Split urban areas crossing multiple states proportional to the population within each state

# :rocket:

- [x] Is your feature request essential for your project?

### Describe the workflow you want to enable
In the current implementation, UA VMT is not split properly when such area lies across state boundaries. The proposed implementation is to split such urban area proportional to the population within each state.

### Describe your proposed implementation, if applicable
A new data source has been found from census data set that gives the population (and land area, etc.) of UA between states.
https://www.census.gov/programs-surveys/geography/technical-documentation/records-layout/2010-urban-lists-record-layout.html
Scroll down one can find a file titled “ua_st_list_all.xls”.