I have spent several hours trying to find this for you but have been unsuccessful.
What I CAN tell you is that it is a winning
quadriga in a race in a
circus. If you lighten the
reverse you can see the
palm branches on the horses' heads - especially clear on
the
horse closest to the viewer and also denoted by the longish slanting line between the
head of the furthermost
horse and the driver's
head.
The name in the
exergue is very likely either the name of the driver (aurige) or the name
of the owner of the horses (on images of single horses, the name can be the
name of the
horse).
Searching through
Robert and
Sabatier the closest I could find as far as names
went was the name of the aurige: MATVRVS.
Neither
Robert nor Sabatier list this particular coin of
Trajan, though
Sabatier does list
the
obverse legend for
Trajan with other reverses.
What you need is someone with the new
Trajan catalog (I know
Curtis Clay has one because
he wrote an excellent review of the book and has also himself written articles about
Trajan contorniates. This
contorniate may be in that
work but I don't have it.