What bicycle safe anti-car road spikes exist?
Keeping cars off a bike path is easily done with bollards. Good solid posts 1-1.5m apart will completely block cars, and the middle one can be a removable, lockable version to allow service vehicle access. Alternatively a gate can be provided next to the bike gap. This also permits horse riders. Where the primary concern is horse riders but bikes are permitted, a gate that a horse can step over is sometimes fitted. A cyclist has to dismount and lift the bike over - one thing on a lightly loaded MTB, another touring with a trailer. Here a picture of one (CC-by-SA David Hawgood via Geograph.org.uk):

In this case it would also be possible to get a bike round the gate.

Some care is needed in designing the layout of bollards and similar to ensure that recumbents and especially trikes can pass, but a straight stretch of path makes this easier. 

I suggest that blocking cars isn't the hard part. Blocking motorbikes is the hard part and not one I've seen a good solution to, as off-road motorbikes aren't much bigger than bikes (narrower than trikes) and can be lifted over a step-over gate.