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Towards a behavioural approach to city centre parking
T!Wpatt Towards a behavioural approach to city centre parking The case of Jerusalem's CBD Ilan Salomon Department of Geography, The Hebrew University of Jerusalem, Israel
An understanding of the demand for city centre parking is an important input to policy making. This study emphasizes the importance and benefits of analysing the demand for parking at the level of individual users rather than basing analyses on traffic and parking counts . A survey of drivers' parking behaviour in Jerusalem's business centre was used . A structure is presented for analysing the driver's parking decision process and policy implications that can be drawn from disaggregate data are suggested .
Funding for this research was granted by the Charles H . Revson Foundation, through the Jerusalem Institute for Israel Studies . 'K, Orski,
'Suburban mobility : the coming transportation crisis', Transportation Quarterly, Vol 39, No 2, 1985, pp 283-296 .
200
Parking problems experienced by drivers are in fact a manifestation of the gap between supply and demand for parking space . While these problems are most obvious in city centres, they have become increasingly common in suburban areas .' A long held solution to the problem has been the construction of additional parking facilities to accommodate increasing demand . However, this solution entails high social costs : it requires massive
capital investments for acquiring land, for construction and, as supply increases, demand increases follow, with the associated congestion, pollution, energy and safety side effects . On the other hand, the parking problem itself, if left unsolved, also has negative consequences : streets congested by vehicles searching for parking or parked illegally, time wastage and unpleasant environmental effects . In the long run, transport and parking problems are caused by an exile of activities from the Central Business District (CBD) in favour of suburban centres, and in metropolitan areas this may mean a loss in the tax base for the central city . These parking related effects usually have political implications for elected officials, and hence often draw their attention . In view of the wide range of complex effects associated with the parking problem, planners, first in Europe and then in the USA, became aware of the fact that parking is no longer a pure transportation engineering problem but can in fact serve
0264-27511861030200-09$03 .00 ,c) 1986
Butterworth & Co (Publishers) Lid
Tiansspne as an important policy tool to shape urban activities . What is needed is a policy which can fine-tune the supply of parking so as to respond to a desired pattern of usage . For example, a parking space in the CBD can be occupied by a commuter's vehicle for eight hours a day or, alternatively, the same space can he used by eight shoppers' vehicles for one hour each . The latter can stimulate retail activity in the centre if that is a desired policy objective . This implies, first, that the number of parking spaces is an inappropriate measure of supply and should be substituted by the availability of parking hours . Second, it implies that policy instruments included in the Transportation Systems Management (TSM) approach, employed today by most Western world planning agencies, can be used to improve the efficient use of available infrastructure through low-cost management techniques . The use of such techniques in relation to parking and urban goals is reviewed by McShane and Meyer .'In order to devise parking policies it is necessary to identify the characteristics of parking demand .' While, conventionally, demand for a product or a service is defined in terms of a ratio between desired quantity and price, the demand for parking must account for certain attributes in addition to duration and price, such as time of day and location . Two basic approaches can be employed to estimate that demand . One common approach is to identify relationships between the numbers of cars parked, parking rates, and vehicle turnover rates in parking spaces . The major advantage of this approach is its relatively low cost . Yet, it treats the automobile as the basic unit of analysis, while the driver's decisions on parking are the relevant determinants of demand . Information collected on the driver or the trip, using this approach, is minimal, eg returnable postcards used by Hill' included only information on trip purpose, walking distance, trip origin, arrival time, departure time, trip frequency and comments .
CITIES August 1986
The objective of this paper is to demonstrate the benefits of using a behavioural approach in order to develop relevant parking policies, coherent with broader urban goals . The structure and analysis of parking behaviour. To accomplish the objective of this study, it is necessary to evaluate the benefits accrued by using disaggregate, user-level data to explain the demand for parking in a city centre . It is assumed that two types of drivers' decisions are of relevance, and should be
'a car owner faces a decision on whether to travel to the CBD by car' treated separately for purposes of policy formulation . First, a car owner faces a decision on whether to travel to the CBD by car. If the purpose of the CBD-bound trip is work, then the only alternative to the car trip, in the short run, is to travel by public transport .' In the long run it is also possible to relocate one's workplace or residence . For non-work trips, people may face a decision to travel by public transport, instead of using a car, thereby avoiding parking costs, or people may travel by car to a non-CBD location . The demand for parking is therefore influenced by the decision on whether or not a car trip to the CBD is made, and a different parking duration is associated with different trip purposes . The second relevant decision pertains to the driver who has decided to use a car on the CBD-bound trip and needs to decide where to park . This decision is dependent on the willingness to pay the expected parking rates, the attitudes towards walking or the ability to walk from the parking space to the final destination, the time constraints and the familiarity with the street and parking system . Obviously, it also depends on the supply of parking places . The decision on parking has a number of dimensions of interest to policy mak-
2M .
McShane and M . Meyer, 'Parking policy and urban goals : linking strategy to needs', Transportation, Vol 11, 1982, pp 131-152 . 3C . Ligocki and L. Zonn,
'Parking problems in Central Business Districts', Cities, Vol 1, No 4, May 1984, pp 350-355 .
