Economics Today 18th Edition by Roger LeRoy Miller

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A Zero-Price Price Ceiling Comes to an End in Los Angeles
John Anthony DiCiaccio, an engineer with Southwest Airlines, returns to the space in the Los Angeles LAX Airport parking lot where he had parked his all-electric Toyota Prius. DiCiaccio is dismayed to find on the windshield a sheet announcing an end to free parking for electric vehicles for up to 30 days in parking lots containing battery charging stations.
LAX Airport is ending the zero-price policy because it has created a major parking-space shortage. This shortage has arisen for three key reasons. First, some people really do park their cars for as long as 30 days in the designated spaces, which are among the most conveniently located parking spaces at the airport. Doing so enables them to avoid paying up to $30 per day to park their vehicles elsewhere. While those vehicles sit in spaces for a month at a time, the spaces are unavailable to other drivers. Second, many people driving hybrid vehicles that also run on gasoline have sought to avoid paid parking by interpreting the zero-price-forelectric- cars policy as applying to hybrid cars as well. Third, more people actually have been buying electric vehicles.
Now so many people want to park their electric cars at a price of zero that traffic jams have developed in the zero-price lots as people driving electric and hybrid cars await open spaces. To bring an end to these mob scenes, the airport has decided to terminate this policy.
Why does a zero-price restriction for a scarce good necessarily lead to a shortage?