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Publication Number: FHWA-RD-01-158
Date: March 2002
Study of Adequacy of Commercial Truck Parking Facilities
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This section contains an inventory of the number of public rest areas and commercial truck stops and travel plazas that could be used to comply with Federal HOS rules. The two primary data sources for the commercial vehicle parking supply information presented in this document are 1) the Interstate America database of commercial truck stops and travel plazas and 2) a survey of public agency rest areas conducted for this study. The inventory information presented herein is the most recently available and is generally characteristic of conditions in 1999 (in the case of the commercial truck stop database) and 2000 (in the case of the public rest area survey).
While this inventory does include the parking areas that are located close to the NHS and used most often by truck drivers, the inventory does not include parking that is available from other sources (e.g., restaurants and stores located close to the NHS, loading and unloading facilities). Table 1 lists the locations at which drivers reported last parking for rest and the relative frequency with which these locations were reported.
The inventory presented includes all the Interstates on the NHS and selected non-Interstate portions of the NHS with daily truck volumes of greater than or equal to 1,000. Information was gathered for each parking facility on each highway segment and summed to generate estimates of the parking supply for each highway segment.
A survey that included 49 States (excluding Hawaii) was conducted to gather information on truck parking capacity at public rest areas and welcome centers. Information was obtained from all 49 State DOTs and their toll road agencies for a combined total of 1,771 public rest areas. Information was compiled and entered into an electronic database for use in this study. The results for each State are summarized in table 9.
The “Parking Facilities” column of this table lists the total number of public rest areas identified in each State, and the “Parking Spaces” column lists the total number of parking spaces at those facilities. The “Weigh Station” column indicates whether the State allows parking at weigh stations, and the “Imposes Time Limits” column indicates whether the State imposes time limits on parking at public rest areas.
As can be seen from reviewing the results of table 9, some States permit drivers to use weigh stations for parking when the stations are closed. While this does create additional parking spaces for drivers, the estimated number of spaces created was not included in the analysis. During the driver surveys (summarized in section 2.2 > of this report), many drivers indicated that parking at a weigh station was not a desirable solution. These facilities often lack amenities, and concern was also expressed about parking at an enforcement facility. An additional constraint to estimating the number of parking spaces at these facilities is that weigh station hours of operation vary and rotate between daytime and evening operations. This variance meets the needs of the enforcement community, as it enables enforcement personnel to maintain random inspection patterns. However, this variance makes the availability of these facilities for use as parking spaces somewhat random. The study team determined that, based on these factors, weigh and inspection stations should not be considered as a supply source of parking spaces for the overall analysis.
Table 9. Commercial truck parking inventory: Public rest area facilities along interstates and other NHS routes carrying more than 1,000 trucks per day.
An additional consideration identified during the course of the survey is that 25 States indicated that they have time limits on the amount of time a truck may be parked at a public rest area. Of these, 9 States have limits that should have little impact on using the facilities for long-term rest to satisfy HOS rest requirements (e.g., the time limit is greater than 8 hours, the time limit applies only during the day), while the other 16 States have limits that might impact using the facilities for long-term rest. Of these 16 States, 10 enforce the time restrictions only rarely or never, leaving only 6 States sometimes enforcing time restrictions that might impact the use of the facilities for long-term rest.[a]
An analysis of the number of parking spaces at public rest areas along Interstate highways versus non-Interstate highways indicated a total of 28,396 spaces distributed along 39,963 miles of Interstate highways included in this study and 2,853 non-Interstate spaces distributed along 21,702 miles of non-Interstate highways.
Although not developed as part of the inventory process, researchers did develop an estimate of 1 percent annually for the expected growth rate of truck parking spaces at public rest areas. This estimate was derived from the response of the State partnerships regarding plans to improve public rest areas (see section 5.4.1). Fifteen States indicated that they have firm plans to provide additional parking spaces at public facilities, and 11 of these States provided a specific number of spaces for a total increase of 1,609 spaces at public facilities over the next 5 years. This increase of 1,609 spaces is 5.1 percent of the 31,249 current spaces, and a 5.1 percent increase over 5 years is equivalent to a 1 percent annual growth rate.
