Just trying some napkin math...

Some very surface-level searching shows someone claiming a total societal cost of ~$7k per deer collision.

Supposing it's a $15m construction and could last 30 years without major maintenance, then it needs to stop ~71 events per year to "pay for itself".

To be fair, that is the cost of collisions rather than any near-misses and traffic problems, or the less-quantified ecological cost.