Left') != -1) {
    this.steering += (this.steering < this.maxsteering) ? this.steeringdelta : 0;
  } else {
    this.steering *= this.straightendelta;
  }
  
  // acceleration
  if (this.engine.keysdown.indexOf('ArrowUp') != -1) {
    this.speed += (this.speed < this.maxspeed) ? this.acceleration: 0;
  } else if (this.engine.keysdown.indexOf('ArrowDown') != -1) { // reverse
    this.speed -= (this.speed > -this.maxspeed / 2) ? this.acceleration : 0;
  } else {
    this.speed *= this.deceleration;
  }
}
   