This paper shows that the heterogeneity of drivers’ and vehicles characteristics makes platoons, on average, more string-unstable. However, the string instability degree of unstable platoons is much higher in a homogeneous flow than in a heterogeneous one. These results are based on an ${\mathcal{L}}_{\infty }$ characterization of string stability, which is shown to be the most appropriate one from a traffic safety viewpoint. Mechanisms and conditions are discussed in which an ${\mathcal{L}}_2$ characterization is not able to capture the amplification of a speed drop through a string of vehicles. An analytical sufficient condition for the ${\mathcal{L}}_{\infty }$ string stability of heterogeneous vehicles, which move according to a general class of car-following models, is derived. Above all, a thorough comparison of ${\mathcal{L}}_{\infty }$ and ${\mathcal{L}}_2$ string stability characterizations between a homogeneous and a heterogenous flow, is performed. To this aim, the ${\mathcal{L}}_{\mathrm{p}}$ norms of heterogeneous platoons are calculated within a quasi-Monte Carlo framework. The variability of the ${\mathcal{L}}_{\mathrm{p}}$ norm values due to the platoon length, the equilibrium speed, and the probability distribution model of the uncertain vehicle parameters, is analysed. Overall, it is shown that the platoon stability behaviour sensibly changes with the shape and the correlation structure of vehicle model parameter distributions. Therefore, traffic heterogeneity needs to be modelled in order to correctly characterize the string stability of a mixed traffic flow.

本文显示，驾驶员和车辆特性的异质性使排平均更不稳定。但是，在非均质流中，不稳定排的弦不稳定度要比非均质流中的高。这些结果是基于${\mathcal{大号}}_{\infty }$字符串稳定性的表征，从交通安全的角度来看，这是最合适的一种。讨论了机制和条件，其中${\mathcal{大号}}_{\mathrm{2个}}$表征不能捕获通过一系列车辆的速度下降的放大。分析的充分条件${\mathcal{大号}}_{\infty }$推导了根据通用的汽车跟随模型类别移动的异构汽车的弦稳定性。最重要的是，对${\mathcal{大号}}_{\infty }$ 和 ${\mathcal{大号}}_{\mathrm{2个}}$进行均质流和非均质流之间的串稳定性表征。为此，${\mathcal{大号}}_{\mathrm{p}}$异类排的标准是在准蒙特卡洛框架内计算的。的可变性${\mathcal{大号}}_{\mathrm{p}}$分析了由于排长，平衡速度和不确定车辆参数的概率分布模型引起的标准值。总体而言，结果表明，随着车辆模型参数分布的形状和相关结构，排稳定性行为发生了明显的变化。因此，需要对流量异构性进行建模，以正确地表征混合流量的字符串稳定性。