IMPACT OF FREEWAY GRADE ON PRIVATE SECTOR TRAVEL TIME DATA BIAS

摘要

MAP-21, the current surface transportation authorization, mandates that transportation agencies establishand report performance measures for system performance. Many agencies are likely to utilize privatesector travel time and speed data to address these performance measure requirements. It is commonlyunderstood that many of these private sector data sources use GPS probe data generated by commercialvehicles as a primary input. Although past studies of private sector data quality support its use forfreeway performance monitoring, nearly all past studies focused on urban roads with relatively flatgrades.Commercial vehicle speeds can deviate substantially from passenger vehicles in mountainousterrain, particularly while traveling uphill. There is therefore a need to investigate the impact of roadwaygrade (terrain) on private sector data quality, especially on rural Interstates with mountainous terrain. Thisresearch compares data from a private service provider with Bluetooth benchmark data for I-77 insouthwestern Virginia to determine whether there is a bias in private sector data that is correlated withroadway grade. The results show that although the private sector data’s speeds were consistently underpredictedslightly relative to benchmark speeds, no strong correlation was found between the magnitudeor length of grade and speed bias. It is therefore concluded that private sector data can do a reasonablygood job of estimating overall freeway performance in mountainous terrain for MAP-21 reportingpurposes.TRB