We present the results of \psrpi , a large astrometric project targeting radio pulsars using the Very Long Baseline Array ( VLBA ) .
From our astrometric database of 60 pulsars , we have obtained parallax-based distance measurements for all but 3 , with a parallax precision that is typically \sim 45 \mu \mathrm { as } and approaches 10 \mu \mathrm { as } in the best cases .
Our full sample doubles the number of radio pulsars with a reliable ( \gtrsim 5 \sigma ) model-independent distance constraint .
Importantly , many of the newly measured pulsars are well outside the solar neighborhood , and so \psrpi brings a near-tenfold increase in the number of pulsars with a reliable model-independent distance at d > 2 kpc .
Our results show that both widely-used Galactic electron density distribution models contain significant shortcomings , particularly at high Galactic latitudes .
When comparing our results to pulsar timing , two of the four millisecond pulsars in our sample exhibit significant discrepancies in their proper motion estimates .
With additional VLBI observations that extend our sample and improve the absolute positional accuracy of our reference sources , we will be able to additionally compare pulsar absolute reference positions between VLBI and timing , which will provide a much more sensitive test of the correctness of the solar system ephemerides used for pulsar timing .
Finally , we use our large sample to estimate the typical accuracy attainable for differential VLBA astrometry of pulsars , showing that for sufficiently bright targets observed 8 times over 18 months , a parallax uncertainty of 4 \mu \mathrm { as } per arcminute of separation between the pulsar and calibrator can be expected .