'Downtown parking study : a different perspective', 4T . Hill,
Urban Analysis, Vol 7, 1982, pp 35-44 5The use of nonmotorized modes of
transport, which must not be overlooked, is a viable alternative, but only to a small market segment. 201
Taaspatt "M . Ben-Akiva and S . Lerman, Discrete Choice Analysis, MIT Press, Cambridge, MA, 1985 . 'C. Manski . 'Structural models for discrete data : the analysis of discrete choice', in S, Leinhardt, Sociological Methodology, Jossey Bass . San Francisco, CA, 1981, pp 58-109 . 8T . Adler and M . BenAkiva, Joint choice model for frequency destination and mode for shopping trips', Transportation Research Record, Vol
569, 1976, pp 136-150, I . Salomon and M . BenAkiva, 'The use of the life-style concept in travel demand models . Environment and Planning A, Vol 15,
1983 .pp623-638 :L . Silman, Disaggregate
ers . The driver faces a choice of parking facilities . Usually, the choice includes at least two alternatives : on-street and car parks, where the latter may he public (municipal) or private . These parking services vary in price, convenience, safety, security and expected availability of space . A distinction should also he made between legal and illegal parking options . For each parking type there are also alternative locations from which the driver needs to choose and this choice situation is depicted in Figure 1 . (Only locations within the CBD area arc referred to here . Park-and-Ride facilities are an alternative option in the previous decision .) The decisions on car usage in CBDbound trips can be formalized into discrete choice models which make it possible to estimate the probability of a driver making a particular choice, as a function
of a series of explanatory variables which describe the choice alternatives and the characteristics of the driver . Such models can be used for policy analysis, examining, for example, the impact of the variations in the parking rate structure on the choice probabilities . The coefficient of the utility function can be estimated based on sample data which include the actual decision made .. the characteristics of the alternatives in terms of level-of-set vice and characteristics of the decision makers . These models have been described in greater detail by Ben-Akiva and Lerman, 6 and Manski . 7 While such models have often been applied to the first type of decision . that of mode choice in the case of work trips or of a simultaneous choice of mode and destination in the case of non-work trips .' they have not dealt explicitly with parking . One reason is that to some extent the
Travel Demand Models for Short-term Forecasting, The Israel
Institute for Transportation Planning and Research, Tel-Aviv . Israel, 1980 .
particular site
remote parking
repeat search
Figure 1 . The choice of parking type .
202
CITIES August 1986
effects of parking policies can be simulated and measured by the existing specification . For example, changes in parking costs can be represented through a change in the out-of-pocket costs variable usually included in such models . However, a plausible argument may be made that parking search time differs in its effect on drivers' choice behaviour for both in-vehicle travel time and out-ofvehicle travel time and should therefore be treated separately . The second decision, that of parking type, has drawn less attention than the former choice of mode of transport . Ven der Goot y developed a logit type choice model in which he estimated the probability of choosing a given type of parking based on a set of variables describing the parking level-ofservice, ie walking distance from destination, rate charged, legality, occupation and accessibility . Separate models were estimated for different trip purposes . Two major drawbacks are evident in this model . First, it ignores the contribution of the decision maker's individual characteristics to the choice of parking type . Second, as noted by Van der Coot, the instantaneous supply or occupancy rate is probably an important explanatory v ariable . as elaborated below . Consider the choice process illustrated in Figure 1 . It is plausible to assume that at the outset (point A in Figure 1) a driver chooses between two alternatives : parking at a particular facility (eg a particular car park), or parking at an occasional spot which he or she will encounter on route to the city centre . The choice between these alternatives is actually a choice between parking at a facility where there is a higher level of certainty with regard to costs (both monetary and walking distance) and parking at an occasional spot which entails greater uncertainty with regard to these factors . Although the driver does not have perfect information on availability of space at the particular facility, he or she may have made a fair assessment, based on experience, of the expected space availability and cost .
CITIES August 1986
A driver on route to a particular site may find an occasional site which is preferred to that initially chosen . In this case (point B in Figure 1) he or she may choose to select the occasional site . The choice between the alternatives is therefore dependent upon the driver's characteristics (eg value of time, income, ability to walk), the expected availability of spaces in each alternative as perceived by the driver, and the level of service offered by each alternative . Simultaneous to the choice described in Figure 1 is an additional decision which may only he made by those drivers who do not consider parking at a particular facility . This decision is whether or not illegal parking will be considered as an alternative . A positive decision will increase the number of spaces available, as well as proximity to the destination . However, depending on the level of enforcement of parking regulations . the expected costs may be significantly higher than legal parking . A complication in analysing parking choice behaviour arises from the dynamics of the process . While the choice made by the driver at the beginning of the trip can he modelled as described above, there is only a limited certainty that his or her behaviour will in fact resemble the choice . The main reason is that the choice was made under uncertainty with regard to the actual, instantaneous supply of parking . Stated differently, as the driver approaches the city centre, he or she is gaining information on current supply which may alter the previous choice, and result in parking at a different site than initially intended . Observing actual parking level of service, that is, available spaces for given rates and distances from the final destinations, the driver may trade off attributes of level of service for uncertainty . An analysis of this process is too complicated at this stage, but the decision points C through F in Figure 1 represent the search behaviour through which a driver passes, making repetitive choices as vacant sites are observed .
9D . Van der Goot,'A model to describe the choice of parking places', Transportation Research A, Vol 16A, No 2, 1982, pp 109116 .
