It seems ED capacity and overcrowding issues are a near-universal phenomenon.  This paper, published in Accident and Emergency Nursing, describes the situation at  Christchurch Hospital, New Zealand.  This tertiary level facility with an emergency department sees on average 65,000 patients per year. There are no other EDs to whom patients can be diverted, and so despite admission rates from the ED of up to 48%, they cannot go on divert.

The problem has reached crisis level in a number of countries, with significant implications for patient safety, quality of care, staff ‘burnout’ and patient and staff satisfaction. There is no single, clear definition of the cause of overcrowding, nor a simple means of addressing the problem. For some hospitals, the option of ambulance diversion has become a necessity, as overcrowded waiting rooms and ‘bed-block’ force emergency staff to turn patients away.

It seems that most of the factors impacting ED overcrowding in New Zealand are no easier to resolve then they are here.

The focus in more recent times has shifted to view the problem from a wider perspective. Issues such as ‘bed-block’ have been identified (where patients cannot be moved from the ED facility to definitive treatment areas) indicating the inability of hospitals to respond to supply and demand surges, together with the need for ambulance diversion and related health system inefficiencies acknowledged as significant contributing factors. ...While it is often necessary to deal with single aspects at a time, due to the sheer size of the problem, this must be done within a framework that acknowledges that other factors impact on the likely outcome.

The paper presents a model for managing ED overcrowding that's based on the heart.  The ED is the heart, patients the life blood.  Three phases impact overall flow, preload, contractility and afterload.  This is a model of some value if you're sphere of control is ED centric - there are some good ideas about optimizing ED throughput.  There is a broad range of down stream factors that affect ED overcrowding:

The final phase, that of afterload, correlates to the need to be able to move patients on from the ED. This includes consideration of issues, such as ‘bed-block’ (where patients are unable to be moved onto ward beds or specialty areas), delays in inter hospital transfers, mismatches between admission and discharge times leading to late intrahospital disposition, and available community resources.