Chapter 1. Introduction

Cruising vehicles cause a host of problems, such as adding congestion and air pollution to already congested and polluted neighborhoods, driver frustration, and a potential loss of economic competitiveness at destinations where parking is hard to find and where alternative access modes are limited. With increased sensitivity to the need for curb management, many approaches to understanding curb use and the prevalence of cruising for parking have emerged.

Strategies to quantify cruising have evolved from intercept surveys to sophisticated wireless technology sensors. Intercept surveys are effective at understanding the proportion of traffic that is looking for parking (which may not imply excess travel).⁵ Wireless technology deployment has been successful in distinguishing vehicles within the traffic stream that are circling for parking in very limited geographies.⁶

The extent of cruising remains unclear. Research has been conducted in the locations where cruising is known to be an issue. However, results have been inappropriately extrapolated across wide regions. For example, it is often taken on faith that “…30% of urban traffic comes from cars hunting for parking spaces.”⁷ This has been traced to an analysis⁸ that averaged the results of a limited number of studies and concluded that 30 percent of vehicles in congested downtowns are searching for parking. The misinterpretation stems not only from the fact that the studies were performed just where cruising was perceived to be a problem, but also from taking the straight average of these limited number of studies without regard to community size, date of the analysis, whether the analysis was conducted in a downtown or neighborhood, or other conditions that might affect the outcome. There have been attempts to debunk the 30-percent figure,^{9, 10} but it is still widely used in academic and policy settings.

Many existing research methods, such as counting vehicles passing an empty space and tracking parking availability by bicycle, quantify the percentage of traffic searching for parking, rather than quantify the excess traffic and pollution from cruising. The difference is subtle but important for policy; the strategy is also applicable only in limited geographies. Almost all trips end in a search for parking, with the exception of drop-offs and those ending in reserved parking. When close to a destination, up to 100 percent of traffic is searching for parking. A study that finds a high percentage of traffic is searching for parking may reflect the absence of through traffic as much as scarcity of parking. As shown in Figure 1, in some circumstances scarce parking could even reduce vehicle miles traveled. This occurs when drivers park short of a destination because they perceive parking to be scarce at the destination (not to mention when, for the same reason, they choose to forgo driving and instead access the destination using transit or non-motorized modes).¹¹

Source: FHWA.

Figure 1. Illustration. Scarce parking can reduce vehicle miles traveled.

This report extends previous work that had relied on global positioning system (GPS) breadcrumb data to overcome the physical limitations of other research methods. Big data allows for a more comprehensive assessment of the extent and location of excess parking search.^{12, 13} The method also quantifies the measure of most direct policy interest—excess travel from cruising, rather than the proportion of drivers searching for parking.

Along with documentation of the research strategy and Cruise Detector (i.e., the tool the study team developed to generate reliable estimates of cruising), this report includes case analyses from four U.S. cities. The cases illustrate a range of applications, such as identifying cruising hot spots by both time of day and location and assessing policy impacts. To assist cities in making parking policy and investment decisions, Cruise Detector is freely available and can be openly accessed.

Purpose and Scope

There are uncertainties and a lack of understanding of the full impact that parking cruising has on cities. There is also a paucity of understanding about the effectiveness of interventions. Recently funded studies include the direct precursor to this one,¹⁴ which provided a proof-of-concept to use GPS traces to identify a signature of cruising for parking. A related project¹⁵ deployed a set of wireless sensors throughout a study area that connects to devices in passing vehicles and identifies how often a vehicle passes the same point. Using information on how frequently and in what time frame a vehicle passes a certain point, an assessment is made regarding the extent of cruising in that area.

The National Cooperative Highway Research Program has undertaken a recent review of dynamic curb management.¹⁶ Any number of departments of transportation have looked into the question as well, with many adopting performance pricing (designed to align parking demand with parking availability) and other strategies to combat problems that stem from parking shortages. The scope and purpose of this work is to develop a robust, freely available tool (i.e., Cruise Detector) that allows cities to understand the impact and extent of traffic generated by parking search and to test policy interventions. This report provides documentation on Cruise Detector and discusses its application.

Cruise Detector can address the following questions (for the first four questions, specific examples of the analysis are provided in Chapter 3 of this report):

• How big a problem is cruising? The question is addressed using Atlanta, Georgia, as a use case.
  • How much cruising is there in specific urban locations?
  • How does cruising vary across space and time of day?
• Does cruising change from year to year?
  • An analysis of Chicago cruising in 2019 and 2020 is used as a month-over-month use case for the longitudinal analysis. The Atlanta case is also used to examine longitudinal differences examining travel and parking behavior in the months leading to March 2020 when pandemic lockdowns began and then for several months after.
• Where do people cruise? Washington, DC, serves as a use case to illustrate how a city might address these questions.
  • Is cruising more prevalent at tourism destinations?
  • In denser neighborhoods?
  • Around particular land uses?
• Are policies such as performance pricing effective in deterring cruising? Seattle, Washington, serves as a use case to determine this by answering these questions:
  • How effective are different management strategies in reducing cruising?
  • What happens when meter prices are adjusted to better match parking demand with supply?
  • What about meter suspension?
• Why do people cruise? No specific use case is presented for this question (although this study provides some insights related to the second question below), but it is an obvious question for Cruise Detector to address.
  • Do people cruise: 1) because no space is available, 2) because no space is available that is free of cost, 3) because no unrestricted (e.g., overnight allowed) space is available, or 4) because of other reasons?
• How do people cruise?
  • What are the patterns of a cruising driver?
  • Do these cruising behaviors cluster into types?¹⁷
  • Given types of cruising behaviors, what policy interventions will reduce cruising?
• What are the long- and short-term impacts of cruising on congestion?
  • How do they affect mode choice or car ownership decisions? For example, does reducing cruising promote mode shift to the private car, as finding parking becomes less onerous?