The 12-mile (19-km) bridge is the only direct connection between the Crimean peninsula and Russia, making it a key strategic target in the ongoing conflict between Russia and Ukraine. Prior to its completion by Russia in 2018, the peninsula was only accessible by airplane or ferry.

According to the Investigative Committee of Russia, the country’s main federal investigating authority, the blast was caused by a truck bomb. Its investigation into the incident is ongoing although multiple Russian officials have blamed Ukrainian intelligence services in public comments.

Marat Khusnullin, Russia's deputy prime minister for construction and regional development, posted photos of bridge repairs on his Telegram channel on Oct. 12 and provided a progress update.

He reported that one barge had been moved into place earlier in the week and a second was expected to be on the site when weather allowed. “In total, 250 people and 30 pieces of equipment are already working on the bridge!” Khusnullin wrote. 

On Oct. 13, the Russian cabinet issued a decree identifying construction firm Nizhneangarsktransstroy L.L.C., based in Irkutsk, as handling the repairs and ordering all work on the bridge to be complete by July 1. The decree says Nizhneangarsktransstroy can use other contractors for the repairs but the company must complete at least half of the designated amount of work. According to Khusnullin, the main reconstruction work is expected to finish by the end of the year.

"Technologies have been found to dismantle the existing destroyed bridge supports,” Khusnullin told Russia's news agency. “I can say that the first supports of the new bridge have already been manufactured at factories and are going to the Crimean bridge.”

Construction of the $3.7-billion bridge began after Russia annexed Crimea, formerly Ukrainian territory, in 2014. Russian construction company Stroygazmontazh (SGM Group) began work in 2016 and the bridge was opened to traffic two years later. The bridge, the longest in Europe, consists of four lanes of vehicle traffic with a separate double-track railway.

Brian Brenner, principal bridge engineer at U.S. consulting firm Tighe and Bond, said the extent of the damage to the roadway bridge may have been exacerbated by the structure's design. The continuous span construction of the bridge's roadway portion likely resulted in more damage than if the structure had been constructed using simple spans that would have isolated the explosion impact, he said.

An additional factor was the decision to construct the bridge with non-redundant steel girders and floor beams instead of a multi-girder framing system.

“Non-redundant structural systems can fail catastrophically, which is what looks like happened to the highway bridge,” he explained. “A multi-girder system has additional load paths that can limit the degree and amount of failure.”

Assessing damage to the concrete piers on the roadway bridge and rail bridge, both consumed by fire, would be difficult to determine by photographs alone, Brenner said. Ensuring the integrity of piers will be critical to ensuring traffic safety on both bridges since, if they are structurally compromised, heavy loads could lead to failure, he added.

While completing repairs by July might be possible, Brenner said it would be significantly complicated by the onset of winter. Concrete work would require special cold weather procedures and access would be hampered by cold and stormy weather.

Since the explosion, train traffic on the rail bridge had been halted to clear damaged rail cars. Russian officials said trains were able to operate on the line although it was not clear if rail traffic had resumed. Freight traffic on the roadway, which had been prohibited after the explosion, would be allowed to resume over the weekend, officials told Russian state-owned news agency RIA Novosti, although inspections would be required.

“Loaded vehicles will either be fully inspected, or they will go by ferry, or they will travel along routes through new territories,” Khusnullin told the news agency.

While western security services have refrained from attributing blame for the blast, independent researchers examining the available evidence suggest the truck explanation is probably the most likely. Open-source intelligence efforts have provided an additional viewpoint in analyzing the significant amount of digital data being produced from the ongoing conflict in Ukraine.

While concrete evidence of what caused the blast may not be available, open-source intelligence (OSINT) researcher Oliver Alexander, who has examined the available evidence, said the truck theory “does not have a large piece of photographic evidence pointing against it.”