Selecting a line from NextBus data

selectline.sql

SELECT loc_a.oid, loc_a.vehicle, loc_a.route, loc_a.direction, transform(ST_MakeLine(loc_a.the_geom, loc_b.the_geom), 26945) AS the_geom,
	(ST_Length(transform(ST_MakeLine(loc_a.the_geom, loc_b.the_geom), 26945))/
	(EXTRACT(EPOCH FROM loc_b.time) - EXTRACT(EPOCH FROM loc_a.time))) * 
	2.23693629 AS mph, loc_a.time AS starttime, loc_b.time AS endtime
  INTO acrt.lametrolines
  FROM 
    (SELECT *, ROW_NUMBER() OVER (ORDER BY vehicle, time) AS num FROM acrt.nextbus) AS loc_a
    JOIN
    (SELECT *, ROW_NUMBER() OVER (ORDER BY vehicle, time) AS num FROM acrt.nextbus) AS loc_b
      ON (loc_a.vehicle = loc_b.vehicle AND
        loc_a.route = loc_b.route AND
        loc_a.direction = loc_b.direction AND
        (loc_a.num + 1) = loc_b.num)
 WHERE loc_a.time <> loc_b.time;
ALTER TABLE acrt.lametrolines ADD COLUMN traversal int2;
UPDATE acrt.lametrolines SET traversal = EXTRACT(EPOCH FROM endtime - starttime);