Hi,
1) Calculate the number of households
2) Calculate the number of vehicles (% households owning the vehicles)
3) Assume the lifetime of a car (let's say 10 yers) and the av. change of ownership rate (2 times in 10 years). Thus the replacement rate will be 1/5 cars per year
P.s. Don't forget about commercial vehicles. You can use personal experience to say that every 10th vehicle is commercial. Apply different replacement rate for them
Best
