The emergence of Intelligent Transportation Systems has given new hope and an unprecedented number of promising benefits to the transportation industry. However, these benefits are accompanied with inherent challenges due to the higher mobility of the vehicular nodes. One of the major problems faced is the induced Doppler shift in the carrier frequency of the transceiver node. This paper attempts to decrypt the effect of the Doppler shift impact in a Vehicle-to-Vehicle or Vehicle-to-Infrastructure communication system. Mobile nodes that are moving at a relative speed of 25 to 250 km/h are considered. Using a variable Modulation Code Scheme, the degradation effect in term of Bit Error Rate is analyzed under variable signal strength condition. Using the principle of Monte-Carlo, intense simulations are carried with a 95% Confidence Interval. Using the approximation technique, the results obtained from simulations prompted the derivation of a mathematical model. Considering the Bit Error Rate threshold limit defined by the standard, multiple simulation results are optimized to derive the composite result called the Doppler shift signature. A complete mathematical model of the Doppler shift signature accounting for all channel realizations when the Improved Direct Derivation Method is used in a Vehicular Ad-hoc Network is derived and compared against the actual. To assess and explore the effectiveness of the proposed model, several tests are conducted to evaluate the performance of the signature model against other existing rate adaptations, such as Adaptive Modulation Code, Binary phase-shift keying, and Constant. The results from simulation tests demonstrate that the proposed model in conjunction with the Improved Direct Derivation Method offers more than 200% improved throughput compared to its peers Adaptive Modulation Code, Binary phase-shift keying, and Constant.