#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

# Assuming these are [ in, out ]
my @travel_times = (
    [  1,  5 ],
    [  2,  5 ],
    [ 20, 15 ],
);

my %count;
foreach my $time (@travel_times) {
    $count{in }{ $time->[0] }++;
    $count{out}{ $time->[1] }++;
}

print Dumper \%count;

##</code><code>##

$VAR1 = {
          'out' => {
                     '15' => 1,
                     '5' => 2
                   },
          'in' => {
                    '1' => 1,
                    '2' => 1,
                    '20' => 1
                  }
        };