Assignment: Summary leads

http://seattletimes.nwsource.com/html/traffic/2009873777_520tolls16m.html
Motorists won't have to pay tolls on the Highway 520 floating bridge until as late as June 2011, instead of October next year.

This lead mentions who (motorists), what (tolls), where (520 floating bridge) and when (June 2011 and not October 2010). It gives the most prudent information available because in this case why isn't as important because it cannot be accurately described in a one sentence lead. Why is described in the nut graph and attributed to the complications of starting the tolls, in part due to the high cost of installing the tolling methods.