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Most people's first thought is to use all the available trackage for the reverse section - probably because that's the way it's done with analog toggle switch block control.

And with block control, that's OK - simply because engineers are used to being cognizant of where block gaps are, and are always at the ready to flip a toggle or rotary switch. But, with DCC, not only is none of this necessary, long reverse sections can be detrimental and therefore unwanted.

First, keep in mind that other brands of reverse section controllers not only require the reverse section to be longer than the longest power pickup train, but also require that power pickup train to be fully out of the reverse section before the next train can enter at the other end.

Also keep in mind that DCC eliminates the need for engineers to be cognizant of blocks and limit lines, as it should. And with an automatic reverse section controller, engineers will not only forget where the gaps are, but actually forget that the reverse section even exists.

So, with other brands of reverse section controllers the reverse section must be kept long enough for the entire train of power-pickup cars (up to 20 or 25 feet), and engineers may forget that there is a reverse section. Any time a train is entering one end of the long reverse section at the same time a power pickup train is still exiting the other end, you will have a short circuit - the booster will shut down and won't fire up again until you clear the short manually.

But, with an ARSC, you can make the reverse section very short - it only needs to be as long as the longest MU lashup that goes through it.

For example, let's say that you run 5-unit diesel MU lashups. Even Dash-9s are only 10 inches long (HO-Scale), and it's a rare sight to see more than three of these lashed up. So, since four feet will easily accommodate any reasonable diesel lashup, four feet is as long as your reverse section needs to be, unless you have some unusual special need.

Even if you wanted to model the UP jockeying 10 locos back south from Los Angeles, it would only need to be seven or eight feet long.

Even if your reverse section has to be as long as eight feet, that's still a good bit shorter than 20' or 25'. But more important, with a Loy's ARSC, a loco can enter one end while a power-pickup car is exiting the other end - without any adverse affects. The only requirement is that a loco does not enter a portal at one end while another loco is within the portal at the other end.

How long does the reverse section "need" to be? With the ARSC, it must be long enough to contain the locos in an MU lashup, AND any cars that have all-wheel power pickup.

For example, the Roco DCC operational Crane has all-wheel power pickup, so it must be counted as a loco when considering the length of your reverse section. If you couple it up right after the last loco in the MU lashup, think of it as just another loco in lashup. But if you couple it six feet back in a cut of cars, you have to accommodate the fact that you'll have a loco entering the reverse section six feet back from the last loco. If your reverse section (including both portals) is shorter than six feet, there's no problem - the crane won't be entering the reverse section until after the locos have exited. As long as the crane isn't crossing one portal while the locos are crossing the other one, there's no problem.

Most lighted passenger cars, and other cars with power pickup, usually do not have all-wheel power pickup. Most of these cars pick up power from the right rail with the front truck and from the left rail with the rear truck. This is how the ARSC tells a power-pickup car (to ignore) from a loco (to switch polarity), and to provide other advantages over other reverse section controllers.

There are some cars that get power from both rails with both trucks (all-wheel power pickup). In this case the ARSC sees them as a locos and therefore has to either be treated like a loco (the reverse section being as long as the longest train with these cars), or disable some of the power pickup to make them look like a car.

Currently, the only cars I'm aware of that come with all-wheel power pickup from the factory are Kato N scale lighted passenger cars, the Roco DCC controlled crane car, and some Roco lighted passenger cars.

So, again, how long does the reverse section need to be? Easy - at least as long as the longest MU lashup that will go through it. It doesn't hurt to make it a little longer than anticipated - just in case you decide to occasionally run a longer than normal lashup through it.

Unless you have special needs, 3 feet is usually more than long enough for N-scale, 5 feet for HO-Scale, and so on.