Not all powerchairs are specifically designed to incorporate sufficient strength to properly protect the occupant in the event of a collision. To maintain your safety it is advisable to transfer from your powerchair seat to a vehicle seat.
This is often not practical.
In New Zealand the LVVTA (Low Volume Vehicle Technical Association) recommends that wheelchairs used in vehicles where the occupant remains seated be designed to be safe and adhere to international disability transport standards. Refer to LVVTA 45-60(02) Disability Transportation Systems, in particular section 2.6(i)(a)(i)-(iii).
All TA powerchairs comply with this NZ safety standard and, in particular, international standard ISO 7176-19 (wheeled mobility devices for use as seats in motor vehicles). TA Service have crash tested their chairs to maximise your safety and minimise your injury risk in the event of a collision.
If you are not sure ask your disability specialist for evidence from the manufacturer, specifically crash test certificates and crash test videos for your confidence.