Yes, but....
Continuing the downward trend of something like the past 2 decades. Then we can get into things like population density, gas prices, and weather.
Let's put it this way. Ontario enjoyed a sharper drop in the downward trend line than anywhere else.
That's quite a feat, especially given that Ontario was already one of the lowest, if not the lowest, jurisdiction in North America as far as fatality per km driven rates goes. It's relatively easy to improve when you're dealing with an abysmally poor record, but when your record is virtually the best in the pack, additional improvements usually become harder to achieve.
You can quibble and bring up things like weather, population density, but that is not unique to Ontario. Also, Ontario is a pretty big province. Once you get more than 30 km away from the Toronto city core, density starts to take on a sharp downward trend.
Bad weather is another factor that is hardly unique to Ontario. Besides, bad weather has little effect on the bulk of our driving. You still have to get to work, you still have to get to shopping and services. Goods still have to be shipped. Bad weather may have an effect on your trip to the beach, but there are still plenty of recreational travel that is weather-independent.
This is reflected in the actual gasoline consumption stats for Ontario that show a drop of only 1% in the volume of gasoline sold in Ontario for 2008, and part of even that little drop might be attributable to a move to more fuel-efficient vehicles. Also, that drop in volume rebounded back and then some in the very next year.
Gross sales of gasoline (2005 to 2009, thousands of litres) 15,576,477 15,507,629 15,840,468 15,667,959 15,849,943
The effect of bad weather in reducing traffic volume was negligible. Offsetting that however was the increased risk of crash that comes with driving on wet roads with reduced traction and visibility because of rain.
And gas prices is somehow an Ontario thing? The same high oil prices that raised our fuel prices were also a factor in raising fuel prices in every other market in North America. Where is their corresponding drop in fatality rates to match what Ontario enjoyed?