Abstract: The influences of the relative distance, burial depth, soil weight, internal friction angle and cohesion on the critical load are investigated by deriving the critical load of the plastic zone depth of the two-line immediately adjacent track beds developed to 1/4 of the plate width. The critical loads are compared with the ultimate bearing capacity obtained from finite elements to illustrate the differences in the allowable design values for the bearing capacity of road substrate foundations at home and abroad. The design analysis is carried out for the track bed of a western city tram project. The results show that the use of single line shallow foundation critical load would overestimate the allowable design value, resulting in a dangerous design.