Exploration of sample quantiles and mean speed distributions

In highway traffic analysis, speed and traffic flow are essential parameters. The 85^th and 15^th percentiles are commonly used. Comparative assessments of qualitative service often rely on descriptive statistics of speeds. In some studies, the focus has been on sampling distribution of the mean instead of the sampling distribution of the percentile while some have applied the binomial test for percentiles. This paper aims to explore two statistical tests on 85^th percentile speed using an impact study of rainfall carried out in Terengganu. Hypothesis was set up for performing simple percentile or quantile test and sample mean test. The normality of the data was evaluated and results show that speed reduction was statistically significant in all cases. The paper concluded statistical test for percentiles based on Crammer theory of asymptotic distribution of sample quantiles is a better fit when testing for statistical significance of speed changes occasioned by rainfall.