Why following the various truck and vehicle terror attacks, have the authorities not done something to stop vehicles mounting sidewalks?

They are.

Modern vehicles are being out-fitted with kill-switches that Police or other central authority can trigger to render any vehicle immobile.

It would make very little difference. They would just use the vehicles in another place. The Muslim demographic is the source of the problem.

We must separate from them. The most efficient way of doing this is by rehomogenising.

Why have the Authorities not done something to stop Muslims mounting other Muslims, this would help prevent a multitude of future terror attacks

No offence intended but this suggestion does have merit.

Such as ? 10 foot concrete barriers ? so how would be cross the road, climb them?