​​​​On Thursday, February 11, 2021, about 6:00 a.m. central standard time, a multivehicle crash occurred in the southbound toll lanes of Interstate 35 West (I-35W), in Fort Worth, Tarrant County, Texas. The crash sequence began on an elevated portion of the roadway near the exit to Northside Drive and ultimately involved 130 vehicles. The posted speed limit on the I-35W toll lanes was 75 mph.

In the days before the crash, the area had experienced 36 consecutive hours of below-freezing temperatures. In anticipation of forecast freezing rain and sleet, North Tarrant Express Mobility Partners Segments 3 (NTEMP S3), which was responsible for operations and maintenance on the I-35W right of way at this location, pretreated the traffic lanes with a liquid brine solution. NTEMP S3 applied the solution to the two southbound toll lanes about 44 hours before the multivehicle collision occurred. On the morning of February 11, the first measurable precipitation occurred between 1:34 and 2:10 a.m.; light mist and fog were reported from 2:53 to 4:53 a.m. Before the crash, dynamic message signs managed by NTEMP S3 along the southbound toll lanes were displaying the following message to drivers: “ICY CONDITIONS EXIST/PLEASE USE CAUTION.”

The crash event began about 6:00 a.m., when several vehicles in the southbound toll lanes slid on the elevated roadway and struck the concrete barriers beside the toll lanes. As approaching drivers encountered the vehicles involved in these initial crashes, they were unable to stop on the icy roadway, leading to secondary crashes. As a result of the crash event, six people were fatally injured. Four of the fatally injured people remained inside their vehicles; two were struck on the roadway after they had exited their vehicles.

We undertook this focused investigation to examine the inclement weather road maintenance performed before the crash on the toll lanes of I-35W. During the investigation, we also identified the need for technological measures to help drivers and vehicles respond appropriately to inclement weather conditions.

We found that the surface of the elevated roadway in the area of the crash was icy, which made drivers lose control of their vehicles, which then slid into road barriers and other vehicles. Although NTEMP S3’s pretreatment of the roadway before the storm was reasonable, its roadway monitoring process was deficient because it failed to detect that the elevated portion of I-35W required additional  deicing treatment on the morning of the crash when precipitation arrived in the area. If environmental sensor stations had been installed near the crash location, NTEMP S3 would have had additional data at its disposal, which might have helped it to detect that the location needed additional deicing treatments before the crash. Greater deployment and use of environmental sensor stations, used widely nationwide, would enable more efficient detection and monitoring of roadway conditions, as well as better responses to environmental events, likely reducing crashes and injuries during inclement weather.

​We also found that the training that NTEMP S3 provided its employees was insufficient to prepare them to monitor roadway conditions effectively during winter weather events. Coordination between the Texas Department of Transportation (TxDOT) and contracted entities, such as NTEMP S3, on best practices for training employees responsible for snow and ice control would help ensure consistent use of effective procedures by all entities responsible for treating the roadway during inclement weather.

Finally, we found that, had drivers been traveling slower, they would have had more time to react and possibly avoid the crashed vehicles ahead. Reduced speeds would also have lessened the severity of the crashes once the vehicles began to slide on the icy road. Had technologies such as variable speed limit signs and speed safety cameras been used, drivers might have been more likely to slow to a speed appropriate for the conditions. In addition, connected vehicle technology, if installed on at least some of the vehicles involved in the crash, could have provided information about the stopped vehicles in the roadway once the crashes began to occur, so that approaching drivers might have been alerted to the imminent hazard and might have avoided or mitigated secondary crashes.

The NTSB determined that the probable cause of the multivehicle crash in Fort Worth, Texas, was ice accumulation on the surface of the elevated roadway, which made drivers lose control of their vehicles, which then slid into road barriers and other vehicles. Contributing to the unsafe roadway condition was the failure of North Tarrant Express Mobility Partners Segments 3 to effectively monitor and address roadway conditions along Interstate 35 West during and after periods of freezing rain and mist. Contributing to the severity of the crash outcome​ was drivers traveling at speeds too fast for the winter weather conditions.
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​As a result of this investigation, the NTSB issued three new recommendations to the state of Texas and reiterated five recommendations. We issued a recommendation to the state of Texas to implement a statewide plan to install environmental sensor stations in priority locations to enable timely response to hazardous road conditions during inclement weather. We also issued a recommendation to the state of Texas to provide a comprehensive winter weather training program to private and state-regulated toll facilities so that they can train their employees using the program. Finally, we issued a recommendation to the state of Texas to enact legislation to allow TxDOT to install variable speed limit signs on Texas roadways. ​​

We reiterated Safety Recommendation H-22-1 to the US Department of Transportation to implement a nationwide deployment plan for connected vehicle technology that resolves issues related to interference, ensures sufficient spectrum, and defines the communication protocols to be used. We reiterated Safety Recommendations H-13-30 and -31 to the National Highway Traffic Safety Administration to develop minimum performance standards for connected vehicle technology and require use of this technology. We reiterated Safety Recommendation H-22-6 to the Federal Communications Commission to implement appropriate safeguards to protect vehicle-to-everything communications from harmful interference. Finally, we reiterated Safety Recommendation H-17-31 to the state of Texas to amend current laws to authorize state and local agencies to use automated speed enforcement.