203
Taaspolt r-
'Ibid. "I . Salomon . Parking Habits in Jerusalem's Business Center, Report No 14, The
Jerusalem Institute for Israel Studies, Jerusalem, (Hebrew) . 204
The geography of the decision process shown in Figure 1 deserves attention as it may have some policy implications . Assuming that a driver chooses the shortest route to the CBD destination, and that a decision to park at an occasional space is made, there is a certain point along this route at which the search process begins . The exact point will vary between drivers, depending on their willingness to walk and their perceived probability of finding a space closer to their destination . This point may well be outside the city centre, causing a spillover of parking to adjacent neighbourhoods . A driver who chooses to begin the search closer to the CBD or not to park at the first available site, assuming a better one will be found, is in fact continuing a search with a decreasing probability of finding a parking space, if it is assumed that spaces are filled from the centre outwards . This may result in increasing the distance from the destination as parking close to the centre may be all occupied . In this case the driver may find an available site which is as remote from the destination as those available while approaching the CBD, except that higher costs, both financial and social, have been involved in the search . Some drivers may still decide to take the risk of spending additional resources in the search so as to increase their probability of finding a space close to their destination . In this case they will turn around and approach the CBD again . These drivers can be characterized as risk prone and having low values of time, and they cause superfluous traffic in the CBD . In summary, parking policy analysis can he performed by using discrete choice models which explain the decision to use a car for a trip to the CBD and the choice of specific parking types or locations . The second type of choice has not been developed here beyond the basic choice modelled by Van der Goot . 10 The Jerusalem parking study . In 1984 this author performed a study of parking in Jerusalem's CBD in which the emphasis
was on analysing drivers' behaviour rather than on counts of cars and parking spaces ." While for reasons described below, it was not possible to estimate the models described previously, the results arc indicative of the importance of employing a behavioural approach for devising relevant parking policies . Data for the study were collected from a number of sources . The municipal parking unit provided information on all parking sites and usage patterns in the study area, as shown in Figure 2 . The study area of 1 .25 km' was delineated, based on assumed regions which serve CBD-bound drivers as parking locations . Second, information on vehicle turnover in parking spaces was collected in an innovative manner . Rather than iterative registration of vehicles in parking spaces and an estimation of duration patterns based on the report of a periodic patrol, photographs of parking facilities and streets were taken periodically from the tops of high-rise buildings (Figure 3) . In this way, two people were able to cover a greater number of parking spaces than a conventional patrol and an additional advantage was that raw data were available for reference . Using photographs, vehicle identification is positive and the time required seems competitive with the conventional approach . The third source of data on parking users was a selfadministered mail-back questionnaire . It consisted of four parts : • • • •
information on the last CBD-bound trip, by any mode ; information on parking in the last CBD-hound car trip ; socioeconomic and demographic data ; respondents' comments on parking in the centre of Jerusalem .
The questionnaire was distributed to a random sample of Jerusalem's car owners . Of 2600 questionnaires sent out, only 25% were returned . In addition, 940 questionnaires were handed to drivers entering their vehicles in the CBD parkCITIES August 1986
riaasril
Figure 2 . Jerusalem - study area . ing facilities . Of these, 22% responded . A total of 849 valid questionnaires were available . The major problem encountered in this survey is that, not only was the response rate low, the respondents represented a very biased sample of the population, which prohibited use of the sample for model estimation . The mean level of education, for example, was 15 years which is likely to be significantly higher than the mean of all car owners in Jerusalem . Moreover, it is plausible to assume that drivers who encounter greater problems in parking are more likely to respond to the questionnaire, and thus may present extreme information . However, the data are useful in demonstrating the importance of behavioural
CITIES August 1986
approaches in parking studies, as shown below . The analysis of the data presented below provided information on the patterns of CBD-bound trips in Jerusalem . parking at the trip-ends and, more relevant to the current context, some insight into the contribution of behavioural approaches to policy-oriented parking studies . Jerusalem's CBD is still a major attraction for trips, despite growing competition from suburban shopping centres . Much of the retail activity in the CBD is chained to other CBD-hound trips . Of shopping trips, 37% also included destinations for personal business (eg bank, hairdresser, lawyer etc) . About 12% of 205
Taaspalt
Figure 3 . Street parking in Jerusalem .
the work trips, which constituted 40%, of all ('1313-bound trips, included shopping as a secondary activity . Further suburbanization of workplaces may thus have a negative effect on CBD retail activity and the vitality of the city centre . Despite the general perception of a severe parking problem at the centre, the predominant mode of travel to the CBD by car owners is by the car (90%) . Only W X, reported using taxis and no bus trips were reported, despite the availability of a frequent and inexpensive service to the centre from many outlying districts . 'I his indicates that the current costs of driving
'space available for shoppers is reduced by commuters parking in the city centre' 'Paid in Israeli Shekels .
