Here are various reports from past or on-going projects that ISA Software is involved in.

Airspace complexity for regulatory purposes - Part II
Airspace complexity for regulatory purposes - Part I
DMEAN - Benefit assessment of operational Use Case 3
A complexity study of the Maastricht Upper Airspace Centre
ATM contrail mitigation options - Environmental study
Enhanced flight efficiency indicators
Flight efficiency and its impact on the environment
Traffic complexity indicators and sector typology analysis of US and European centres
Capacity Shortfalls in Europe