The Taiwan Transportation Safety Board (TTSB) released the final report on the investigation of an electric vehicle hit the outer guardrail on southbound Huwei section of Freeway No. 1 and fell onto the ground then caught fire.

At 21:11 on June 6, 2024, a private passenger car (hereinafter referred to as the vehicle) carrying one driver and two passengers crashed into the outer metal guardrail on the Huwei section of Freeway No. 1 southbound at 237K+520. It fell into the empty lot next to Yunlin County Township Rural Highway Yun No. 76 below Freeway No. 1. The vehicle broke into two parts, and the front half caught fire. The accident caused the death of one passenger in the right rear seat and minor injuries to the other two occupants.

In accordance with the Transportation Occurrence Investigation Act, the Taiwan Transportation Safety Board (TTSB) is the independent transportation occurrence investigation agency responsible for conducting the investigation. The investigation team also included members from the Ministry of Transportation and Communications (MOTC), the Freeway Bureau of MOTC, the National Highway Police Bureau, the Yunlin County Fire Department, and Tesla Motors Taiwan Limited.

The draft of this investigation report was completed in July 2025 and, according to procedures, sent to relevant agencies (institutions) for their opinions. The investigation report was published after review and approval by the 78^th Board Meeting on September 23, 2025.

Ⅰ. Investigation Findings

Findings Related to Probable Causes

1. The driver was operating the vehicle at a speed exceeding 200 kilometers per hour. Under such high-speed conditions, in addition to the reduced tire grip and diminished vehicle controllability, the dynamic vision and field of view of the driver, as well as perception and reaction time, were also adversely affected. These factors collectively impaired the driver’s ability to respond to sudden situations. Immediately prior to the accident, the driver attempted to evade a vehicle ahead, which may have led to improper maneuvering through untimely reaction and excessive steering.
2. The vehicle may have veered off to the left or right due to excessive steering by the driver, causing the center of gravity of the vehicle to shift continuously, ultimately placing the vehicle in an unstable posture, which led to skidding and loss of control. The vehicle then collided with the outer guardrail and ran off the road, causing the death of the passenger in the right rear seat.

Other Findings

1. At the time the vehicle separated into front and rear halves, the seat belt buckle and latch plate were located in the front half of the vehicle, while the retractor and anchorage of the seat belt were situated in the rear half. The forces generated at the moment of impact caused the seat belt to be subjected to strong tension, resulting in compression at the buckle area and rupture around it. The load exerted on the seat belt exceeded its tensile strength, leading to the tearing of the strap. Consequently, the passenger in the right rear seat was no longer restrained and was ejected from the vehicle.
2. When the vehicle was travelling approximately 500 meters upstream from the accident site, its speed reached between 200 and 216 kilometers per hour. The vehicle subsequently struck the Jersey barrier, resulting in the breakage of the vehicle body. At the time the vehicle veered off the freeway, its speed was between 96.5 and 101.6 kilometers per hour. Since the vehicle body had absorbed most of the energy during the separation process, it is assessed that the actual vehicle speed at the moment before the collision was higher than the calculation result stated above.
3. Under the side-impact testing standards of both the United Nations and the United States, the speed for testing is 32 kilometers per hour—significantly lower than the speed at which the vehicle struck the Jersey barrier. Even if the vehicle had met the United Nations and United States testing standards, such compliance would not guarantee that the vehicle could maintain structural integrity following the collision.
4. The point of impact on the vehicle was the rear door area, corresponding to the connection between the battery structure and the motor structure, as well as the alternation and welding point of the chassis material. Under the combined effect of vehicle speed and the inertia of the vehicle mass, the vehicle was unable to withstand the collision force after striking the Jersey barrier, ultimately resulting in structural failure of the body and its separation into two halves. In addition, in the accident that occurred on May 7, 2023, in Xitun District, Taichung City, the vehicle's speed was likely comparable to that in this case. In both incidents, the object of impact was a concrete Jersey barrier, and both vehicles fractured into two parts, with the fractures occurring in the rear portion of each vehicle.
5. Upon examination of the vehicle body damage, the point of impact with the Jersey barrier was located at the left rear side of the vehicle, which was also the connection point between the end of the high-voltage battery pack and the rear motor. As no batteries were installed in the rear section of the vehicle body, combustion did not occur there. However, the high-voltage battery pack in the front section of the vehicle body was subjected to external compression during the collision, causing deformation of the battery casing and intrusion into the internal battery cells. This resulted in the rupture of the separator between the positive and negative electrodes, leading to contact between the electrodes and a short circuit. When the vehicle subsequently veered off the roadway and struck the ground, the damage to the battery was further exacerbated, ultimately starting a fire.
6. Both the event data recorder and the onboard computer of the vehicle were destroyed due to the post-crash fire. Apart from the system warning records during the accident and the dynamic data for the period up to 1 minute prior to the collision with the guardrail provided by Tesla, no additional pre-crash data related to the vehicle could be retrieved.

Ⅱ. Safety Recommendations

　　In the draft of this investigation report, the proposed initial safety recommendation to the Freeway Bureau, Ministry of Transportation and Communications was as follows:

　　Review and strengthen management measures to prevent serious overspeeding on freeways, and coordinate with the National Highway Police Bureau in continuously assessing enforcement effectiveness.

　　The actions taken by the MOTC and the Freeway Bureau in response to this recommendation, including completed or ongoing actions taken, are detailed in Section 4.2 of this investigation report. Therefore, this recommendation is not reiterated in the final report.

　　In the draft of this investigation report, the proposed initial safety recommendation to the National Highway Police Bureau was as follows:

　　Review and strengthen enforcement measures to prevent serious overspeeding on freeways, and continuously assess and improve enforcement effectiveness.

　　The actions taken by the National Highway Police Bureau in response to this recommendation, including completed or ongoing actions taken, are detailed in Section 4.2 of this investigation report. Therefore, this recommendation is not reiterated in the final report.

Full Final Report in Chinese is available for download at https://www.ttsb.gov.tw

Ya-Ting Chang, Director

Secretary Office

Tel: +886-2-7727-6210

E-mail: yating@ttsb.gov.tw

Richard Jih, Investigator-In-Charge

Highway Occurrence Investigation Division

Tel: +886-2-7727-6272

E-mail: richard@ttsb.gov.tw