People v. Banks (1993) 6 Cal.4th 926, which was decided after Ingersoll and Sitz, and incorporated a discussion of both cases in the opinion, the California State Supreme Court held that advance publicity is not an essential element of the constitutionally of a valid drunk driving roadblock. The Court concluded that although advance publicity remains a factor to consider, the lack of it alone does not render the roadblock unconstitutional. People v. Banks (1993) 6 Cal.4th 926. The following considerations expand upon the general headings listed above: Decision making must be at a supervisory level, rather than by officers in the field. A neutral formula must be used to select vehicles to be stopped, such as every vehicle or every third vehicle, rather than leaving it up to the officer in the field. Primary consideration must be given to public and officer safety. The site should be selected by policy-making officials, based upon areas having a high incidence of drunk driving. Limitations on when the checkpoint is to be conducted and for how long, bearing in mind both effectiveness and intrusiveness. Warning lights and signs should be clearly visible. Length of detention of motorists should be minimized. Advance publicity is necessary to reduce the intrusiveness of the checkpoint and increase its deterrent effect. Effectiveness There is a dearth of research regarding the deterrent effect of checkpoints. The only formally documented research regarding deterrence is a survey of Maryland's "Checkpoint Strikeforce" program. The survey found no deterrent effect: "To date, there is no evidence to indicate that this campaign, which involves a number of sobriety checkpoints and media activities to promote these efforts, has had any impact on public perceptions, driver behaviors, or alcohol-related motor vehicle crashes and injuries. This conclusion is drawn after examining statistics for alcohol-related crashes, police citations for impaired driving, and public perceptions of alcohol-impaired driving risk." Centers for Disease Control and Prevention, in a 2002 Traffic Injury Prevention report, found that in general, the number of alcohol-related crashes was reduced by 20% in states that implement sobriety checkpoints compared to those that do not. Public Health Law Research, an independent organization, reported in a 2009 evidence brief summarizing the research assessing the effect of a specific law or policy on public health, that there is strong evidence supporting the effectiveness of selective breath testing sobriety checkpoints as a public health intervention aimed at reducing the harms