SELECT CASE
    WHEN R.seq = 0 THEN geom
    WHEN ST_DWithin(ST_StartPoint(geom),ST_EndPoint(LAG(R.geom,1) OVER (ORDER BY R.seq)),1) THEN R.geom
    WHEN ST_DWithin(ST_StartPoint(geom),ST_StartPoint(LAG(R.geom,1) OVER (ORDER BY R.seq)),1) AND       ST_DWithin(ST_EndPoint(LAG(R.geom,1) OVER (ORDER BY R.seq)),ST_StartPoint(LAG(geom,2) OVER (ORDER BY R.seq)),1) THEN R.geom
    WHEN ST_DWithin(ST_StartPoint(geom),ST_StartPoint(LAG(R.geom,1) OVER (ORDER BY R.seq)),1) AND ST_DWithin(ST_EndPoint(LAG(R.geom,1) OVER (ORDER BY R.seq)),ST_EndPoint(LAG(geom,2) OVER (ORDER BY R.seq)),1) THEN R.geom
    ELSE R.reverse
    END AS geom,
    R.seq
FROM route R