We present measurements and electromagnetic simulations of planar Goubau lines (PGL) on quartz substrate up to 1 THz. PGLs are single strip transmission lines. A very high-efficiency planar transition between a standard coplanar waveguide (CPW) and PGL is demonstrated A time-domain electroabsorption sampling method is used to measure the reflected and transmitted waveforms. Transmission of picosecond pulses is demonstrated. We obtain 5 dB of losses around 200 GHz and 12 dB around 500 GHz for a 4.2 mm-long 5 mum-wide strip and two transitions in a back to back topology. The value at 200 GHz is also confirmed with a frequency-domain measurement.