Check for directional links with same from-to node pair

[nmpeterson]

It is currently possible to add two links to the MHN that connect the same two nodes. For this to happen, either the BASELINK values or the digitized direction (and therefore the ANODE and BNODE values) must differ. If at least one of the links represents a two-way road, the Emme batchin files may contain two links with the same inode and jnode, and only one of them will be imported. (The other will be ignored with a non-fatal warning.)

The MHN processing scripts should check for this possibility and warn the user. This could be done in one of two places:

1. When running "Incorporate Edits", check the DIRECTIONS values on any links sharing the same nodes to predict whether this issue may occur later; or,
2. When running "Generate Highway Files", check for duplicate inode-jnode pairs during the creation of the Emme batchin files.

I am not sure yet which approach would be best.

[nmpeterson]

While this issue is mostly fixed, there is still some nuance that could cause problems:

• If a skeleton link has DIRECTIONS='1' but has highway project coding applied to it that converts it to a bidirectional link, then the BNODE-to-ANODE direction could still result in an unidentified duplicate. The best way to address this would be to inspect the final directional links generated by the Generate Highway Files tool for each scenario and time of day period.
• Two directional links that are currently reported as duplicates might not actually be duplicates if their AMPM values don't overlap. For example, if two links with the same ANODE/BNODE pair existed, but one had AMPM1='2' (a.m. periods only) and the other had AMPM1='3' (p.m. periods only), the files created by Generate Highway Files would not actually contain duplicates, but these links would still trigger an error when running Incorporate Edits. Highway project coding can complicate this even further, so again, checking the directional links actually generated by Generate Highway Files might be the best solution.