R help - May 2011 - How to process raw trip records to get number of persons per trip by vehicle

I have a large data set containing travel records for a para-transit 
system.  There is one record for each person transported, that contains 
the following information:

Vehicle.Id    Customer.Id    Trip.Date        TimeOn    TimeOff    Fare
W36               1                     2009.07.01    09:15        
09:53        3.75
W36               2                     2009.07.01    09:23        
09:57        3.75
W36               3                     2009.07.01    11:40        
13:06        5.45
W35               1                     2009.07.08    09:19        09:58 
        3.75
W36               2                     2009.07.09    09:43        
10:07        3.75
...

And I need to process it to end up one record per "trip" the vehicle 
makes, determining the number of passengers transported that trip.  
Something like the following:


Trip.Date        Vehicle.Id    Trip.Start    Trip.End    
Number.of.passengers    Total.Revenue
2009.07.01    W36              09:15         09:57            2        
                                 7.50
2009.07.01    W36              11:40         13:06            1        
                                 5.45
2009.07.08    W35              09:19         09:58            1        
                                 3.75
2009.07.09    W36              09:43         10:07            1        
                                 3.75


I can think of a procedure to process the data that is a very 
traditional algorithm type, but it doesn't make use of any of the R 
features.  Does anyone have any suggestions for how they would implement 
this analysis in R?


Walter Anderson