Suggest a suitable analytical study design mentioning any desired assumptions, to achieve the following aims: a$)$ To study the effect of trauma on drivers involved in crashes in the past $3$ years and the time they take to resume driving. b$)$ To investigate the effect of a new proposed road sign at an intersection on the speed of drivers. c$)$ To examine the effect of age and gender on crash risk among drivers. Mention the following details of study: target study population, data required$-$ dependent variable and independent variables, how we analyse or interpret results or what do we compare the results to$,$ what kind of relationship between variables are you seeking, how do we ensure that there is no bias in the study population?