This paper investigates the accuracy of accumulation estimation at different urban scales, mainly link and network levels. Different methods are compared depending on sensor types, probe vehicles or loop detectors, and historical data availability. Probe vehicles can provide an accurate estimation of the average travel times but only for a given vehicle sample. So, we resort to loops to calculate the fishing rate and scale up the observations to all vehicles. The fishing rate is the ratio of probes that are detected at the loop locations over the loop flow. Accurate accumulate estimation at the link level can only be obtained when probes and loop data are available in real-time. Methods based on spatially aggregated fishing rates when probe data are available but not loops show better results, but the errors are still significant at the link level. It is possible to obtain accurate accumulation estimations at the network level when combining loop and probe observations, even if few links capture both data sources. It requires applying proper aggregation technics and a careful definition of fishing rates at this scale.