SAN JOSE — Despite the presence of an admittedly fatigued driver and a rain-soaked Highway 101, federal investigators have concluded that inadequate road markings were to blame for a disastrous January 2016 Greyhound bus crash that killed two and injured over a dozen others.

In a report presented Tuesday, the National Transportation Safety Board said the absence of reflective warning markers, preceding a gore point separating the carpool lane connector to Highway 85 from 101, made the bus driver think he was in the connector lane when he was actually heading straight into a concrete barrier.

Agency officials contend the crash was preventable.

“This crash did not have to happen because the barrier that the bus hit should have been visible, even in the bad weather, but it was not,’’ NTSB Acting Chairman T. Bella Dinh-Zarr said in a statement. “Moreover, the crash would probably have resulted in fewer deaths and injuries if the occupants had worn their seat belts.”

The ensuing violent crash upended the bus and caused two women to be thrown from the vehicle as it barrel-rolled onto the roadway. The ejected passengers, Maria De Jesus Ortiz Velasquez, 75, of Salinas, and Fely Olivera, 51, of San Francisco, died almost immediately.

The driver, Victorville resident Gary Bonslater, was injured along with 12 other passengers on the bus, which was carrying 21 people when the Jan. 19, 2016 crash occurred.

Caltrans, the agency responsible for maintaining the state’s highways, did not immediately respond to a request for comment.

An NTSB news release added that Caltrans “did not mark the gore with stripes or chevrons, which are often used to differentiate the gore from the roadway.”

While federal investigators noted that the darkness of the early-morning hour — about 6:37 a.m. — factored into the crash, the report made no mention of driver fatigue, an issue that gained resonance after Bonslater reportedly told investigators after the crash that he was fatigued and drank coffee during a stop about 20 minutes earlier in Gilroy, but that his memory of the crash was scattered.

A passenger also told assembled media at the crash site that he noticed the driver was struggling to stay awake just before the crash.

The NTSB made an array of recommendations stemming from its investigation, including the need for Caltrans to better track its work on roadway visibility projects, increase signage at the Highway 101-Highway 85 connector ramp, and better distinguish the gore point with visible and tactile road markers. The agency also recommended that Greyhound revamp its supervision of drivers and better enforce the use of seat belts by its passengers.

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More information from the NTSB investigation can be viewed at ntsb.gov/news/events/Pages/2017_sanjose_ca_BMG.aspx