The claim that the Prunty County (PC) should undertake the same kind of road improvement project as Butler County (BC) to improve the safety of PC's roads seems somewhat reasonable at first glance. After all, the arguer does offer some relevant evidence, and the assumptions weakening this argument are not without any merit. However, three important concerns which he/she fails to take into account may undermine the argument seriously.
In the first place, lacking more specific information about the results that the changed speed limit lead to, it is impossible to make an informed conclusion. As the arguer mentioned, most drivers are exceeding the new speed limit, then there are still some drivers are obeying it which may obviously improve the safety of the roads. Meanwhile, he/she doesn't give the clear statistics, the description about the decline of accidents rate is too vague to allow any wise judgment based on it.
In the second place, the arguer unfairly assumes that the same measure and improvement taken in BC will literally have the same effect in PC. There may be several other reasons lead to the lower accidents rate in BC, such as less population, better traffic signs and driving skills, it is even perhaps there are fewer jobs in BC in the past year, so people once lived there had to move out to find another job, hence the accidents surely fewer than before. Any of the above scenarios, if true, would render this analogy a completely false one.
What further weakens the argument is without knowing where did the news that the accidents rate has dramatically declined in BC come from, we cannot accept the arguer's presumptuous recommendation. While this may be true in most cases, it is equally possible that the council of BC lied to the mass in order to attract more people to buy houses or pay a visit there. Then, how can the arguer make any convincing conclusion based on the false data?
As it stands, this argument suffers from three critical flaws. To strengthen it, the arguer would have to demonstrate that the former limit on speed really didn't bring any fruit to PC. Furthermore, he/she must provide enough and acceptable evidence to rule out all the above-mentioned possibilities that might undermine the argument.