It's been just over three weeks since the sidewall of a rail bridge came crumbling down near Syracuse's Mission District.

SU engineering professor Riyad Aboutaha said that the bridge showed physical deterioration. He says that's primarily due to corrosion of steel bars in concrete. 

In this case he says most of the deterioration happened near the top of the bridge pier. That's what supports those wall beam elements.

The bridge had been inspected in May of 2017. But, he says older bridges may need to be checked more frequently.

"In this case it was obvious that it was too much delayed maintanence where the bridge shows too much signs of deterioration. That doesn't occur over a year or two. It occurs over many years."

That 2017 inspection showed that there was spalling and cracking in the concrete and that rebar was showing.

Inspections were done on the other rail bridges throughout the city following the collapse. The engineers said they found no immediate structural concerns.

Rail service resumed Monday.