Critical Path (CP) Drag shows amount of time that could potentially be saved on the project by reducing the duration of the activity or removing an activity completely.

However, CP Drag only identifies good candidates for optimisation. It doesn’t mean that such optimisation is possible. Two more criteria have to be met as well:

• Assignment of additional resources allows completing the activity in a shorter period
• Resources have to be available

Any activity has a maximum limit of resources that could be assigned to deliver the activity. The limit is due to technological processes (2 cars can’t deliver twice quicker than one car), space (no space for three cranes) or increasing complexity associated with required collaboration (no more than two designers per design).
There is a few ways for changes in resource assignments that can decrease activity duration:

• Additional resources (two extra workers)
• Increase % of assigned resources (80% -> 100%)
• Replace resources with a better productivity rate (10m/h -> 15m/h)
• Combination of the above changes

If there is an opportunity to speed up delivery by changing resource assignment, practically it is only possible when required resources are available when they are needed.

If additional resources are not available internally, it could be an opportunity to hire them. It usually means additional cost. In another hand, the project is likely to have direct and indirect benefits associated with reduced project duration. It includes:

– Reduced project management costs;
– Financial and reputational bonuses;
– Opportunity to reallocate resources to another project earlier.

Apart from Critical Path Drag, Stephen A. Devax introduced the Drag Cost metric that identifies if acceleration is beneficial. 

• The technological resource limit is a characteristic of activity. It has to be documented, and Resources Critical Path algorithms must consider resoucre possible limits.
• It may be possible to achieve the required result by applying different technological processes (workers with spades instead of bulldozer). In this case, the activity could be replaced with a different activity of a set of activities. 
• When CP Drag is negative, project acceleration could be achieved by increasing the number of assigned resources (anti-crashing method). However, activities also have lower limits: minimum required quantity (one worker to move a chair and minimum of two workers to move a desk) or minimum percentage of availability (assign resource with availability over 20% only). The lower limits must also be documented and used when calculating the resource-critical path.
• Other CP metrics are complementary to CP Drag: Start & Finish Flex, Super Float, and Activity Spread.
• Apart from crashing the acceleration could be achieved by changing schedule logic (fast-tracking)