Aspects of the present disclosure relate generally to safe and effective use of autonomous vehicles. More specifically, an autonomous vehicle is able to detect objects in its surroundings which are within the sensor fields. In response to detecting objects, the computer may adjust the autonomous vehicle's speed or change direction. In some examples, however, the sensor fields may be changed or become less reliable based on objects or other features in the vehicle's surroundings. As a result, the vehicle's computer may calculate the size and shape of the area of sensor diminution and a new sensor field based on this area of diminution. In response to identifying the area of sensor diminution or the new sensor field, the vehicle's computer may change the control strategies of the vehicle.