206
and parking, including the time loss associated with congested streets and the search for parking, are not strong deterrants to driving to the CBD . Improvements in public t ransportation . as observed in many Western countries, arc probably insufficient as an incentive to
encourage the use of high-occupancy vehicles, and disincentives to car usage are necessary if an observable change is desired . The recent introduction of more stringent enforcement of traffic regulations may help in this respect . Long-term parking (longer than four hours) occupies at least 12 %, of the available spaces . Consequently, space available for shoppers is reduced by commuters parking their cars in the city centre . That may not be to the benefit of the commuters who may have an interest in the viability of the city centre, but fail to identify the relationship between their parking and the activity level of the CBD . Such long-term parking is encouraged by the prevailing pricing structure . Payments for parking are of two types : municipal car parks and street parking require the use of parking cards which costs $0 .22 (US dollars) 12 and $0 .11 per hour, respectively . Parking is legally restricted to two hours, but riot strictly enforced, as the use of multiple one-hour cards is tolerated . Private car parks charge an average of $0 .65 per hour and CITIES August 1986
r usually lower rates for additional hours . If encouraging short-term parking is a desired policy goal then intervention is necessary, by both a change in the pricing schedules and enforcement . However . intervention in the pricing schedule of private car parks is legally complicated . The search for parking, according to the (biased) sample, is relatively long . Between 8 .00 am and early afternoon the median is over 9 minutes, although for most of the day (except between 8 :00 am and 09 :00 am) the mode is zero . One possible technique to reduce search time is the use of dynamic signalling which would divert drivers from searching in areas which are fully occupied . Parking location was found to be related to the direction of access to the CBD . Drivers are more likely to park on the side of the centre from which they approach the CBD . This seems to be encouraged by the traffic management system which directs the flow so as to avoid traffic crossing the centre . The potential contribution of a behavioural approach could ideally be demonstrated by the development of models which show the relationship between revealed behaviour and characteristics of the decision makers and the alternatives they face . However, due to the bias in the sample, the value of a behavioural approach can only he shown indirectly . To this end, the analysis was performed separately for various market segments . The identification of different behavioural patterns across market segments serves two purposes : such differences support the hypothesis that there is a correlation between the decision maker's individual characteristics and parking behaviour ; and second, it may make it possible to devise parking policies to apply to certain market segments . A number of market segments, that is groups within the sample who demonstrate similarities in behaviour, have been identified . First, a distinction can be made between people who work at the CBD and those working elsewhere . The former usually enter the CBD earlier in
CITIES August 1986
f
the day and occupy parking spaces for longer durations than the latter . Second, differences in behaviour associated with gender and education levels were observed . Women who work in the CBD were found to park for shorter durations than men, possibly because many of them work part-time . However, there is no difference in parking duration between males and females among non-CBD workers, Women's search for parking was shorter by about 20%, than that of men for both CBD and non-CBD employees as can he seen in Table 1 . A possible explanation is that women tend to search in areas or car parks which have lower probabilities of occupancy . In addition, women reported higher rates of delinquent parking (not using parking cards) than men, a fact that may provide additional explanation for their shorter search . While it is not suggested that
`parking is viewed as a "free public good" ' policies oriented towards, gender-based market segments he employed, their clear difference in behaviour demonstrates the relevance of demographic and socioeconomic factors in understanding parking behaviour . The perceived risk of enforcement of parking regulations seems to he generally low and hence more than 50% of the drivers have admitted at the time the questionnaire was collected that they do not use the cards where required . This has probably changed recently as wheel clamps have been introduced . Differences in behaviour were identified among people with varying levels of education (elementary, high school and university) . Search time was negatively correlated with education level . A possible explanation is that people of higher educational level have higher values of time and plan their schedules so as to avoid long searches . This explanation is supported by the fact that the difference 207
Tianspnlt Table 1 . Parking search time by workplace and sex (minutes). Working in Number of cases Mean Standard deviation Median Mode % zero search time
"T.
Schelling,
Micromolives and
Norton, New York . 1978 . 1O G . Miller and C . Everett, 'Raising commuter parking prices -an empirical study', Transportation, Macrobehavior,
Vol 11, 1982, pp 105129 .
208
CBD
Working outside Male Female
Male
Female
320 10 .5
106 8 4
168 11 4
86 8 .7
107 96 0 .0
9 .9 5 .0 0 .0
11 .0 9 .7 0 .0
8 .8 5 .3 0 .0
24 .1
27.4
19 .9
24 .4
CBD
is consistent, even when parkers who have zero search time, presumably parking in car parks with higher rates, are eliminated . Another important finding of this study relates to drivers' perception of the 'parking problem' . Drivers fail to identify the social costs of providing parking in terms of the consequential traffic congestion, air pollution, safety and energy consumption . Moreover, the costs of land and construction are not appreciated . Parking is viewed as a `free public good' which drivers believe should be supplied by the authorities . Hence, the solution suggested by the respondents most frequently relates to the construction of more facilities and the reduction of rates . None have admitted to recognizing the relationship between increases in parking supply and street congestion . Only a few respondents suggested measures which would curtail trips by car to the CBD . Parking problems are not detached from the political policy-making process and often they rank high in the agenda of urban politicians, precisely because they are considered important by drivers . Yet, rather than accepting public criticism, the fact that drivers do not recognize the real social costs of supplying parking in city centres should be given further attention . Although, due to the fact that there is a gap between micro-motives and macrobehaviour," a better understanding of
the costs may not have a profound effect on drivers' behaviour, it can at least be used by elected officials to divert pressuree from drivers' interest groups . This is particularly true for commuters who have business interests in the CBD and who should become aware of the conflict between their use of parking and the revenues losses caused by parking shortages for shoppers . The policy implication is that more efforts must be directed at estimating and publicizing the high social costs of car usage and parking in the CBD . Conclusions . Three types of conclusions can he drawn from this study . First, while the reasons for the differences between market segments are not all clear and may be the subject of separate research, the identification of market segments by socioeconomic and demographic attributes supports the hypothesis that a disaggregate approach is beneficial for purposes of policy formulation, as each segment is expected to react differently to policy measures . Experience in raising parking prices in Washington . DC, for example, has demonstrated the different reactions to policy measures . t4 While the segmentation chosen in the Jerusalem study may only be illustrative, the conclusion with regard to the importance of using a behavioural approach is still valid . Second, specific policy implications can be drawn, even if formal models are not estimated, but merely on the basis of the user level data . Third, methodological lessons are learned from this study with regard to data collection . Specifically, the innovative photographic method of identifying vehicle turnover rates seems to be more efficient than the conventional approaches . Yet, the collection of disaggregate user data by means of a selfadministered questionnaire is problemmatic when the expected response is likely to overrepresent certain interest groups .
