SELECT ST_AsGeoJSON(ST_Transform(way, 4326)) AS geometry
  FROM pgr_dijkstra(
'SELECT osm_id AS id, source, target, st_length(way) as cost FROM planet_osm_roads',
34, 3000, false
  ) as di
  JOIN planet_osm_roads pt
  ON di.edge = pt.osm_id ;

SELECT ST_AsGeoJSON(ST_Transform(way, 4326)) AS geometry
  FROM pgr_dijkstra(
'SELECT osm_id AS id, source, target, st_length(way) as cost FROM planet_osm_roads',
'SELECT pl.source::integer FROM planet_osm_roads pl WHERE pl.name LIKE ''street_name'' LIMIT 1',
 3000, false
  ) as di
  JOIN planet_osm_roads pt
  ON di.edge = pt.osm_id ;