using the geh statistic avoids some pitfalls that occur when using simple percentages to compare two sets of volumes. this is because the traffic volumes in real-world transportation systems vary over a wide range. for example, the mainline of a freeway/motorway might carry 5000 vehicles per hour, while one of the on-ramps leading to the freeway might carry only 50 vehicles per hour (in that situation it would not be possible to select a single percentage of variation that is acceptable for both volumes). the geh statistic reduces this problem; because the geh statistic is non-linear, a single acceptance threshold based on geh can be used over a fairly wide range of traffic volumes. the use of geh as an acceptance criterion for travel demand forecasting models is recognised in the uk highways agency's design manual for roads and bridges the wisconsin microsimulation modeling guidelines, the transport for london traffic modelling guidelines and other references.