Based on the two documents “226718 NIAO Major Capital Projects_FINAL LW RES Complete.pdf” and “NI Audit Office Report – Major Capital Projects (follow-up).pdf”, here are the projects ranked by largest cost overruns:

1. A5 Western Transport Corridor
   Cost overrun: £901 million
   Original estimate: £799m
   Current estimate: £1.7bn
   Main causes: Legal challenges, planning issues, funding constraints, environmental assessments
2. Regional Children’s Hospital
   Cost overrun: £366.6 million
   Original estimate: £223m
   Current estimate: £589.6m
   Main causes: Design changes, changes in guidance/legislation, inflation, market conditions
3. Strule Shared Education Campus
   Cost overrun: £197.4 million
   Original estimate: £168.9m
   Current estimate: £366.3m
   Main causes: Procurement issues, limited market interest, lack of precedent for benchmarking costs
4. Belfast Transport Hub
   Cost overrun: £131.1 million
   Original estimate: £208.9m
   Current estimate: £340m
   Main causes: Extraordinary inflation, market conditions
5. Energy Centre at Royal Victoria Hospital
   Cost overrun: £117 million
   Original estimate: £42.5m
   Current estimate: £159.5m
   Main causes: Not specifically detailed in reports
6. Ulster University Greater Belfast Development
   Cost overrun: £103.8 million
   Original estimate: £254m
   Current estimate: £357.8m
   Main causes: Construction defects, contractor administration, funding issues
7. Critical Care Centre
   Cost overrun: £60.8 million
   Original estimate: £95m
   Final cost: £155.8m
   Main causes: Construction quality issues, changes in standards/guidance
8. Cityside HCC
   Cost overrun: £54.4 million
   Original estimate: £71.4m
   Current estimate: £125.8m
   Main causes: Not specifically detailed
9. Ulster Hospital Phase B Main Build
   Cost overrun: £84.4 million
   Original estimate: £195.3m
   Final cost: £279.7m
   Main causes: Not specifically detailed
10. Maternity Hospital
    Cost overrun: £39.9 million
    Original estimate: £57.2m
    Current estimate: £97.1m
    Main causes: Delays from COVID-19, changes in standards/guidance, complexity of working on live hospital site

The report highlights systemic issues across projects including:

• Funding constraints and uncertainty
• Legal challenges and planning issues
• Limited interest from construction industry
• Construction quality issues
• Changes in standards and guidance during projects
• Market conditions and inflation
• Lack of early stakeholder engagement
• Procurement process issues
• Capacity and capability gaps in project management

The reports emphasize that while individual factors contributed to specific project overruns, there are fundamental weaknesses in Northern Ireland’s commissioning and delivery system for major capital projects that enable these substantial cost and time overruns to continue occurring.