CITIES August 1986
An understanding of the demand for city centre parking is an important input to policy making. This study emphasizes the importance and benefits of analysing the demand for parking at the level of individual users rather than basing analyses on traffic and parking counts . A survey of drivers' parking behaviour in Jerusalem's business centre was used . A structure is presented for analysing the driver's parking decision process and policy implications that can be drawn from disaggregate data are suggested .
Funding for this research was granted by the Charles H . Revson Foundation, through the Jerusalem Institute for Israel Studies . 'K, Orski,
'Suburban mobility : the coming transportation crisis', Transportation Quarterly, Vol 39, No 2, 1985, pp 283-296 .
200
Parking problems experienced by drivers are in fact a manifestation of the gap between supply and demand for parking space . While these problems are most obvious in city centres, they have become increasingly common in suburban areas .' A long held solution to the problem has been the construction of additional parking facilities to accommodate increasing demand . However, this solution entails high social costs : it requires massive
capital investments for acquiring land, for construction and, as supply increases, demand increases follow, with the associated congestion, pollution, energy and safety side effects . On the other hand, the parking problem itself, if left unsolved, also has negative consequences : streets congested by vehicles searching for parking or parked illegally, time wastage and unpleasant environmental effects . In the long run, transport and parking problems are caused by an exile of activities from the Central Business District (CBD) in favour of suburban centres, and in metropolitan areas this may mean a loss in the tax base for the central city . These parking related effects usually have political implications for elected officials, and hence often draw their attention . In view of the wide range of complex effects associated with the parking problem, planners, first in Europe and then in the USA, became aware of the fact that parking is no longer a pure transportation engineering problem but can in fact serve
0264-27511861030200-09$03 .00 ,c) 1986
Butterworth & Co (Publishers) Lid
Tiansspne as an important policy tool to shape urban activities . What is needed is a policy which can fine-tune the supply of parking so as to respond to a desired pattern of usage . For example, a parking space in the CBD can be occupied by a commuter's vehicle for eight hours a day or, alternatively, the same space can he used by eight shoppers' vehicles for one hour each . The latter can stimulate retail activity in the centre if that is a desired policy objective . This implies, first, that the number of parking spaces is an inappropriate measure of supply and should be substituted by the availability of parking hours . Second, it implies that policy instruments included in the Transportation Systems Management (TSM) approach, employed today by most Western world planning agencies, can be used to improve the efficient use of available infrastructure through low-cost management techniques . The use of such techniques in relation to parking and urban goals is reviewed by McShane and Meyer .'In order to devise parking policies it is necessary to identify the characteristics of parking demand .' While, conventionally, demand for a product or a service is defined in terms of a ratio between desired quantity and price, the demand for parking must account for certain attributes in addition to duration and price, such as time of day and location . Two basic approaches can be employed to estimate that demand . One common approach is to identify relationships between the numbers of cars parked, parking rates, and vehicle turnover rates in parking spaces . The major advantage of this approach is its relatively low cost . Yet, it treats the automobile as the basic unit of analysis, while the driver's decisions on parking are the relevant determinants of demand . Information collected on the driver or the trip, using this approach, is minimal, eg returnable postcards used by Hill' included only information on trip purpose, walking distance, trip origin, arrival time, departure time, trip frequency and comments .
CITIES August 1986
The objective of this paper is to demonstrate the benefits of using a behavioural approach in order to develop relevant parking policies, coherent with broader urban goals . The structure and analysis of parking behaviour. To accomplish the objective of this study, it is necessary to evaluate the benefits accrued by using disaggregate, user-level data to explain the demand for parking in a city centre . It is assumed that two types of drivers' decisions are of relevance, and should be
'a car owner faces a decision on whether to travel to the CBD by car' treated separately for purposes of policy formulation . First, a car owner faces a decision on whether to travel to the CBD by car. If the purpose of the CBD-bound trip is work, then the only alternative to the car trip, in the short run, is to travel by public transport .' In the long run it is also possible to relocate one's workplace or residence . For non-work trips, people may face a decision to travel by public transport, instead of using a car, thereby avoiding parking costs, or people may travel by car to a non-CBD location . The demand for parking is therefore influenced by the decision on whether or not a car trip to the CBD is made, and a different parking duration is associated with different trip purposes . The second relevant decision pertains to the driver who has decided to use a car on the CBD-bound trip and needs to decide where to park . This decision is dependent on the willingness to pay the expected parking rates, the attitudes towards walking or the ability to walk from the parking space to the final destination, the time constraints and the familiarity with the street and parking system . Obviously, it also depends on the supply of parking places . The decision on parking has a number of dimensions of interest to policy mak-
2M .
McShane and M . Meyer, 'Parking policy and urban goals : linking strategy to needs', Transportation, Vol 11, 1982, pp 131-152 . 3C . Ligocki and L. Zonn,
'Parking problems in Central Business Districts', Cities, Vol 1, No 4, May 1984, pp 350-355 .
