Abstract This paper uses an econometric meta-regression analysis framework to examine how the mean percentage cost overruns (MPCOs) of transportation projects reported in the literature vary by study specific characteristics, such as whether it is a road or rail project, the world region where the study was conducted; and the year of publication of the study. The motivation of the study is that there are no other studies in the literature on MPCOs of transportation projects using meta-regression analysis; a method well respected in other fields for summarizing findings from different studies. The data used comprise 127 data points retrieved from 48 studies from across the continents. The results show that (1) cost overruns rather than underruns are prevalent across all types of studies, and the typical cost overrun is, on average, 34% regardless of the transportation infrastructure under consideration; (2) recent studies show significantly lower MPCOs as compared to earlier studies; (3) published studies in scientific journals or conference proceedings show higher MPCOs than unpublished reports; (4) in comparison with Asian studies and those of the rest of the world, European and North American studies show significantly lower MPCOs, but Australian studies are not significantly different; (5) road projects show significantly lower MPCOs than rail projects regardless of the region of study; and (6) European and North American roads show higher MPCOs than rails in Asia and the rest of the world. We conclude that the magnitudes of MPCO results from individual studies should not be generalized as the study specific characteristics matter. Insights offered by this study can, therefore, serve as a reference when reporting results from individual studies.