r5r problem but a r5's engine problem. Some extreme examples can be rather ridiculous, like this short trip.

from_1000_999.csv

I made the adjustment so that the unit of distance and segment_duration are meters and seconds.

I guess it's because shorter trips will skip some shorter link from the o/d point to the network?

Longer trips' trip legs can also deviate from the walk speed given in the setting. The last-mile leg would usually be slower than the given value, while the first-mile leg would usually be faster than the given value.

from_1094_851.csv

Notice that the short transfer leg too. The speed can also exceed the given walking speed of 1 m/s.

Is this intentional or a bug?

[rafapereirabr]

@luyuliu , thanks for reporting this. I suspect these strange results occur because of where R5 is snapping origin and destination points to the network. So this would be in some ways related to Q1 in our FAQ

You can run find_snap() to determine precisely where R5 is snapping points to. This could give an idea of where the strange results are comming from.

r5r::find_snap(r5r_core, points, mode = "WALK")

[luyuliu]

Thanks. I notice the non-zero results of OD pairs with same O and D. I also guess the same for the first-mile leg, but the last-mile leg is always faster than the set speed, which I don't know why. I think snapping can only increase the total length but not decrease it?

[rafapereirabr]

R5 considers that the person would walk in Euclidean distance from the input point to the snapped location. This sould be the same when travelling between the destination point and its respective snapped location.

In both segments, we would expect the person would travel using the speed set by the user. If there is a simple reproducible example where the speed is different than the set speed, this could possibly be a bug upstream in R5.