Abstract: Three main sources of random vibration test spectra for simulated road transportation tests are discussed in this paper, including the recommended test spectra in the international general standards, and in the Chinese national, military and aerospace standards. The Normal Tolerance Limitation method is used to establish the simulated road transportation test spectrum for the field test data, and with a basic procedure to build an envelope. A PSD envelope adjustment method is proposed for the multibody dynamic simulation according to the speed of the vehicle and the road grade. It is indicated that in conducting the simulated road transportation test, the test spectrum from the field test data should be used first, then the adjusted PSD envelope is chosen from similar products. If both these sources are not available, the test spectra from the relevant standards can be adopted.