For major rail upgrade projects, what is the best way to assess whether early contractor involvement genuinely reduces long-term programme risk?

For major rail upgrade projects, what is the best way to assess whether early contractor involvement genuinely reduces long-term programme risk?

I’m reviewing different procurement approaches and trying to understand how to measure the real value ECI brings in terms of cost certainty, schedule resilience and stakeholder coordination. Any insights or examples from recent projects would be really helpful.