The problem is you'll only get into the while if @comment_row is true, so testing if (@comment_row) inside the while is useless.

$comment_sth->execute($id)
or die "Couldn't execute comment query: ".$DBI::errstr;

my @comment_row;
my $comment_count;
while (@comment_row = $comment_sth->fetchrow_array) {
   my ($speedtrap_id,$comment_id,$comment_text,$comment_date,$commente
+r) = @comment_row;        

   $comment_count++;

   print <<EOF;
<tr> 
<td colspan="2" bgcolor="#E6ECF0">$comment_text</td>
</tr>
EOF
}

print <<EOF unless ($comment_count);
<tr>                            
<td colspan="2" bgcolor="#E6ECF0">There are no comments from others fo
+r this speedtrap.</td>
</tr>
EOF
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