It wouldn't be logical that they would. The evidence shows he was going in excess of 70MPH when he blew the stop sign. There are warning signs before stop signs, that also has to be considered. The area at the intersection is flat also, the intersection was not hidden.
The jury would have to come to the conclusion that it was reasonable to miss all the warning signs and fly through the intersection at 70+ MPH.
More than just the accident, there are several questions that need to be asked about this incident. One is these is that Janklow was driving a car owned and insured by a third party. Under Congressional rules, members of Congress cannot take gifts. Clearly, using someone else's car and driving under their insurance is a major violation of House ethics rules.