I am posting this information here from the Train-Sim forums because this is a significant improvement for MSTS:

 

After beta testing by our Czech friends the version 1.6 of MSTbin is now downloadable from here:
http://mstsbin.uktrainsim.com/
Let me list only some of the highlights.
Standard MSTS bug removals:
- no more calls to Bill with front coupling
- possibility to browse throughout all a front coupled cars/carriages within F9 window without calls to Bill
- waiting points working and insertable in amount greater than 3.
Additional features:
- automatic night cab (if available)/day cab switching accordingly to time of day and tunnel/no tunnel
- switching from front cab to rear cab (if available) within same engine
- switching from cab of one engine to cab of any other engine within same player consist, even if other engine coupled after start of activity
- switching through all available passenger views within the player consist
- extended browsing with external cameras.

Valuable feature: new cabs added (night and rear) mantain trainsets runnable under standard MSTS (downward compatibility), but of course without their functionality

Also included are a sound patch (which corrects a lot of the problems with how MSTS deals with sounds, making some problems with soft horns and such go away) and the clear driving aids update (makes the aids transparent).

The update changes the way MSTS uses memory to call objects.  The biggest benefit people have found is that they can run routes which required them to reduce the sliders to prevent a crash at full value now.  I can personally say I have been able to run some of the more resource intensive routes (Cascades Crossing for example) without the annoying pauses where MSTS would have to load the next tile.  Even the pauses for an approaching train seems to be gone.  Lights are back on long trains, and the sound is unbelieveable now. 

The patch also allows you to change between cabs on locomotives attached to your train.  This lets you build a consist in the yard and attach the locomotives, then switch to the head end power, disconnect the switcher, and go.  You can also have reversed pairs which allows better helper activities (one cab for uphill, then disconnect, switch ends, and be able to see going back down). You can also disconnect a caboose with a passenger view, do your switching, then reconnect to the caboose and get the view back (it used to be gone).   

If you don't like it or it doesn't seem to work for you, it has an uninstaller to remove it.