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I want to estimate a spatial logistic regression model for car crashes in Milan using R. I downloaded data from OSM for several highways segments in Milan using the R package osmdata. The response variable of my model is a binary variable which is equal to 1 if at least one car crash happened less than approximately 10m from a street segment, otherwise is 0. I'd like to add to the covariates of the model a new variable that expresses the shortest-path distance between the middle-point of each segment and the nearest roundabout/school/hospital. The shortest-path distance should be estimated on a street network.

This is a small example to show what I mean.

# packages
library(dplyr)
library(sf)
library(osmdata)
library(stplanr)

Download highways data from OSM. This is just a small part of the complete dataset of all highways, which means that the resulting street network is not connected. I can also provide the code to create the complete dataset of all connected highways if it's important to answer my question.

# highways data
milan_highways <- opq("Milan, Italy") %>% 
  add_osm_feature(key = "highway", value = "primary") %>% 
  osmdata_sf() %>% 
  trim_osmdata(bb_poly = getbb("Milan, Italy", format_out = "sf_polygon")) %>% 
  magrittr::use_series(osm_lines) %>% 
  st_transform(crs = 32632) %>% 
  select(osm_id, name, highway)

Download data for all roundabout and estimate the coordinate of the centroid of each polygon.

# roundabout data
milan_roundabouts_lines <- opq("Milan, Italy") %>% 
  add_osm_feature(key = "junction", value = "roundabout") %>% 
  osmdata_sf() %>% 
  osm_poly2line() %>% 
  magrittr::use_series(osm_lines) %>% 
  st_transform(crs = 32632)

my_roundabouts_centroids <- milan_roundabouts_lines %>% 
  st_cast("MULTIPOINT") %>% 
  mutate(at_least_five_points = purrr::map_int(geometry, length) >= 5L) %>% 
  filter(at_least_five_points) %>% 
  st_cast("POLYGON") %>% 
  st_centroid()
#> Warning in st_centroid.sf(.): st_centroid assumes attributes are constant
#> over geometries of x

Now I use the function SpatialLinesNetwork of the stplanr package to estimate the street network.

# highways network 
milan_highways_network <- SpatialLinesNetwork(milan_highways)

Now I'm not sure on how to proceed. My idea is to use the function find_network_nodes to determine the closest node to each segment and each roundabout and the function sum_network_links to estimate the network shortest-path distance between every combination of nodes and take the minimum. The problem is that I'm not sure how to code this idea and if it's good or not.

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