The aim of the article was to present the results of road tests on running up buses trucks and truck-tractors with semi-trailers. In the years 1999 – 2013 over 115 vehicles have been tested. Selected results of road tests compared with simulations in the computer program. The presented materials and analyses approximate the problem of estimating the dynamic parameters of buses and trucks under changing loads and external conditions (rolling resistance, elevations, air) as well as simulation reliability of computer programs available to court experts in road accident reconstruction.