And then there are the pre-empt signals, which permit trains to go through intersections where the trains and cars run in mixed traffic.
But since pre-empts on their own don’t tell you anything about how switches are set or train occupancy, when in pre-empt territory you need…
ABS/Pre-empt combination signals
Which I admit I have a tendency to short to “combination signals” and then even from that to “combo signals” because that’s altogether kind of a mouthful.
Combination signals can display both the red aspect of an ABS signal, indicating STOP as well as the yellow horizontal and white vertical aspects of a pre-empt signal. They are used in pre-empt territory for several reasons:
1. To switch a train to a secondary or tertiary route
2. To indicate occupancy of someone else in the circuit
3. To prevent a train from moving into a conflicting move
4. To keep trains from going on the Steel Bridge if/when a bridge lift is in progress
Diverging to another route
Remember how the number of aspects lit on an ABS signal tells you which route you’re going on? (one aspect = primary route; two aspects = secondary route; 3 aspects = tertiary route, etc). Well it’s the same with ABS/pre-empt combo signals. I’ll keep using W2 as an example. If it helps, here is the 11th Ave terminus from above. W2 is located on the corner of 11th and Morrison and is used by trains heading west.
For Blue (westbound to Hillsboro) and Red (westbound to Beaverton Transit Center) trains under normal operating conditions, W2 will pretty much behave as a regular pre-empt signal once the operator places their call for W2 at Galleria.
This indicates STOP and is what W2 looks like by default until an operator selects their route from the Galleria platform. Similar to a red on an ABS signal, reds on combination signals will be associated with ATS magnets that a train cannot move over.
When an operator of a Blue or Red line train is at Galleria, they watch W2 (which is a block away) and wait for the red to become this yellow horizontal. That shows that their switches are set to continue straight on to Hillsboro/Beaverton (primary route, so one aspect), and by the time they get up to the intersection of SW 11th & Morrison, it (should!) turn to this:
Which, as you already know, indicates “proceed with caution.” Because you get dumbass cyclists like that one biking against the light. Good job, unknown cyclist – lucky for you that train was going straight and not going to hit you as you cycled across the diverging tracks!
Here’s how the switches look to an operator – the train I was on when I took this photo was a Blue Line stopped at Morrison. This train would be continuing west instead of diverging into the terminus, and so the switches are set for the primary route, which is to head west towards Beaverton/Hillsboro. You can see the yellow horizontal on W2 in the top left corner of the picture, which indicates that the switches are set for the primary route but we can’t enter the intersection yet.
When Yellow Line trains used to turn around at 11th Ave, they’d get a different aspect after selecting their signal from Galleria:
The indication of this signal is “STOP – switches are set for something other than the primary route (more than one aspect), but you don’t have pre-emption to enter the intersection yet” – these aspects would display for trains diverging into the terminus after their switches were set and before the permissive white pre-empt aspect(s) came up.
So my picture of W2 showing a red over white diagonal over white vertical aspect indicates permission to proceed with caution on the tertiary route. 3 aspects = tertiary route. The tertiary route from W2 is the easternmost diverging track into the terminus.
A secondary route on W2 would be the red aspect over just a white vertical, but I never got a picture of that – if all tracks at 11th Ave were empty, a Yellow Line train would first be put in the tertiary track, and the secondary track would be used if another Yellow Line train entered the terminus while the first was still there. That didn’t happen while I was standing there taking pictures that day.
Other combination signals that will show these same indications for primary, secondary, and tertiary routes can be found at end of the line signals W1760 immediately prior to the terminus at Hatfield in Hillsboro, and M164 which is the combo signal immediately prior to the Jackson turnaround for Yellow/Green Line trains at PSU. There is also 18B into Rose Quarter from the east, which allows a train to continue on the normal westbound track (primary route), the special events track (secondary route), or the Vintage Trolley barn (tertiary route).
Sorry for the blur but it’s the only picture that I have of an ABS/pre-empt combination signal displaying a secondary route – Secondary route on W1760 (under the car traffic light, it’s a red over a white vertical)
On the other side of the 11th Ave terminus for eastbound trains is signal W6, another combo signal. An eastbound train coming up Yamhill can’t enter the terminus so W6 isn’t there for route selection, but a red on it will indicate that something else is in the circuit – either a train leaving the terminus, or a streetcar on 11th Avenue.
Red on W6 – because a train is leaving the terminus, so the ATS magnet associated with W6 will prevent an eastbound train from colliding with it
Permissive white vertical on W6 & eastbound train – you can see that the train that was pulling out of the terminus in the picture above this one is far enough ahead that it’s safe for this eastbound train to keep going.
Preventing a train from moving into another train’s conflicting move
There is a siding track that diverges off Holladay at 11th which used to be used by the Vintage Trolley and is occasionally used by MAX trains taken out of service (and yes, another combination signal – 20A – is used to make that diverging move). Signal 20C at Lloyd Center westbound is associated with that siding track.
A train facing this direction has no option to choose a different route, but the combo signal will prevent a westbound train from moving forward if a train is going to go into or come out of the Doubletree Siding.
Steel Bridge Lift
All signals leading to the Steel Bridge (on the east side of the river that’s the Rose Quarter platform for Blue, Red, and Green trains and Interstate Rose Quarter for Yellow trains; and on the west side of the river that’s the Oldtown/Chinatown platform for Blue and Red trains, and the intersection of NE 3rd & Glisan for Yellow and Green trains) are combos. Whenever the bridge is lifted, it throws up reds on all of those surrounding signals. As mentioned in the Automatic Train Stop post, although a yellow horizontal and a red both indicate STOP, a train still can physically move on a yellow horizontal, but it (by default) can’t move on a red. So as soon as the bridge span is unlocked for a lift, all trains will be prevented from getting anywhere near it.
The interlocking of tracks around the Steel Bridge is extremely complex – on the west side, the Yellow and Green Lines cross the Steel Bridge from a different angle than the Red and Blue Lines, and then on the east side the Yellow Line turns north towards Expo and the other lines continue east. Since all of those moves are done through switches in the rails, the combination signals will also display reds if another train is making a conflicting move (e.g. if a PSU-bound Yellow Line at Interstate Rose Quarter leaves the platform just before a westbound Red/Blue/Green line train tries to leave Rose Quarter), or if the switches aren’t set right for you – this is why sometimes you will be sitting on a Yellow or Green line train at 3rd & Glisan waiting to cross the bridge for a while (which means a Blue or Red left Oldtown/Chinatown and got onto the bridge before you got there), or similarly be sitting at Rose Quarter on a Blue, Red, or Green train waiting for a Yellow Line to get out of the way.
Both of those above ABS/pre-empt combination signals are capable of:
switching a train to another route (this is how trains can get from here over to the Expo Center from the Ruby Junction railyard – they can diverge from here)
preventing a train from moving if there is another train in the circuit
preventing a train from moving if the switches aren’t set right for them, and
stopping a train if the Steel Bridge is going to be lifted.
And that pretty much covers the last of the 3 major signal types used on the MAX light rail alignment.