I think it may work better if you made it like a best and fairest vote were everyone that attends a trip votes for their top 3 with a 3,2,1 vote with no comments and the vote being secret. Not about who gets up that hill but who helps out......
My opinion with that is, some will try to do something they are normally not comfortable with doing. Have seen this happen on a fair few ocassions that end very 'pear shaped'....
Again, rather than vote on 'driver ability' as such, give a good rating to those who are prepared to help out on the day, give advice where necessary, & have the 'balls' to say no to something they are not comfortable with.