I didn't attempt to answer - because I just didn't know.
Of course I know what
Peter is referring to, but never knew the name for them.
They were frequently seen on tramcars I believe.
Searching Googoo using various combinations suggests that '
guard rails' or '
lifeguards' is correct (I found a model website that used the term but I can't find it again), though later references of 'guard rail' apply to a rail that prevents opposite wheels from de-railing (current tramcar body designs seem to incorporate solid bodywork where early designs had the rails as discussed above) or a version of Armco barrier rail or similar pedestrian barrier. There are several meanings of 'lifeguard' of course, but it does seem to be used when referring to appropriate Matchbox 'Models of Yesteryear', so I would support
billyboy's 'lifeguard rail'.
Blackpool trams seem to have
lifeguards too . . .
Edited to add:-
http://www.themodelbus.com/kits/rtc.htm