How old are the ties? I think the stuff leaches out over a long period of
time....
Creosote is a by product of the turpentine industry, pine tar creosote;
apparently has medicinal uses: used to see cans of it in the drug store.
Coal tar creosote is different, is carcinogenic and probably has herbicidal
qualities.
Still creosote and creosote-treated RR Xties are nowhere near as dangerous as
CCA pressure treated lumber.
I was once a landscape contractor and built many patios, steps and planters,
often with green RR Xties from the sawmill
and painted them with creosote. Kinda strong smelling stuff :-) It was the termite treatment of choice for house and building underpinnings
for many years.
Its a lot safer than CCA lumber.
If BK's ties are old and not smelly they are probably safe for raised bed
construction, though I would paint the inside surfaces
or line them with some other wood, plastic, etc.