Commercial truck stops and travel plazas are designed to provide drivers an opportunity to fulfill many non-rest related activities, while public rest areas provide the driver with only minimal services. Commercial truck stop operators provide a number of services to trucks and typically provide extended parking to encourage drivers to use these services. In other words, commercial truck stop and travel plaza operators do not provide extended-stay parking as a primary service but only to encourage purchases of fuel, food, and other services. Truck stop operators do not generally charge for parking and provide parking only to attract business.
The primary data source for the inventory of commercial truck stops and travel plazas was the Truck Stops Database developed by Interstate America. FHWA, for purposes of this study, obtained a license permitting the use of the 1999 database. This database, which includes every known facility in the United States and Canada (for a total of 6,327 facilities), is updated annually and contains information describing the number of commercial vehicle parking spaces available at a facility as well as information about the amenities at that facility. Unfortunately, the number of truck parking spaces available is not expressed as an exact number, but as one of the ranges listed in table 10; this results in a range of possible values for the inventory of truck parking spaces for each highway segment rather than an exact number.
The commercial truck stops and travel plazas listed in this database were identified with the road segments that were the basis of the demand model calculations. The number of parking spaces for each road segment was determined by summing the spaces at each commercial truck stop and travel plaza for that segment. Because the number of truck parking spaces was reported as a range, this resulted in a minimum number of spaces (obtained by summing the bottom number of the range) and a maximum number of spaces (obtained by summing the top number of the range) when this database was used to evaluate the supply of truck parking.
Table 10. Parking capacity ranges from the Truck Stops Database
In an effort to better quantify shortages of truck parking spaces that may exist, some States completed a field inventory of the commercial parking facilities along the highway segments included in this study. This generated an exact count (i.e., the minimum and maximum number of spaces is the same) for the number of parking spaces available, and these exact counts were used in place of the ranges obtained from the truck stops database. The results of this inventory for each State are summarized table 11 The “Parking Facilities” column of this table lists the total number of commercial truck stop and travel plaza facilities identified in each State, and the “Parking Spaces” column lists the total number of parking spaces at those facilities.
An analysis of the number of parking spaces at commercial truck stops and travel plazas along Interstate highways versus non-Interstate highways indicated a total of between 153,829 and 260,599 spaces distributed along 39,963 miles of Interstate highways included in this study and between 13,705 and 24,002 non-Interstate spaces distributed along 21,702 miles of non-Interstate highways.
The expected growth of truck parking spaces at commercial truck stops and travel plazas is expected to be about 6.5 percent annually. This estimate was derived from an evaluation of the Truck Stops Database for the years 1997 to 2000 performed by the National Association of Truck Stop Operators (NATSO) Foundation. This evaluation found an historical growth rate of 6.5 percent for this period, and NATSO expects this growth rate to continue in the future.
3.4 Driver Assessment of Parking Facility Quality
The number of parking spaces is only part of the issue related to the adequacy of the supply of truck parking spaces. For example, if sufficient spaces are available yet these spaces are either difficult to access or do not have the amenities that a driver needs, then a driver may choose to park at an over-crowded facility, may park at an inappropriate location, or may drive while tired to find a more favorable facility. This section summarizes the results from the driver survey (see section >2.2 )that indicate truck drivers’ assessments of the quality and availability of truck parking facilities.
Table 11. Commercial truck parking inventory: Commercial truck stop and travel plaza facilities along interstates and other NHS routes carrying more than 1,000 trucks per day.
