Calculating different times for up- and downhill walking

Question

Hello everybody,

I'm working on a project, where I'm calculatig the service area of public transport stops. As cost argument I use the walking time, which I calculate from the path length and a fixed walking speed.

Now, I'd like to expand the model by making the walking speed dependent from the slope the path has, so that upwards directed paths generate a lower speed than downward directed. To generate my network dataset, I use the Swiss topographic landscape model swissTLM3D (https://www.swisstopo.admin.ch/en/geodata/landscape/tlm3d.html), which delivers a route network in the form of PolylineZ lines and so has an elevation information within the geometry.

I'm at the moment stuck by how to integrate the elevation information into the time formula. Does anyone have some advice on handling this?

Thanks for your help!

Stefan

JaySandhu · Answer

You can add two fields, FT_WalkingMinutes and TF_WalkingMinutes and compute the travel time for each road based on up hill and down hill slope for that street segment. You can use Tobler's hiking formula to compute these values based on the slope. For more information, see:

Tobler's hiking function - Wikipedia

Jay Sandhu

jcarlson · Answer

Have you checked this page out yet?

There should be a topology rule to check that your network segment Z values are always increasing or decreasing along a given edge, so first check to see that your edges all follow this rule.

It's been a while since I have worked with NA, so I don't know if this can be calculated within the travel modes, or if it needs to be calculated to its own field. In any case, with segments that only increase/descrease in elevation, you can take the min/max Z values of each segment to calculate a slope for the segment. Positive for upward slopes, negative for downward, in the direction of the edge.

With that value, it's simply a matter of looking at the calculated slope and applying the appropriate increase/reduction in speed based on the slope value and whether the traveler is moving with or against the edge direction. I'd use a simple function evaluator to multiply the "flat walk time" by a coefficient, but what the coefficient values you pick are up to you.