Easing off the accelerator now will be far easier than slamming the brakes later on.

The project was going ahead smoothly when suddenly orders came from above to bring the whole thing to a halt.

One minute my head and neck are pressed back against the headrest, the next they jerk forward when the driver slams on the brakes.

It's better to have them clamp down now and have a soft landing instead of slamming on the brakes later," Bryson said.

In what has become a too-familiar experience in Tokyo, a crowded subway train screeches to a sudden halt. From around the car, mobile phones start to ring.