Mapping Center Answer:

This railroad symbol can be recreated as a representation rule with a stroke layer and a marker layer. Use the following settings:

Stroke layer (line):

Apply the Dashes Geometric effect to the stroke layer and define the settings (all units in millimeters):

     Pattern (pattern, gap): 4.5 .75
     Endings: No constraint
     Width: 0.125 mm
     Caps: Butt
     Joins: Round

Marker layer:

The first step is to create a new marker in the Marker Editor window:

1. Use the Create Line tool to create a line.
2. Copy and paste this line.
3. Orient the lines parallel to one another; they should be offset from one another but centered horizontally about the x in the middle of the Marker Editor window.
4. Click OK.

The new marker should look something like this:

Set the size of the new marker symbol and then apply the Dashes Geometric Effect.  The settings should be:

     Pattern: 0 0.375 0.8 7.39 0.8 1.125
     Endings: No Constraint
     Size: 1.25
     Step: 10.115

You can then use control points to fine tune the behavior of the symbol around curves and corners. Your final result will look something like the image below:

For more information about working with control points, refer to ArcGIS Desktop Help 9.3.