Not a very good one from the footage shown on the BBC. He stopped at the lights going up towards Victoria Street, did a u-turn to get up a bit of speed before crashing into barriers that are designed to stop vehicles ramming into them at the Cromwell Green entrance. So he slowed down, before ramming his car into a place where you have 'relatively' few people (certainly compared to the Westminster Bridge junction and up Whitehall) and a whole bunch of coppers.
Bit of a rubbish terrorist all things considered (and I say this in the sincere hope that anyone that was affected by his actions is not badly hurt)
We're quite fortunate in some sick sense that the guy that did it seems to be a bit thick.
I understand that this is controversial, but I see this as further evidence that current anti-"terror" legislation isn't working.