The purpose of shortlisting in the IBC, or the early stage of the SSBC, is to narrow down options on which detailed analysis and evaluation will be carried out, avoiding the need for such analysis of each and every option in a longlist.
As with many such questions, there is no hard-and-fast rule specifying how many options to take forward at the end of an IBC. However, there must be at least:
Often the best way forward won’t be clear even when the shortlisted options have been evaluated, in which case more than one shortlisted option should be taken forward for more detailed analysis.
It is also good practice to check in with decision makers at the end of shortlisting, since they may require that a particular option is developed further alongside the preferred option and do-minimum. For example, one of the options may deliver against wider organisational goals and objectives and an informed decision is needed as to whether this should be chosen ahead of the preferred option.
After alternative and option development, a simple intersection improvement might be found to only have limited options (for example, a do-minimum option comprising changes to markings/signage and sight lines; install a roundabout; install traffic signals; partial or full grade separation).
In situations like this, it may be possible to quickly develop a longlist, then workshop this with stakeholders to qualitatively evaluate options against investment objectives and identify a single preferred option at the IBC stage, without doing a lot of detailed analysis of each option.
Addressing traffic and pedestrian conflicts in a rural town might require more detail (including public consultation, consenting risk, geotech risk, etc) on a number of alternatives and options before a preferred option can be confirmed. For example, it may be hard to distinguish between options that improve the existing street environment against those that bypass the town, based purely on transport considerations.
In that case, the extra work to understand these details will almost certainly be beyond the scope of the IBC, as significant further work is likely to be required. Depending on circumstances, it may be possible to carry out the additional work through a cost-scope adjustment to the IBC, or it may be included in the first stages of the DBC (effectively taking two or three options forward for more detailed analysis).
For practical purposes, the important requirement is to make sure everyone is clear on why a particular approach is being adopted, and that there is a clear focus on understanding risks and using that to inform decisions.
Note: In both the examples above, a do-minimum option must still be taken through to the DBC, along with any preferred option(s), so that a comparison can be made.
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