There were almost 16,000 casualties in 1968, compared to just under 13,700 in 2004 and 8,208 in 2014.
Road safety charity Brake welcomed the Welsh government figures but called for more to be done, including a 20mph speed limit in all urban areas.
The Welsh government is introducing 20mph limits outside 41 schools.
Philip Goose of Brake said: "It is obviously good news that road casualties across Wales are falling.
"However, this is in stark contrast to deaths and serious injuries rising across the UK and, despite reductions, every single one of these deaths is avoidable and a tragedy with lifelong consequences for families and loved ones left behind."
The Welsh government's scheme will be on a part-time basis at schools on main roads and the Â£4.5m programme will run for three years.
Roads outside eight other schools which were trialled earlier this year are having the limits made permanent.
Mr Goose added: "Installing temporary measures outside schools is certainly a start but installing mandatory 20mph limits outside schools, as well as where people live and work, would go a long way to increasing the safety of local people."
The Welsh government said statistical evidence showed a reduction in injuries in 20mph zones and it was committed to reducing casualty figures through enforcement, education and infrastructure.
A spokesman added: "This includes our road safety framework for Wales, our safer routes in schools policy and we have announced part-time 20mph speed limits for nearly 50 schools on trunk roads.
"It is encouraging to note the reduction in casualties, however, road safety is everyone's responsibility so it is vitally important all road users remain vigilant to reduce collisions."
The number of people killed or hurt on Welsh roads is at its lowest level since records began, with a 40% drop in the last 10 years alone.