'Downtown parking study : a different perspective', 4T . Hill,
Urban Analysis, Vol 7, 1982, pp 35-44 5The use of nonmotorized modes of
transport, which must not be overlooked, is a viable alternative, but only to a small market segment. 201
Taaspatt "M . Ben-Akiva and S . Lerman, Discrete Choice Analysis, MIT Press, Cambridge, MA, 1985 . 'C. Manski . 'Structural models for discrete data : the analysis of discrete choice', in S, Leinhardt, Sociological Methodology, Jossey Bass . San Francisco, CA, 1981, pp 58-109 . 8T . Adler and M . BenAkiva, Joint choice model for frequency destination and mode for shopping trips', Transportation Research Record, Vol
569, 1976, pp 136-150, I . Salomon and M . BenAkiva, 'The use of the life-style concept in travel demand models . Environment and Planning A, Vol 15,
1983 .pp623-638 :L . Silman, Disaggregate
ers . The driver faces a choice of parking facilities . Usually, the choice includes at least two alternatives : on-street and car parks, where the latter may he public (municipal) or private . These parking services vary in price, convenience, safety, security and expected availability of space . A distinction should also he made between legal and illegal parking options . For each parking type there are also alternative locations from which the driver needs to choose and this choice situation is depicted in Figure 1 . (Only locations within the CBD area arc referred to here . Park-and-Ride facilities are an alternative option in the previous decision .) The decisions on car usage in CBDbound trips can be formalized into discrete choice models which make it possible to estimate the probability of a driver making a particular choice, as a function
of a series of explanatory variables which describe the choice alternatives and the characteristics of the driver . Such models can be used for policy analysis, examining, for example, the impact of the variations in the parking rate structure on the choice probabilities . The coefficient of the utility function can be estimated based on sample data which include the actual decision made .. the characteristics of the alternatives in terms of level-of-set vice and characteristics of the decision makers . These models have been described in greater detail by Ben-Akiva and Lerman, 6 and Manski . 7 While such models have often been applied to the first type of decision . that of mode choice in the case of work trips or of a simultaneous choice of mode and destination in the case of non-work trips .' they have not dealt explicitly with parking . One reason is that to some extent the
Travel Demand Models for Short-term Forecasting, The Israel
Institute for Transportation Planning and Research, Tel-Aviv . Israel, 1980 .
particular site
remote parking
repeat search
Figure 1 . The choice of parking type .
202
CITIES August 1986
effects of parking policies can be simulated and measured by the existing specification . For example, changes in parking costs can be represented through a change in the out-of-pocket costs variable usually included in such models . However, a plausible argument may be made that parking search time differs in its effect on drivers' choice behaviour for both in-vehicle travel time and out-ofvehicle travel time and should therefore be treated separately . The second decision, that of parking type, has drawn less attention than the former choice of mode of transport . Ven der Goot y developed a logit type choice model in which he estimated the probability of choosing a given type of parking based on a set of variables describing the parking level-ofservice, ie walking distance from destination, rate charged, legality, occupation and accessibility . Separate models were estimated for different trip purposes . Two major drawbacks are evident in this model . First, it ignores the contribution of the decision maker's individual characteristics to the choice of parking type . Second, as noted by Van der Coot, the instantaneous supply or occupancy rate is probably an important explanatory v ariable . as elaborated below . Consider the choice process illustrated in Figure 1 . It is plausible to assume that at the outset (point A in Figure 1) a driver chooses between two alternatives : parking at a particular facility (eg a particular car park), or parking at an occasional spot which he or she will encounter on route to the city centre . The choice between these alternatives is actually a choice between parking at a facility where there is a higher level of certainty with regard to costs (both monetary and walking distance) and parking at an occasional spot which entails greater uncertainty with regard to these factors . Although the driver does not have perfect information on availability of space at the particular facility, he or she may have made a fair assessment, based on experience, of the expected space availability and cost .
CITIES August 1986
A driver on route to a particular site may find an occasional site which is preferred to that initially chosen . In this case (point B in Figure 1) he or she may choose to select the occasional site . The choice between the alternatives is therefore dependent upon the driver's characteristics (eg value of time, income, ability to walk), the expected availability of spaces in each alternative as perceived by the driver, and the level of service offered by each alternative . Simultaneous to the choice described in Figure 1 is an additional decision which may only he made by those drivers who do not consider parking at a particular facility . This decision is whether or not illegal parking will be considered as an alternative . A positive decision will increase the number of spaces available, as well as proximity to the destination . However, depending on the level of enforcement of parking regulations . the expected costs may be significantly higher than legal parking . A complication in analysing parking choice behaviour arises from the dynamics of the process . While the choice made by the driver at the beginning of the trip can he modelled as described above, there is only a limited certainty that his or her behaviour will in fact resemble the choice . The main reason is that the choice was made under uncertainty with regard to the actual, instantaneous supply of parking . Stated differently, as the driver approaches the city centre, he or she is gaining information on current supply which may alter the previous choice, and result in parking at a different site than initially intended . Observing actual parking level of service, that is, available spaces for given rates and distances from the final destinations, the driver may trade off attributes of level of service for uncertainty . An analysis of this process is too complicated at this stage, but the decision points C through F in Figure 1 represent the search behaviour through which a driver passes, making repetitive choices as vacant sites are observed .
9D . Van der Goot,'A model to describe the choice of parking places', Transportation Research A, Vol 16A, No 2, 1982, pp 109116 .
