What must be done regarding numbers or locations on a Form D when separated in a series?

The correct approach when dealing with numbers or locations on a Form D that are presented in a series is to use commas to separate them. This method ensures clarity and prevents any confusion that may arise when listing multiple entities. By using commas, each location or number is distinctly identified, making it easier for the dispatcher and train crews to interpret the information accurately and quickly.

In contrast, using periods could create confusion as they typically indicate the end of a sentence or thought, and inappropriate spacing might not convey the required separation. The option suggesting no special formatting would lead to ambiguity, potentially compromising safety and operational efficiency in communication. Therefore, the use of commas is essential in maintaining clear and effective documentation on the Form D.