Others already told you how you could change the data structures. If you are still curious how to get the original hash, try this:

my $skip_first;
my %Belfast_car_dealer_hash =  map { $skip_first++ ? ($_ => 1) : () } 
                               @{ $car_city_dealer_aoa[0] };
print Dumper \%Belfast_car_dealer_hash;
[download]

I also noticed the script is missing warnings turned on.