203
Taaspolt r-
'Ibid. "I . Salomon . Parking Habits in Jerusalem's Business Center, Report No 14, The
Jerusalem Institute for Israel Studies, Jerusalem, (Hebrew) . 204
The geography of the decision process shown in Figure 1 deserves attention as it may have some policy implications . Assuming that a driver chooses the shortest route to the CBD destination, and that a decision to park at an occasional space is made, there is a certain point along this route at which the search process begins . The exact point will vary between drivers, depending on their willingness to walk and their perceived probability of finding a space closer to their destination . This point may well be outside the city centre, causing a spillover of parking to adjacent neighbourhoods . A driver who chooses to begin the search closer to the CBD or not to park at the first available site, assuming a better one will be found, is in fact continuing a search with a decreasing probability of finding a parking space, if it is assumed that spaces are filled from the centre outwards . This may result in increasing the distance from the destination as parking close to the centre may be all occupied . In this case the driver may find an available site which is as remote from the destination as those available while approaching the CBD, except that higher costs, both financial and social, have been involved in the search . Some drivers may still decide to take the risk of spending additional resources in the search so as to increase their probability of finding a space close to their destination . In this case they will turn around and approach the CBD again . These drivers can be characterized as risk prone and having low values of time, and they cause superfluous traffic in the CBD . In summary, parking policy analysis can he performed by using discrete choice models which explain the decision to use a car for a trip to the CBD and the choice of specific parking types or locations . The second type of choice has not been developed here beyond the basic choice modelled by Van der Goot . 10 The Jerusalem parking study . In 1984 this author performed a study of parking in Jerusalem's CBD in which the emphasis
was on analysing drivers' behaviour rather than on counts of cars and parking spaces ." While for reasons described below, it was not possible to estimate the models described previously, the results arc indicative of the importance of employing a behavioural approach for devising relevant parking policies . Data for the study were collected from a number of sources . The municipal parking unit provided information on all parking sites and usage patterns in the study area, as shown in Figure 2 . The study area of 1 .25 km' was delineated, based on assumed regions which serve CBD-bound drivers as parking locations . Second, information on vehicle turnover in parking spaces was collected in an innovative manner . Rather than iterative registration of vehicles in parking spaces and an estimation of duration patterns based on the report of a periodic patrol, photographs of parking facilities and streets were taken periodically from the tops of high-rise buildings (Figure 3) . In this way, two people were able to cover a greater number of parking spaces than a conventional patrol and an additional advantage was that raw data were available for reference . Using photographs, vehicle identification is positive and the time required seems competitive with the conventional approach . The third source of data on parking users was a selfadministered mail-back questionnaire . It consisted of four parts : • • • •
information on the last CBD-bound trip, by any mode ; information on parking in the last CBD-hound car trip ; socioeconomic and demographic data ; respondents' comments on parking in the centre of Jerusalem .
The questionnaire was distributed to a random sample of Jerusalem's car owners . Of 2600 questionnaires sent out, only 25% were returned . In addition, 940 questionnaires were handed to drivers entering their vehicles in the CBD parkCITIES August 1986
riaasril
Figure 2 . Jerusalem - study area . ing facilities . Of these, 22% responded . A total of 849 valid questionnaires were available . The major problem encountered in this survey is that, not only was the response rate low, the respondents represented a very biased sample of the population, which prohibited use of the sample for model estimation . The mean level of education, for example, was 15 years which is likely to be significantly higher than the mean of all car owners in Jerusalem . Moreover, it is plausible to assume that drivers who encounter greater problems in parking are more likely to respond to the questionnaire, and thus may present extreme information . However, the data are useful in demonstrating the importance of behavioural
CITIES August 1986
approaches in parking studies, as shown below . The analysis of the data presented below provided information on the patterns of CBD-bound trips in Jerusalem . parking at the trip-ends and, more relevant to the current context, some insight into the contribution of behavioural approaches to policy-oriented parking studies . Jerusalem's CBD is still a major attraction for trips, despite growing competition from suburban shopping centres . Much of the retail activity in the CBD is chained to other CBD-hound trips . Of shopping trips, 37% also included destinations for personal business (eg bank, hairdresser, lawyer etc) . About 12% of 205
Taaspalt
Figure 3 . Street parking in Jerusalem .
the work trips, which constituted 40%, of all ('1313-bound trips, included shopping as a secondary activity . Further suburbanization of workplaces may thus have a negative effect on CBD retail activity and the vitality of the city centre . Despite the general perception of a severe parking problem at the centre, the predominant mode of travel to the CBD by car owners is by the car (90%) . Only W X, reported using taxis and no bus trips were reported, despite the availability of a frequent and inexpensive service to the centre from many outlying districts . 'I his indicates that the current costs of driving
'space available for shoppers is reduced by commuters parking in the city centre' 'Paid in Israeli Shekels .
