There is one station that I disregarded in my Severn Beach Line usage figures analysis (see link below.)
http://www.savethetrain.org.uk/forum/index.php?topic=577.msg1746#msg1746

St Andrews Road is the intermediate station between Avonmouth - Severn Beach. Its weekday service is provided more by replacement bus than by train , and the bus observes ALL stops between Avonmouth - Severn Beach.

This , in my view , makes it impossible to come to an accurate St Andrews Road usage figure. Estimates have ranged from 4 (Jacobs) to as high as 15 passengers per day.

Judging by source information , the true figure (if you can arrive at a strictly "true" figure) is somewhat higher than 15 , especially if you take into account the number of passengers who regularly board "en - route" , for example , the 0816 & 1645 buses from Severn Beach.

Here is a link that gives a good description of what its like to travel on this unique railway line , which has been recommended by Thomas Cook's European Railway Guide as one of the scenic routes of Europe.
http://www.david.frih.net/severn/

For me , the most interesting (if perhaps not the most scenic) part of the journey is clattering over the tracks approaching St Andrews Road station.

On the one side , you have the line to Avonmouth , which the Jacobs Greater Western Franchise Replacement Outline Business Case Report recommended truncating at Clifton Down.

On the other , you have the line to Filton , which Jacobs rejected introducing a passenger service on in its draft report and on which up to 20 extra freight trains per day are planned , and also the line to Severn Beach , on which the same report RECOMMENDED re-introducing the through train services that have been replaced by bus.

In the middle , you have St Andrews Road station & Avonmouth Docks (link below.)
http://www.bristol-rail.co.uk/standrewsroad.php

Not far away , you have Cabot Park (link below.)
http://www.cabotpark.co.uk/pages/whychoose_cabot.asp

Here is a further link on the Severn Beach Line.
http://www.johnrogers.pwp.blueyonder.co.uk/fosbr.htm

Since the above link was written , the Bristol City Council subsidy has been withdrawn.