🚀 Feature: Reduce Fidelity of the Roadway Network

[DavidOry]

User Story

The TM2 roadway network is very detailed. This results in very long runtimes. To reduce the runtime, we will remove the "local" roads (facility type 7) from the TAZ-scale roadway assignment. These roads will be retained in the MAZ-scale roadway assignment.

Progress:

• [x] Sufficiently defined
• [x] Approach determined
• [ ] Tests developed
• [x] User story satisfied
• [ ] Doc strings
• [ ] General documentation
• [ ] Passing tests

Priority

High

Level of Effort

About 80 hours

Resolution Ideas

1. In Lasso, remove the facility type 7 roads from the TAZ roadway network. When doing this, check for toll plazas that are coded with this facility type. Retain toll plazas. Also need to check if buses run on FT 7 roads. We need to retain links that buses traverse.
2. In Lasso, create a separate MAZ-scale roadway network. Retain all roads in the MAZ assignment.
3. In Lasso, rebuild the centroid connectors so that they connect to higher facility types
4. Do a roadway assignment. Measure the difference in runtime.
5. Create the Acceptance Criteria summaries. Compare the difference in validation performance (using the same demand).

Project

ActivitySim/Emme Conversion, Task Order 5

Who should be involved?

Users: @lmz Reviewers: @gregerhardt, @AshishKuls

Risk

Yes, there may be some zones that have very long centroid connectors, resulting in unattractive assignment outcomes.

Tests

• [ ] Runtime comparison for the full and reduced networks
• [ ] Acceptance Criteria validation comparisons for the full and reduced networks

[i-am-sijia]

Related issue: #115

[DavidOry]

A few notes:

1. Compare volumes before and after to see for outliers.
2. Examine high volume links before trimming to see if FT is wrong.
3. Reduce closing criteria so we can do an apples-to-apples assessment of reduced iterations.

[gregerhardt]

Fully support this task. Let's trim, and let's make some difference maps of assigned volumes in both just to make sure there is nothing weird that gets dropped and re-routed.

[DavidOry]

Results:

Run	Description	Assignment Iterations[EA,AM,MD,PM,NT]	TAZ Assign and Skim Run Time (hours)
3	assignable, relative_gap=0.05	3,10,9,19,4	5
8	drop FT7, relative_gap=0.05	3,21,19,51,4	7
11	keep FT7, relative_gap=0.05	3,15,14,32,4	11.5

The key takeaways are as follows:

• The assignable network drops links that are not used in an assignment. This is attractive as it leads to an attractive assignment, but unattractive in that it is likely hiding network errors and results in inconsistent network fidelity.
• Dropping the FT7 links results in a fairly sparse network. Though it has many fewer links than the assignable network, it takes more iterations to find a solution due to congestion on the smaller (FT 6) roads (which use the steep Akcelik curves).
• Removing the assignable and just using the FT7 links results in a much more detailed network. It requires fewer iterations to solve than the FT7 network, but each iteration takes much longer due to the detail in the network.

In sum, this avenue of exploration did not bear fruit. Additional, manual network coding would be required to find a simpler network that does not result in substantial congestion on lower facility roadways.

@lachlan-git: can you please add a table with the number of links for each of these runs?

[DavidOry]

Here's an image of the Sunset in SF with the FT 7 links in orange, which shows how sparse the network becomes when the links are removed.

[lachlan-git]

Hi, here are the link counts for runs 3, 8 and 11 broken down by ft.

@ft	3	8	11
1.0	3666	3666	3666
2.0	3485	3485	3485
3.0	6446	6447	6447
4.0	39050	39050	39050
5.0	58376	58254	58312
6.0	77878	95219	95457
7.0	171718	19828	405903
8.0	32982	34166	39862
99.0	29198	11729	12155
Total	422799	271844	664337

Edit: Note: run 3 ft8 only TAZ connectors are included individual counts are (MAZ 175936, TAP 36438, TAZ 32982,TANA 2998) In run 8-11 may differ more then expected due to dropping of isolated links when creating network.