Minimum supervised driving hours (MSDH) are a key component of Graduated Driver Licensing (GDL) policy. GDL has been shown to reduce motor vehicle accidents, but its optimal design is far from clear. Exploiting two discrete MSDH changes in New South Wales (the largest state in Australia), we estimate causal effects of various MSDH options, providing evidence on driver safety under different regimes. Increasing MSDH from zero to 50 h lowered the risk of a motor vehicle accident in the first year of unsupervised driving by around 23%. Further increasing the mandate to 120 h had no additional benefit.
Kettlewell et al. (2026) studied this question.