They're just standard Webway Portals (small blast, as pictured above).
You can't stand on them as they're impassable (and round, good luck balancing a model on that). But you can surround them, preventing anything coming through on foot.
As for who can use them, no vehicles at all.
The giant webway you can get for the archon/kabalite/incubi/trueborn Arterial Webway Strike apocalypse formation thingy, on the other hand, specifically allows vehicles.
I dedicate these deaths to Odin Allfather, Spearshaker, One Eye.
Fleet Shadowmaker - Kabal of the Dying Sun; Cult of Marrow Excised; Coven of Lambent Hunger
Sons of the Last Breath - Chaos Space Marines
Host of Shattered Purity - Chaos Daemons