Data source: OpenStreetMap (www.osm.org)
Files processed with OSMOSIS (https://github.com/openstreetmap/osmosis)

1) extract LA region from SouthCalifornia file: 

osmosis --rb file=socal-latest-2019-09-22.osm.pbf  --bounding-box left=-118.66 bottom=33.44 right=-116.95 top=34.33 --wb file=/Users/ihab/Desktop/socal-latest-2019-09-22_extracted-LA.osm.pbf

2) filter LA region osm file (detailed network)

osmosis --rb file=socal-latest-2019-09-22_extracted-LA.osm.pbf --tf accept-ways highway=motorway,motorway_link,trunk,trunk_link,primary,primary_link,secondary_link,secondary,tertiary,motorway_junction,residential,unclassified,living_street --used-node --wb LA-region-2019-09-22_incl-residential-and-living-street.osm.pbf

3) filter south california osm file (coarse network)

osmosis --rb file=socal-latest-2019-09-22.osm.pbf --tf accept-ways highway=motorway,motorway_link,trunk,trunk_link,primary,primary_link,secondary_link,secondary,tertiary,motorway_junction --used-node --wb socal-2019-09-22_incl-tertiary.osm.pbf

4) merge coarse and detailed network

osmosis --rb file=socal-2019-09-22_incl-tertiary.osm.pbf --rb LA-region-2019-09-22_incl-residential-and-living-street.osm.pbf --merge --wx socal-LA-network_2019-09-22.osm