According to the Center for Universal Design, headquartered in North Carolina State University, UD has seven basic principles.
7. Size and Space for Approach and Use
The size and space should not be constraint. Ease of access should be the desired goal targeting space provided for approach, reach, controls and manipulation regardless of the body size, posture or mobility of user. In this picture subway gates is easily accessible by a person in a wheelchair or with a person carrying huge baggage or even with an obese commuter.