The 1935 Division of Highways Map of Los Angeles reveals more detailed information about the gap on LRN 172. The western half is shown to end at San Gabriel Boulevard (then California State Route 19/LRN 168) via 3rd Street, Pomona Boulevard, Mesa Drive (now Potrero Grande Drive) and Hill Drive.
The eastern half of LRN 172 is shown to resume east of Anaheim Puente Road (now Azusa Avenue) along 5th Avenue (now Colima Road). LRN 172 is shown following what is now Golden Springs Drive and Brea Canyon Road to LRN 19 near Walnut Station.
The 1936-37 Division of Highways Map displays California State Route 19/LRN 168 realigned onto Rosemead Boulevard north of Montebello. The western half of LRN 172 is shown extended over the Rio Hondo Bridge via San Gabriel Boulevard.
The March/April 1965 California Highways & Public Works announced construction on the Pomona Freeway was either under construction or contracted via six project zones between East Los Angeles to Jellick Avenue. The East Los Angeles Interchange-3rd Street segment of the Pomona Freeway is noted to have an anticipated completion during Fall 1965.