Third-Party Repairs

P was injured when his car was struck by D's train while crossing D's railroad tracks. After the accident the State Highway Department installed signal lights at the crossing. Psues D. At trial, P offers evidence of the Highway Department's remedial measures. D objects. What ruling and why?

The repair in this case was not made by the defendant but by a third party. Is evidence of the repair relevant to the dangerous nature of the crossing, which the railroad could have done something about? Is the policy of encouraging potential defendants to make repairs applicable in cases where the repairs are made by someone other than the defendant?