Using the data from large-truck crashes in Los Angeles over an eight-year period (January 1, 2010 to December 31, 2017), the variation in the influence of factors affecting injury severities during different time periods of the day (morning and afternoon) and from year to year is studied. To capture potential unobserved heterogeneity, random parameters logit models with heterogeneity in the means and variances of the random parameters were estimated considering three possible crash injury-severity outcomes (no injury, minor injury, and severe injury). Likelihood ratio tests were conducted to assess the transferability of model estimation results from different times of the day and from year to year. Marginal effects of the explanatory variables were also calculated to investigate the stability of individual parameter estimates on injury-severity probabilities across time-of-day/time-period combinations. A wide range of parameters were considered including drivers’ characteristics, driver actions, truck’s characteristics, weather and environmental conditions, and roadway attributes. The results show instability in the effect of factors that influence injury severities in large-truck vehicle crashes across daily time periods and from year to year. However, there were several variables that exhibited relatively stable effects on injury-severity probabilities including driver ethnicity, crashes occurring while backing, sideswipe crashes, hit-object crashes, parked-vehicle crashes, fixed-object crashes, and truck-driver at fault crashes. The findings of this study should be useful for decision makers and trucking companies to better regulate truck operations by time of day.

使用八年期间（2010年1月1日至2017年12月31日）洛杉矶发生的大型卡车坠毁事件的数据，得出影响一天中不同时间段（早上和下午）受伤严重程度的因素影响的变化），并逐年进行研究。为了捕获潜在的未观察到的异质性，考虑了三种可能的碰撞伤害-严重性结果（无伤害，轻度伤害和重度伤害），估计了均值和方差均具有异质性的随机参数logit模型。进行了似然比测试，以评估模型估计结果在一天中的不同时间以及每年的不同年份之间的可传递性。还计算了解释变量的边际效应，以研究各个参数估计值在一天的时间/时间段组合中对伤害严重性概率的稳定性。考虑了广泛的参数，包括驾驶员的特征，驾驶员的行为，卡车的特征，天气和环境条件以及道路属性。结果表明，在每天的时间段和每年的时间里，影响大型卡车碰撞事故严重程度的因素的影响是不稳定的。但是，有几个变量对伤害严重性概率表现出相对稳定的影响，包括驾驶员种族，倒车时发生的撞车，侧滑撞车，撞到对象的撞车，停放的车辆撞车，固定的对象撞车以及卡车司机在故障撞车时。