Parking garage exhaust calculation

So I'm designing an underground parking garage and I know that enclosed parking garages require an exhaust rate of 0.75 cfm/sq. ft. when CO or NO2 are activated. The minimum continuous exhaust shall be 0.05 CFM/sq. ft. and the total system shall be capable of 0.75 CFM/sq. ft. 

Mechanical ventilation systems for enclosed parking garages shall be permitted to operate intermittently in accordance to the Energy Code. Which are controlled by carbon monoxide detectors applied in conjunction with nitrogen dioxide. 

I've typically designed one continuous Exhaust Fan for the 0.05 cfm/sq. ft. and another fan for the 0.70 CFM/ sq. ft. 

Here is my question...isn't there an ASHRAE calculation where you get the total number of parking space, longest distance traveled from the farthest parking space and it outputs a value of CFM for exhaust. I recently changed jobs and I forget where this calculation came from. Thanks!

Found it... 2015 ASHRAE handbook HVAC applications. 15.18

https://www.portlandoregon.gov/bds/article/131139

I live in the City of Portland so it's a design alternative

Or you just simplify the system by only allowing electric cars...

Dexman PE PMP said:

Or you just simplify the system by only allowing electric cars...

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Or just put these at both entrance and exit:

Audi driver said:

Or just put these at both entrance and exit:

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I like these ideas!