Admittedly, parked cars do not cause emissions. At first glance, they also don't contribute to traffic jams, make any noise, or clog up inner-city streets. But there is also the other view: Even when stationary, cars consume quite a bit of urban space. As a rule, this area is sealed, not covered with vegetation. It therefore does not absorb surface water and does not contribute to a good microclimate. In addition, classic parking strips or parking bays along streets - typical on-street parking - often cause conflicts with other road users. Cars parked there obstruct the view of children and adult pedestrians, pose a danger to cyclists, and sometimes literally get in the way of contemporary bike lane planning.
In addition, the land consumption by off-street parking alone is presented as problematic by some stakeholders. The fact is, parking lots consume land - whether they are used or not. The Land Justice Report  of the Initiative for Smart Cities  uses the example of Berlin to show that 39 percent of all traffic areas in the city are earmarked for moving cars, and another 19 percent for parked cars. This means that stationary cars alone take up six times as much of Berlin's traffic space as moving bicycles. And the consulting firm Deloitte has calculated for twelve major German cities that the 4.3 million cars registered there add up to a total area of around 34 square kilometers. That is an average of 7.2 percent of a city's total area. 
Before cars reach their "resting place," however, they first have to head for it. However, it is seldom possible to find a free parking space in the desired vicinity of the destination. Consequently, conventional parking initially causes parking search traffic. The U.S. economist and urban planner Donald Shoup and his research colleague R. C. Hampshire looked at Stuttgart's city center against this background. According to this study, no less than 15 percent of all car traffic there is accounted for by the search for a parking space. APCOA, a parking space management company operating throughout Europe, also found in a study that the search for a parking space accounts for a considerable proportion of traffic in conurbations. According to this study, the search for a parking space in Germany takes an average of ten minutes. In the process, an additional 4.5 kilometers are traveled - and each search pollutes the environment with 1.3 kilograms of CO2 emissions.
Not only do these emissions and land consumption put question marks behind the sustainability of conventional parking, but it can also affect the individual well-being of those looking for a parking space. Transportation service provider Inrix has taken a close look at the time lost, costs and psychological impact of searching for a parking space. According to the study, two out of three drivers feel stressed by searching for a parking space, and one in five has had an argument with another motorist over a parking space. 44 percent missed an appointment because of the search for a parking space, 27 percent gave up an outing because no parking space could be found. More than half of those surveyed believe there is too little parking space in Germany. Added to this is the massive loss of time: in the ten largest cities in Germany, motorists spend an average of 41 hours a year looking for a parking space.
Is parking a car alone a contribution to climate and traffic gridlock? Certainly not! On the contrary, there are numerous concepts and practical examples of how parking areas for cars can become a mobility hub. If motorists can reach their destination from there on foot, by public transport, with emission-free micromobility, with sharing vehicles and the like, then off-street parking areas become an important component of sustainable mobility. Then they will relieve roads, residents and other road users of traffic and emissions. Then these mobility hubs will enliven city centers with people instead of cars. Then they will promote urbanity.
One thing is certain: parking is and will remain a mainstay of individual mobility. People will only go where a vehicle is parked reliably and legally. For far too long, however, this insight has been implemented by creating more and more parking spaces - often so many that they are not used to their full capacity. Which in turn means unnecessary, unsustainable land consumption.
So how can we reconcile the two: the justified need for parking space as a prerequisite for individual mobility and the equally justified demand to further develop transportation systems in terms of environmental compatibility?
A key approach is to make more efficient use of the limited space available in large cities. This means making better use of parking spaces and efficiently distributing the available spaces to as many parkers as possible.
The key to this is digital development of parking areas. Digitalization is changing parking and parking behavior. Above all, however, it creates new opportunities to no longer view parking as a stand-alone function, but to integrate it into the ecosystem and mobility mix of a city. The central prerequisite for opening up a parking area digitally is camera-based license plate recognition and, if necessary, a digital payment system. The primary goal is to provide a convenient user experience with entry and exit without tickets or automatic pay stations.
parkoneer transfers this idea from public spaces to private parking areas: Businesses, residential complexes, retail, leisure venues, and buildings with a mix of such uses often have parking areas that are only occupied at certain times and by certain target groups. But why should a supermarket parking lot sit empty overnight while concertgoers cruise through the neighborhood next door looking for parking? Why shouldn't residents' parking spaces be used by shoppers or day-trippers during the day? Why shouldn't the colleague at work park her car in the reserved company parking lot of her colleague at the home office?
Sharing existing spaces and thus making better use of them not only fits in with the contemporary idea of the share economy and makes people individually happier - it also offers tangible benefits in many dimensions of sustainability.
First of all, digitally managed parking space does not cause any parking search traffic, because motorists head directly for their online-booked parking space. This significantly reduces traffic volumes as well as noise and pollutant emissions, as the above figures show. And, of course, the otherwise so frequent annoyance about the difficult or even unsuccessful search for a parking space is eliminated.
In addition, there is another effect that should not be neglected: more efficient use of existing space eliminates the need for many a new building, which would otherwise inevitably have environmental and climate disadvantages. This approach is also sustainable because it enables many a company to grow organically at its existing location - because the availability of parking space for the workforce grows along with it as a result of dynamization.
Space is a scarce and valuable commodity in the vast majority of cities. It should not be wasted. Empty parking spaces, however, ARE a waste. No one would think of building an office building if it were clear from the outset that it would be only 50 percent occupied on average. Of course, this can happen in practice, but it should never be the basis of planning.
Efficiently utilized parking spaces pay off on another dimension of sustainability: Getting more and more cars off the parking strip and onto digitally managed parking spaces opens up new scope for planning bike paths or other urban infrastructure.
Fewer emissions, less consumption of resources and space, less time wasted, fewer relocations, and more satisfied people. This balance shows: Intelligently managed parking is not part of the problem, but becomes part of the solution.
 Robert Cornelius Hampshire and Donald Shoup: What Share of Traffic is Cruising for Parking? Journal of Transport Economics and Policy 52, 2018
 APCOA PARKING Study quoted in: https://www.trendreport.de/die-evolution-des-parkraums/
 https://inrix.com/press-releases/parking-pain-de/, Munich 2017