here is an example of any of text file, stored in primo\content\speedcam folder. in order to get 30mph just replace it w/value of 48km (10*1.609)

X,Y,TYPE,SPEED,DIRTYPE,DIRECTION
-157.7902200,21.3843600,1,30,0,0
-157.7807500,21.3750800,1,30,0,0

or in format of
id,X,Y,TYPE,SPEED,DIRTYPE,DIRECTION

the data from any text file of that folder will automatically included into the binary speedcam.spdb. it is ok to delete it any time to clean it up