0 responses to “Portland Streetcar Loop Environmental Assessment Available”

1. Thanks for posting this info, Bob.

   Appendix D has some interesting design components, including some confusing ones. D-2, for example, shows the Lovejoy & Broadway signal at the west end off the Broadway Bridge. The streetcar makes turns crossing vehicle lanes, requiring pre-emption, but does so FROM vehicle lanes, which means that vehicles would potentially block the streetcar from being pre-empted. How will this work?

   Example: the eastbound streetcar turns left from the right lane of Lovejoy into the left lane of Broadway. It cannot theoretically do this with a vehicle green, as to do so would require the streetcar to make a dangerous lane change in traffic. But, it cannot be pre-empted either, because cars will theoretically be waiting in front of it at the light. Similar is true here for the westbound streetcar (right turn from the left vehicle lane).

   I wonder if there will be a new type of signal phasing? Or, is this design incorrect?

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2. Unit –

   That is a very good question about the lane switching and signal phasing … perhaps Chris knows who we should ask?

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3. I believe the intent is that Streetcar will have it’s own signal phase to make this movement (as we have done at other locations with similar challenges). That would mean the stop bar for the adjoining lane would need to be moved far enough back that there would not be other vehicles in the way.

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4. Here is the link to Appendix D-2 (pdf format) which Unit is referring to:
   http://www.metro-region.org/files/planning/020108pdxscloop_ea_j.pdf

   What is interesting here is that the same issue occurs in either direction.

   Westbound on the Broadway Bridge, there are two vehicle lanes which may continue southbound on Broadway. One of these vehicle lanes mixes autos and streetcars, but the streetcar needs to cross over the adjacent auto lane in order to turn onto Lovejoy, where it also merges with the westbound auto turn movement and shares a single westbound lane on Lovejoy.

   Eastbound on Lovejoy, there are two vehicle lanes which may turn eastbound onto the Broadway Bridge. In this case, the streetcar shares the right lane with autos but must cross over to the left lane as it crosses the bridge.

   Either of those movements creates a “lane change in an intersection” which can conflict with cars. In the case of westbound travel, a diverging parallel lane must be crossed and a further merging lane must be entered.

   I can envision this working only if each individual lane, even parallel lanes moving in the same direction (for autos) are independently signalled.

   For example, if a mixed auto/streetcar lane has an approaching streetcar, it (and only it) can go green to allow autos to clear out of the way and for the streetcar to pass, but neighboring lanes can’t go green until that streetcar is at the very least safely visible in the middle of the intersection.

   The signal phasing here really seems quite critical (and I’m assuming most of the issues here have something to do with the streetcar being structurally required to use the center lanes of the bridge, otherwise why the complication?)

   I really would like to know what the proposed signal solution is, and if a study has been completed yet which shows the vehicles per hour that can move through that intersection.

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5. Metro had a video simulation of how the Broadway/Lovejoy preemption works at one of the public meetings awhile back.

   With a green signal the streetcar pulls all the way forward to the stop line, then comes to a complete stop with no autos in front of it. Preemption then begins and traffic signals immediately cycle to red. With all traffic stopped and no autos in front blocking it, the streetcar can then make the turn across traffic (allowed by a special “train only” signal), and the traffic signal goes back to green, resuming the signal cycle where it left off.

   While this briefly interrupts the flow of auto traffic and requires the streetcar to make a complete stop, it is much safer than signaling each parallel lane independently. Oh, and the video was part of a traffic modeling program to see how it would impact traffic. I don’t recall the results, but I don’t think it was a significant impact.

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6. Chase B –

   Thank you for that explanation. That’s good information to know about the proposed signal cycles.

   If anyone from Metro is tuning in, perhaps we can work together to get this video posted online somewhere.

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