From page 48 of "Track Buckling Prevention: Theory, Safety, Concepts, and Applications," Federal Railway Administration, March 2013:

Rail Neutral Temperature Frequency

CWR installation temperature is typically set within a desired range established in the railroad’s procedures and is typically between 90 °F and 110 °F, depending on the geographic location. This installation temperature is the rail initial neutral temperature. However, as research has shown [12, 14], the neutral temperature does not stay at the rail installation temperature and can decrease to lower values, as low as 50 °F in some cases. These reductions generally result from rail and track movements (creep, curve breathing, track settlement) and track maintenance activities.

The Rail Safety Advisory Committee on CWR Standards has adopted a "RNT reduction factor of 30 F" as the standard value to use when evaluating long-term RNT in the context of resistance to buckling (and the calculation of temperature limits for speed restrictions).

This webinar presents the case for an enhanced calculation of speed restriction temperature, using RNT, the RNT reduction factor, and an assumed buckling strength temperature increase based on track condition. Note that on page 5, there is a reference to a 'conventional' application of a speed restriction at temperatures from 10 to 20 degrees above initial RNT (as opposed to the more complicated formula described on page 8). This presentation takes some time to wade through and understand, but it is pretty interesting.

http://www.lbfoster-salientsystems.com/ ... -19-13.pdf" onclick="window.open(this.href);return false;

So, an initial RNT of 105 derates to 75. Assuming the track quality is strong (100 F factor) - especially after the current construction efforts - the enhanced formula in this presentation would produce a speed restriction temperature of 155 F (100-20+75). Note that is RAIL temperature, and the current industry standard is that rail temperature = ambient temp + 30 F. So a rail speed restriction temp of 155 = ambient temp of 125 F. If you assume only an 'average' track condition (80 F factor), then the ambient speed restriction factor drops to 105 F ambient. Fun with math to go from a RNT of 105 right back to an ambient speed restriction temp of 105. Funny how the formula works that way. It certainly supports the conjecture from "the EGE" that they are aiming for a high enough temperature that exceeds reasonable New England ambient temperatures.

I'm sure they are using some kind of formula to calculate RNT - everything I have seen indicates that the CWR-SAFE software is in widespread use. The contract documents for the project indicate a target RNT of 105.

I have no idea how the MBTA is applying these calculations and factors, but clearly a higher RNT results in a better safety factor for mitigating the potential for buckling.