1. A computer-implemented method for determining estimated traffic flow information for roads based on data samples that are reported by vehicles traveling on the roads and that include information regarding the travel of the vehicles, the method comprising: receiving indications of multiple road segments of one or more roads; generating probability distributions that indicate, for each of multiple distinct observed quantities of vehicles on a road segment during a period of time, probabilities for arrival rate volumes of vehicles at the road segment given the observed quantity of vehicles; and for each of multiple periods of time, receiving information related to current traffic conditions of the multiple road segments during the period of time, the received information including a plurality of data samples for the period of time that each are reported from one of multiple vehicles and reflect a reported speed of the one vehicle at a reported location on one of the road segments at a reported time during the period of time, the multiple vehicles being a subset of all vehicles traveling on the road segments during the period of time, the received information further including a plurality of additional data samples for the period of time that each are reported from one of multiple traffic sensors monitoring the multiple road segments and reflect a reported speed based on one or more speed readings for one or more vehicles at a location on one of the road segments for one or more reported times during the period of time; for each of the multiple road segments, automatically estimating traffic flow information of all vehicles traveling on the road segment during the period of time by, identifying a group of multiple data samples for the road segment for the period of time, the multiple data samples being from at least one of the plurality of data samples and the plurality of additional data samples; determining a quantity of vehicles to which the data samples of the group correspond, the corresponding vehicles being a subset of all the vehicles traveling on the road segment during the period of time; determining a most probable traffic arrival rate volume at the road segment of all the vehicles traveling on the road segment during the period of time, the determining of the traffic arrival rate volume being based at least in part on the generated probability distribution for the determined quantity of vehicles that reported the data samples of the group; determining a most probable traffic density for the road segment so as to represent a total quantity per unit of distance of all the vehicles traveling on the road segment during the period of time, the determining of the traffic density being based at least in part on the determined traffic arrival rate volume for the road segment during the period of time; and determining a most probable percentage traffic occupancy of at least one point on the road segment by all the vehicles traveling on the road segment during the period of time, the determining of the percentage traffic occupancy being based at least in part on the determined traffic density; and using at least some of the determined traffic arrival rate volumes, traffic densities, and percentage traffic occupancies for the period of time to facilitate future travel on the one or more roads, so that estimated traffic flow information is determined for road segments based on data samples reflecting actual vehicle travel on the road segments.