question: Which group in percent of commuters in Dallas in 2009 is smaller: carpooling or walking?
#1 return commuters in   Dallas in  2009 
#2 return #1 that are carpooling commuters 
#3 return #1 that are walking commuters 
#4 return percent of #2 
#5 return percent of #3 
#6 return which is the  lowest of #4 ,  #5