or:
$doc = array(
    'tags' => [
        'name=A440',
        'highway=secondary',
        'oneway=yes'
    ]
);
$db->poi->ensureIndex( [ 'tags' => 1 ] );

// Road with name=Strand
$db->poi->find( [ 'tags' => 'name=Strand' ] );
// All roads
$db->poi->find( [ 'tags' => new MongoRegex( '/^highway=/' ) ] );
  • One index required
  • Good for finding key/value combinations
  • Good enough for doing the "all roads" question