In fairnesss to the authority who put that barrier in place. They are expecting DF bikes along the path and not trikes and recumbents. If you made the barriers wide enough for trikes then you are opening the gap for motorbikes. Trikes and recumbents are rare by any standard and authorities can be forgiven for not wanting to stump up even more money to design something that may never be used.
If you make the barriers wide enough for most
DF bikes, then many motorbikes can get through too. You cannot distinguish hybrid bikes and motorbikes by barriers and any attempt to do so is doomed to fail, which is why all the current guidance tells authorities not to try. The occasional car-stopping bollard is enough. More annoyingly, often where they still try, it's not fenced in as well as my picture and off-road motorcyclists simply use their fatter tyres and engines to blast through hedges or over scrub! This crime requires policing, not fencing.
And it should be fairly obvious that there are recumbents around here, as King's Lynn had a framebuilder fairly recently (Red Mount IIRC), D-Tek HPVs is just down the road/railway and Mike Burrows is famous and not far away. It's not unusual for me to see people I don't know on recumbents passing through town. I suspect the availability of routes without long/sharp hills makes it attractive for recumbent touring.
Now to cheer me up, have a better bollard:
