I've just finished a very VERY preliminary review of the FRA's final PTC rule, and I think that while an MTEA (main track exclusion addendum) may be possible for NICTD (exempting the street running from the PTC mandate), it will be very difficult to obtain.
To be granted an MTEA, a passenger railroad can apply to have some of its trackage classified as "not main line" (and therefore be exempted from the PTC mandate), under the following conditions:
1. Tracks are used exclusively as yard or terminal tracks (the street running could possibly fit this bill, although it does not currently - the yard limits territory would need to be extended all the way through the street-running portion of the line),
2. Maximum authorized speed is 20 mph or less, and that speed is enforced by the PTC on-board system (current maximum speed is 25 mph; this would have to be reduced to 20 mph - not a tragedy, but also not something that NICTD will find very attractive, as it's a step backward in terms of the strategic vision of reducing travel times across the line),
3. Interlocking rules are in effect that prohibit reverse movements other than on signal indications without dispatcher permission (under NICTD's rules, this is the case or could be made the case), and
4. Either no freight movements are made (which is obviously an impossibility - the SouthShore Freight operates out of the Shops at Carroll Avenue and uses the street running territory to get to the west) - OR - Freight operations are permitted, but there will be no passengers aboard passenger trains within the defined limits (another impossibility, for obvious reasons).
So, under those guidelines an MTEA cannot be approved, mainly because of provision 4.
There are a second set of conditions under which an MTEA could be approved:
1. All trains are limited to restricted speed (which is 20 mph - current maximum speed is 25 mph, which would have to be lowered, as in the previous set of conditions; not attractive to the railroad),
2. Temporal separation of trains is maintained (freight and passenger trains do not operate on any shared segment of track during the same time period; I need to dig into this a bit more, since this is on its face impossible unless you prohibit SouthShore Freight to operate during times when NICTD does not - not going to happen) - OR - Passenger service is operated under a risk mitigation plan submitted by all railroads operating in the territory - NICTD and SouthShore Freight - and approved by the FRA.
An MTEA under the second set of conditions might be possible, but the key is the risk mitigation plan, which must under the final PTC rule "...be supported by a risk assessment establishing that the proposed mitigations will achieve a level of safety not less than the level of safety that would obtain if the operations were conducted under paragraph ©(1) or ©(2) of this section...", which means that NICTD and SouthShore Freight would have to absolutely convince the FRA that the street running operation is at least as safe as temporally separating the types of trains (i.e. having the freights operate at different time periods than the passenger trains). That might be a very hard sell.
So, this will be a challenge, to say the least.