This function classifies speeds in miles per hour (mph) into categories.
Examples
classify_speeds(c(15, 25, 35, 45, 55, 65))
#> [1] "<20 mph" "20 mph" "30 mph" "40 mph" "50 mph" "60+ mph"
# Returns: "<20 mph", "20 mph", "30 mph", "40 mph", "50 mph", "60+ mph"