If you need to know how to arrive from Barcelona city or airport to the UAB Campus check this UAB document written in Catalan but with maps [1] which are useful for everybody.
There is a timetable [2] of trains available at the Ferrocarrils de la Generalitat [3] website in Catalan, Spanish and English.
This is the procedure to reach IIIA from the Universitat Autònoma Train Station of Ferrocarrils de la Generalitat:
Some train schedule information is available on the RENFE website [4] in Spanish. The station train frequency is about half an hour from 7:30 AM to 8:00 PM.
This is the procedure to reach IIIA from the Bellaterra-UAB Train Station of RENFE.
For those uneasy with procedural knowledge, there is a declarative representation of the route (i.e., a map) below.
Links:
[1] http://www.uab.es/servlet/Satellite/Planols/Accesos-al-campus-de-la-UAB-1096476550065.html
[2] http://www.fgc.net/accesible/eng/viatjar/bcn_valles.htm
[3] http://www.fgc.net/accesible/home.asp
[4] http://www.renfe.es/cercanias/barcelona/index.html
[5] http://maps.google.es/maps/ms?ie=UTF8&hl=es&msa=0&msid=115762204632272229407.000001127ad4d653fcdde&ll=41.503355,2.109568&spn=0.011876,0.019269&iwloc=000001127adaaf9af15ad&source=embed