This function downloads and unzips UK road crash data.
It results in unzipped .csv files that are put
in the temporary directory specified by get_data_directory()
or provided data_dir
.
The file downloaded would be for a specific year (e.g. 2017).
It could also be a file containing data for a range of two (e.g. 2005-2014).
The dl_*
functions can download many MB of data so ensure you
have a sufficient internet access and hard disk space.