Have engines and wheel types affect torque directly, rather than just engines being raw power. This will prevent main battle tanks from hitting 100s mph due to overly big engines, but still be able to effectively crush whatever it presses against, even when accelerating from 0 mph. Unless it’s a zombie hulk, in which case it might take a bit more effort.
Have enemies hit by large, low velocity vehicles take crushing damage rather than impact damage, which scales based on how much weight is distributed where they are impacted. Keep the target stunned and abstractly tucked below the vehicle part if they do and up crushed, only permitting them to smash at the part they’re currently under, or try to wiggle out from beneath the vehicle (unless they’re under a tire, in which case they can only smash).
Now looking back, those additions might not be so simple. I’ll add a simpler one:
Add plastic to the tailoring kit modifications list. Slightly waterproofs the clothing in question, increases warmth, and defenses somewhat. Mildly more bash protective than leather, but slightly more encumbering.
Add plastic bags or the “10 plastic bags” item to the tailoring kit modifications list. Would increase warmth and waterproofing quite a bit, but not as much as wool or fur. A point or two of bash protection, slight encumbrance, but not much else.
Give barbed wire a chance to trip whoever tries to negotiate over it, much like a trap, causing more significant full body lacerations than the previous tiny cuts.
Be able to build a “sheet metal wall” in the construction menu. Needs a tool with hammering, some scrap metal, two pipes, and sheet metal. About as easy to bash through as a glass window, but blocks sight.
Be able to “lean sheet metal on fence”. Essentially makes a fence unchanged, except it now blocks sight. Only requires sheet metal and a tool with hammering, and much less time than a normal sheet metal wall. Bashing can reduce it to a normal wire fence, but the sheet metal makes it slightly tougher than a lone metal fence before.