Both ASB and ATLS are needed to control rail and road traffic at the South Main Street grade crossing
near one of the Norfolk Southern-CSX diamonds in Fostoria
The ASB (Active Signal Block) system is designed to prevent virtual collisions between trains on crossing mainlines. Fostoria, however presents a configuration beyond the design of ASB, in that there are three main line crossings in town which form a triangle.
In reality, the CSX "F" Tower, located at the B&O-C&O diamond, controls the traffic through town by radio. Engineers radio the tower in approach to Fostoria, and correspond similar to what is done with air traffic control. The objective in this Trainz version, is that portals will feed the Fostoria triangle from each direction with predesignated consists, and an automatic control system will prevent collisions in the triangle, thereby giving the "feel" of radio control tower management.
Fostorians are very patient people!
In practice, Fostoria trains often stop on the diamonds and grade crossings, and speeds can get rather slow, especially since two diamonds also serve to feed yards! It is not uncommon that a grade crossing on a fairly important street be obstructed with a train dead stopped, waiting for mainline or yard track clearance. Also trains "turning" between the C&O and B&O lines, which are about 30% to 40% of the CSX trains, are only moving at 15 to 20 mph, also delaying those gates from going up quickly.
Cam and Radio Observations of the actual triangle...
show that two trains are permitted in the triangle at once, but a third would be forbidden. To have that happen with an automatic control system, it would be necessary to have a "comparative" operator which processes signals from two different trigger channels. The outer triggers on the triangle would detect the approach of a train into the triangle, while an inner trigger set would confirm the presence of a second train in the triangle. If both inner and outer channels are tripped, the red signals would light up which prevent a third train from entering the triangle.
Unfortunately, there is no device in ASB which can compare and react to two incoming channels. Therefore, a simplification will need to be made to use the ASB system in Fostoria. The most apparent alternative is to combine the two closer intersections with the same ASB set up (that is two double mainline diamonds be treated as if four tracks crossed by two tracks). Any comments or thoughts on this problem are welcome.