Last week’s Q&A with Rick Molchany, Lehigh County’s director of general services, who offered some insight into the upcoming closing of the Coplay-Northampton Bridge, drew a huge response from readers.

Many took to social media, posting angry-faced emojis and comments of exasperation. Some sent emails, filled with examples of other projects done in a more timely manner.

Most asked that one more question be asked:

Why in the world was this new bridge going to take three years to complete?

According to Molchany, there are many reasons for this time projection.

There are existing utilities on the bridge that need to be temporarily relocated before the bridge demolition can even begin.

The demolition of the existing structure, which dates back to the 1930s, must be performed in a controlled manner to protect the portions of the existing abutments and pier footings that will remain in place.

The task of demolishing the old bridge and constructing the new one is constrained by the work being performed over the Lehigh River, adjacent to Norfolk Southern Railroad - which requires flagging - and over the Ironton Rail Trail - which requires the work to be performed using multiple construction stages.

Some construction tasks can be performed concurrently, but others need to be performed sequentially.

Pouring of the concrete piers and concrete bridge deck will be done in phases, Molchany said, and each phase requires a concrete-curing period before the next phase can begin.

Timing of the concrete placement for the bridge deck is a significant consideration, as placement in the winter requires that the deck be heated from the underside, something that is very costly and difficult to accomplish in a river environment - and, thus, is usually avoided.

There are instream work restrictions between April 1 and June 30 annually.

“Although each bridge is unique, history has shown that the construction duration for bridge replacement projects - with bridge lengths in the range of 300 to 1000 feet and with four to eight spans, over railroads and/or rivers or streams - have generally taken three years to construct,” Molchany said.

The cost of the new bridge is estimated at $33.5 million. A dedication ceremony is planned for 2020.