The DTM GP50 and GP30 do not have scripted (CMP) brakes. The DTG scripted brakes took a round-about way to achieve a degree of realism and failed IMO. I'm not sure if there is a train simulator available to the public that fully mimics the modern Westinghouse air-brake. There are several that get darn close, but I haven't seen any that recreate air signal propagation. I'm having difficulty in explaining the process, so I'll refer you to Al Krug's explanation:
http://www.railway-technical.com/brake2.shtmlPropagation is the idea that each freight car can "help" the next realize an application or release is in progress. I wish I could explain this part better.
When freight cars sense a rise in air pressure during an air-brake release, they fully release rather than releasing at the rate of the brake pipe psi increase. All it takes is an increase of a few psi to cause a modern triple-valve to proceed with the release process. It does take time for the release signal to be sent to the end of a long train, so the release may seem somewhat slow.
Air pressure in a brake pipe can also mimic fluid dynamics. If I make a heavy set at the head end, air rushes forward from the end of the train to compensate for the lack of pressure at the head end. It then can "pile up" at the head end because of it's violent rush forward. Then, like a wave of water, the air pressure will head back to the rear, moving back and forth for a short period of time. In some cases, if you make a heavy set and close the trailing unit's angle ** before this sloshing back and forth stops, the sloshing can actually create enough of a psi change to tell the triple-valves that they should release where the air piles up. This is one reason why you should never "bottle" the air: closing the angle cocks on both ends of a consist to be dropped. A full release can be caused by the sloshing back and forth. Also, a triple-valve with an internal leak can feed air from it's reservoir back into the brake pipe, and can also raise the brake pipe's psi enough to trigger a full release.
Another interesting note: triple-valves react to the speed at which the brake pipe is vented as well. In any normal application, pressure is vented at a controlled pace and the triple-valve can sense this and trigger a normal application of the brakes on each car. However, if an emergency application is made, the pressure reduction is dramatically quicker. Triple-valves can sense the difference and trigger an emergency application rather than applying at the normal rate.
As an engineer, you watch the equalizing reservoir gauge to make an application. You decrease the equalizing reservoir to the pressure you want and the brake pipe pressure will follow and match it. Then watch the Air Flow Meter to determine when the "sloshing" has stopped. The AFM is also used during a release, as it can tell the engineer when the brake pipe is still charging even if the brake pipe gauge reads a full release pressure. The AFM will settle down when all of the train's auxiliary reservoirs have been recharged. Very few simulated locomotives include a working AFM.
Last fun fact for the night, as I'm tired and not really sure if I'm making any sense.
If you have a long train, let's say 120 cars, there will be small leaks throughout the train. A terminal air test should determine if these leaks are within an acceptable rate. A real mind-blower for me was learning that the EOT pressure at the rear of the train may never reach the full brake pipe pressure...ever. Your feed valve may be set for 90psi, but the rear of your train may only be able to reach 80psi. The fun thing is its all relative, and a 10 psi reduction on the head end will trigger a 10 psi reduction at the rear resulting in equal braking even though the actual numbers are different.
Ok, I'm done. If the PRR SD45 is ever released, I'll probably buy it.
Tyler