“There is no such thing as free parking! Free parking represents lost revenue, squandered land and polluted air. Parking garages are not more than an antisocial car subsidy,” writes Donald Shoup in his book “The High Cost of Free Parking.”

Free and cheap parking is expensive for cities. It becomes a pull factor for commuters to bring their cars every day, together with the pollution they create, traffic congestion, accidents and lost revenue for public transport.

It is estimated that over 30% of traffic in a city is created by people looking for parking. If cities could reduce that number to about 10%, it could mean a significant reduction of overall traffic congestion and pollution.

This can be achieved not by increasing available parking space, but by regulating all possible curbside and public parking and adjusting price to demand. If the price of parking is high enough, there will be vacancies. Pricing should be adjusted to a point that there are always a couple of free slots per city block.

In New York, Jerome Barth, director of operations for the 34th Street Partnership, a business improvement group, said: ”This is one more way that New York is ahead of the country. In New York, you can park anywhere you want, if you can pay $30 an hour.”

In Barcelona about half of the 140,000 curbside parking spaces are regulated, leaving more that 70,000 free of charge. This is not only an invitation to use those spaces as long-term storage for rarely used cars, but an enormous loss of potential revenue for the city.

To make things worse, and visually ugly, it is legal for motorcycles to park on sidewalks, as long as they leave a 2.5 m (8ft 2.4in) clearance for pedestrians. Effectively, all motorcycles in Barcelona park for free, and there is little enforcement of the few rules that do exist, for instance leaving enough room for pedestrians.

If a city wants to reduce traffic and pollution, make parking more efficient, increase revenue and become more pedestrian friendly, it should implement a series of policies that could, in a short time, have a significant impact:

Eliminate non-regulated parking spaces in the city. Any “free” curbside parking is lost revenue, more pollution and an “invitation” to bring more cars into the city. Gradually expand parking for motorcycles to a third of the curbside space available, and eventually ban sidewalk parking for all motor vehicles. Have a “zero-tolerance” policy toward violations such as parking on pedestrian crossings, idling the engine while waiting, and any illegal parking on sidewalks. Don’t issue any new parking garage licenses and eliminate minimum parking requirements for new buildings. Adjust pricing to demand. If there is no curbside or public garage parking available it means the price is too low. Consider, as several cities have done, on-demand price adjustment. Enforce parking time limits. People should not be allowed to keep their cars parked in the same zone for more that the maximum time, even if they continue to pay. This will deter commuters from bringing their cars in each day. Eliminate “free” periods such as at lunch time, in the summer or on weekends. This would generate enough revenue to justify hiring additional meter maids. Gradually upgrade all the parking meters and ticketing machines to cashless units, requiring people to use electronic payment systems such as credit cards or smartphone apps. This way there is less maintenance, faster transactions and no cash collection costs. Finally, over time, automate the entire curbside parking system, installing sensors and electronic monitoring, and only bringing meter maids when necessary to issue a penalty. This way fewer meter maids could effectively handle bigger areas.

While some of these policies would likely ignite protests by residents and visitors alike, the results would bring many benefits that people would ultimately appreciate. A reduction in traffic and pollution could be achieved in as little as a few months, and people would be more accepting after experiencing the benefits.