206
and parking, including the time loss associated with congested streets and the search for parking, are not strong deterrants to driving to the CBD . Improvements in public t ransportation . as observed in many Western countries, arc probably insufficient as an incentive to
encourage the use of high-occupancy vehicles, and disincentives to car usage are necessary if an observable change is desired . The recent introduction of more stringent enforcement of traffic regulations may help in this respect . Long-term parking (longer than four hours) occupies at least 12 %, of the available spaces . Consequently, space available for shoppers is reduced by commuters parking their cars in the city centre . That may not be to the benefit of the commuters who may have an interest in the viability of the city centre, but fail to identify the relationship between their parking and the activity level of the CBD . Such long-term parking is encouraged by the prevailing pricing structure . Payments for parking are of two types : municipal car parks and street parking require the use of parking cards which costs $0 .22 (US dollars) 12 and $0 .11 per hour, respectively . Parking is legally restricted to two hours, but riot strictly enforced, as the use of multiple one-hour cards is tolerated . Private car parks charge an average of $0 .65 per hour and CITIES August 1986
r usually lower rates for additional hours . If encouraging short-term parking is a desired policy goal then intervention is necessary, by both a change in the pricing schedules and enforcement . However . intervention in the pricing schedule of private car parks is legally complicated . The search for parking, according to the (biased) sample, is relatively long . Between 8 .00 am and early afternoon the median is over 9 minutes, although for most of the day (except between 8 :00 am and 09 :00 am) the mode is zero . One possible technique to reduce search time is the use of dynamic signalling which would divert drivers from searching in areas which are fully occupied . Parking location was found to be related to the direction of access to the CBD . Drivers are more likely to park on the side of the centre from which they approach the CBD . This seems to be encouraged by the traffic management system which directs the flow so as to avoid traffic crossing the centre . The potential contribution of a behavioural approach could ideally be demonstrated by the development of models which show the relationship between revealed behaviour and characteristics of the decision makers and the alternatives they face . However, due to the bias in the sample, the value of a behavioural approach can only he shown indirectly . To this end, the analysis was performed separately for various market segments . The identification of different behavioural patterns across market segments serves two purposes : such differences support the hypothesis that there is a correlation between the decision maker's individual characteristics and parking behaviour ; and second, it may make it possible to devise parking policies to apply to certain market segments . A number of market segments, that is groups within the sample who demonstrate similarities in behaviour, have been identified . First, a distinction can be made between people who work at the CBD and those working elsewhere . The former usually enter the CBD earlier in
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f
the day and occupy parking spaces for longer durations than the latter . Second, differences in behaviour associated with gender and education levels were observed . Women who work in the CBD were found to park for shorter durations than men, possibly because many of them work part-time . However, there is no difference in parking duration between males and females among non-CBD workers, Women's search for parking was shorter by about 20%, than that of men for both CBD and non-CBD employees as can he seen in Table 1 . A possible explanation is that women tend to search in areas or car parks which have lower probabilities of occupancy . In addition, women reported higher rates of delinquent parking (not using parking cards) than men, a fact that may provide additional explanation for their shorter search . While it is not suggested that
`parking is viewed as a "free public good" ' policies oriented towards, gender-based market segments he employed, their clear difference in behaviour demonstrates the relevance of demographic and socioeconomic factors in understanding parking behaviour . The perceived risk of enforcement of parking regulations seems to he generally low and hence more than 50% of the drivers have admitted at the time the questionnaire was collected that they do not use the cards where required . This has probably changed recently as wheel clamps have been introduced . Differences in behaviour were identified among people with varying levels of education (elementary, high school and university) . Search time was negatively correlated with education level . A possible explanation is that people of higher educational level have higher values of time and plan their schedules so as to avoid long searches . This explanation is supported by the fact that the difference 207
Tianspnlt Table 1 . Parking search time by workplace and sex (minutes). Working in Number of cases Mean Standard deviation Median Mode % zero search time
"T.
Schelling,
Micromolives and
Norton, New York . 1978 . 1O G . Miller and C . Everett, 'Raising commuter parking prices -an empirical study', Transportation, Macrobehavior,
Vol 11, 1982, pp 105129 .
208
CBD
Working outside Male Female
Male
Female
320 10 .5
106 8 4
168 11 4
86 8 .7
107 96 0 .0
9 .9 5 .0 0 .0
11 .0 9 .7 0 .0
8 .8 5 .3 0 .0
24 .1
27.4
19 .9
24 .4
CBD
is consistent, even when parkers who have zero search time, presumably parking in car parks with higher rates, are eliminated . Another important finding of this study relates to drivers' perception of the 'parking problem' . Drivers fail to identify the social costs of providing parking in terms of the consequential traffic congestion, air pollution, safety and energy consumption . Moreover, the costs of land and construction are not appreciated . Parking is viewed as a `free public good' which drivers believe should be supplied by the authorities . Hence, the solution suggested by the respondents most frequently relates to the construction of more facilities and the reduction of rates . None have admitted to recognizing the relationship between increases in parking supply and street congestion . Only a few respondents suggested measures which would curtail trips by car to the CBD . Parking problems are not detached from the political policy-making process and often they rank high in the agenda of urban politicians, precisely because they are considered important by drivers . Yet, rather than accepting public criticism, the fact that drivers do not recognize the real social costs of supplying parking in city centres should be given further attention . Although, due to the fact that there is a gap between micro-motives and macrobehaviour," a better understanding of
the costs may not have a profound effect on drivers' behaviour, it can at least be used by elected officials to divert pressuree from drivers' interest groups . This is particularly true for commuters who have business interests in the CBD and who should become aware of the conflict between their use of parking and the revenues losses caused by parking shortages for shoppers . The policy implication is that more efforts must be directed at estimating and publicizing the high social costs of car usage and parking in the CBD . Conclusions . Three types of conclusions can he drawn from this study . First, while the reasons for the differences between market segments are not all clear and may be the subject of separate research, the identification of market segments by socioeconomic and demographic attributes supports the hypothesis that a disaggregate approach is beneficial for purposes of policy formulation, as each segment is expected to react differently to policy measures . Experience in raising parking prices in Washington . DC, for example, has demonstrated the different reactions to policy measures . t4 While the segmentation chosen in the Jerusalem study may only be illustrative, the conclusion with regard to the importance of using a behavioural approach is still valid . Second, specific policy implications can be drawn, even if formal models are not estimated, but merely on the basis of the user level data . Third, methodological lessons are learned from this study with regard to data collection . Specifically, the innovative photographic method of identifying vehicle turnover rates seems to be more efficient than the conventional approaches . Yet, the collection of disaggregate user data by means of a selfadministered questionnaire is problemmatic when the expected response is likely to overrepresent certain interest groups .
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