Is there any statistics about the average widths of cars?
I don't believe there is any statistic containing information about widths of cars, but as Solar Mike noticed, you can compile such statistic by the information provided by car manufacturers for individual cars.
For example, I used to have a 2011 Toyota Yaris. Its width is 1695 mm according to Wikipedia. Now I have a 2016 Toyota RAV4 hybrid that is 1845 mm wide. Because of the 360 degree camera view, parking the 1845 mm wide RAV4 is not much harder than parking the 1695 mm wide Yaris. I believe most cars are between these extremes, although quite notably Tesla cars are wider than even RAV4. For example, Tesla Model S is 1964 mm wide. Tesla Model X is even wider: 2017 mm. I wouldn't want any Tesla car for this reason in my narrow parking space.
In general, you can expect SUVs to be slightly wider than regular comparable cars for the reason that SUVs have greater height and thus would have higher probability of rolling over during hard cornering. Thus, this risk is somewhat reduced (but not completely mitigated) by making the SUV wider than the regular car.