A little message from Paul__B came in via PM. Don't know why Paul has the bad habit of answering by PM so here is the message (but I'm to lazy to add the quotes back in...). Also, Paul is now enjoying a place on my ignore list and all his PM's to me will be automatically be deleted. 
Paul__B:
Ah! Now that is the critical question! 
Because ...
That thing is, this is talking about model railway points. The solenoids require a current pulse of between two (Peco) and three (Hornby) Amps to operate. The TPIC6B595 might be useful to drive the 12 V High-side drivers, but nothing else. You would need some serious FETs to do the actual switching and in case the software glitches, it would be best to use a capacitor discharge system in any case.
And yes, it makes much more sense to use a six by six array, not just in terms of cost of components, but practicality of wiring and assembly. There is an excellent argument for using ready-made relay modules (eBay) instead of MOSFETs. In either case, you only need one diode for each switching device, not per solenoid. As I am fond of saying, "lead dress" of the entire layout is absolutely critical if you propose to use a microcontroller.
(And in fact the answer to that critical question was "four to six Ohms".
)
Alright, in my head a TPIC6B595 could switch more so yeah, it might be a little bit underrated. But 2A is already a lot for most turnout drivers! Drivers from Roco and Fleischmann will stay under that with ease. And luckely, you only need to give a pulse
But yeah, I would search for others. I like to use the IRF7313. Cheap, can switch a decent current and two in a single package but it's SMD.
And you don't save that much with 6x6 which uses 18 transistors where 2x17 just uses 3 transistors more. And the wiring is a heck more clear I would say. Just two common straight/diverging wires for the whole layout and a single wire per turnout. And very easy to expand.
And relays, possible. But it's more clunky and noisy. On the other hand, you would only need a single DTSP relay for it with 2x17.
And how would the single diode work?