This study investigates the lateral stability of A-double vehicle combinations,
focusing on the rearward amplification effect—a critical phenomenon where
dynamic responses amplify toward the rear units in multi-trailer configurations.
Utilizing TruckSim simulation, a validated multi-body dynamics model of an
A-double combination (a vehicle combination consisting of a tractor, a dolly,
and two semitrailers) was established. Based on different semitrailer lengths,
four configurations were analyzed using the model: 20 ft + 20 ft, 20 ft + 40 ft,
40 ft + 20 ft, and 40 ft + 40 ft. Simulations under a single sine-wave steering
input assessed key stability metrics, including lateral acceleration, yaw rate,
and their corresponding rear amplification factors (RAay and
RAr). The results confirmed the presence of motion lag and
rearward amplification (RA > 1) across all configurations. Stability was
found to degrade with increasing speed, as both motion responses and RA factors
increased. Among the configurations, the 40 + 40 combination demonstrated the
best stability (lowest RA factors and highest critical speed), followed by 20 +
40, 40 + 20, and finally 20 + 20. The study also revealed that stability
decreases when the payload center is positioned further from the hitch point or
at a greater height. These simulation findings were substantiated by
real-vehicle slalom tests conducted at the automobile test site, where the 20 +
40 configuration exhibited the best handling performance. The research concludes
that, for a given total mass, A-double combinations with longer semi-trailer
wheelbases offer superior stability, providing essential insights for optimizing
configuration design and promoting the safe application of high-capacity
vehicles in China.