Actually, it may be an instance of a "tragedy of the commons" but I think the most strategically optimal move for a state when there are 49 others is to ban it and let "sucker" states do the testing, and then immediately legalize it as soon as it shows promise.
Just like how I never upgrade to a new software version right away, letting the other "suckers" test it in production for me, creating value for me at their expense with no repercussions whatsoever, since the delay is very small.
Another strategically effective move might be to charge corporations an appropriate fee to capture back the value of the data they are collecting by experimenting on public roads. Given how valuable driverless technology could be, the fees could be large.