On the one hand, there is still too much needless loss of life on US roads every year, and the data geek in me wants to believe that gathering more data about the events immediately surrounding an accident might be helpful in designing safety systems that would help prevent future accidents.
On the other hand, this adds some cost to the price of each vehicle (probably several hundred dollars today, though that cost probably drops significantly once these EDRs are built in large quantities), gives "big brother" yet another look over your shoulder, and -- given that to enable the emergency response feature the vehicle has to have a wireless connection, which means its location can be tracked at all times -- means that every vehicle can be tracked and located at any time, not just by the government, but also potentially by criminals, advertisers, or anyone else you'd want to avoid.
Given how very few vehicles relative to the millions sold each year will be in accidents from which useful EDR data might be recovered, I'm not sure the mandate and investment is worth it.
I'll go out on a limb and suggest that the best investment in increased road safety would be increased training and licensing standards for drivers. If we were to raise the bar similar to European driving standards, we might achieve the same intent at much lower cost.
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