Drivers were asked to report how frequently truck parking spaces have certain usability characteristics. Drivers rated how frequently available parking is convenient to the highway, has the features they need, has time limits that allow enough time for their needs, has enough room for them to maneuver their trucks in and out, and is used only by trucks. Respondents gave mixed ratings for all these usability characteristics (table 12). For each of these usability characteristics, sometimes [encountered] was the most frequently reported driver response. The usability characteristic that was most often encountered by respondents (i.e., most often given ratings of frequently or almost always) was available parking has the features I need, marked by 51 percent of respondents. Thirty-nine percent of respondents indicated that available parking is frequently or almost always convenient to the highway.
Table 12. Driver-reported usability characteristics in truck parking.
To help clarify drivers’ parking preferences, the survey asked drivers to identify how important various parking facility features are to them when they park their trucks. Drivers rated various features on a scale from one to five (almost always important to almost never important). Table 13 shows the features evaluated, along with the mean and modal ratings they received. Features rated as most important were generally the ones that address basic needs. Food, fuel, restrooms, phones, showers, convenience to highway, and well-lighted parking lots all received modal ratings of almost always important. In fact, between 70 and 85 percent of the sample rated these features as frequently or almost always important. Interestingly, drivers appear to value well-lighted parking lots more than they value security presence. Seventy-five percent of respondents rated “well-lighted parking lots” as frequently or almost always important, while only 60 percent gave the same ratings to “security presence.” The majority of drivers rated features such as entertainment facilities, Internet connections, and availability of travel information as less important.
Almost 400 respondents provided written comments on the parking facility features they consider important. The single most frequently mentioned feature was big parking spaces that allow trucks to maneuver in andout (written by 45 drivers). Drivers indicated that they look for quiet parking facilities where they are not likely to be disturbed by police officers or solicitors. They value clean facilities where the personnel are friendly. Drivers also commented that they prefer parking facilities that allow access to shopping areas with grocery or department stores. Finally, drivers commented that laundry facilities add to the appeal of a parking facility.
Ratings given by short-haul drivers reflected the fact that they value parking facility features differently than long-haul drivers. Specifically, long-haul drivers most often rated features such as showers, fuel, and well-lighted parking lots as almost always important, while short-haul drivers most often rated these same features as only frequently important. Female respondents provided different ratings than their male counterparts on some features. Eighty percent of women rated security presence as frequently or almost
Table 13. Driver-rated importance of features when parking.
always important, while just under 60 percent of men gave the same ratings to security presence. Additionally, 92 percent of women rated “well-lighted parking lots” as frequently or almost always important, while about three-quarters of men did the same.
In addition to inquiring about the features that are important to drivers, the survey also asked which type of parking facilities (public versus commercial) they prefer for parking. Because parking facility preference likely depends on the purpose of the stop, various common “reasons for parking” were identified to give context to their facility preferences. Generally when drivers showed a preference, they indicated a preference for commercial truck stops over public rest areas (table 14). Public rest areas were preferred to commercial truck stops only when drivers stopped for a quick (less than 2-hour) nap. For extended rest (more than 2 hours), performing minor truck maintenance, and eating a meal, drivers overwhelmingly preferred truck stops to rest areas, with between 79 and 91 percent of drivers indicating a preference for truck stops and fewer than 6 percent indicating a preference for rest areas. Most respondents marked no preference for stops made to use vending machines, get travel information, use public phones, and use the restroom. However, among those drivers who did show a facility preference when making these types of stops, more drivers indicated a preference for truck stops. For all the parking reasons listed, short-haul driver preferences were the same as long-haul driver preferences.
Table 14. Drivers’ parking facility preferences by purpose of stop.
An important factor in determining whether there is a sufficient supply of truck parking spaces involves the concept of interchangeability of spaces at public rest areas and commercial truck stops and travel plazas. That is to say, can a surplus of parking spaces at commercial truck stops and travel plazas compensate for a shortfall in available public rest area parking? Because most truck drivers use public rest areas and commercial truck stops and travel plazas for resting, it is logical to conclude that a driver can rest equally well while parked at a public rest area or at a commercial truck stop or travel plaza and, therefore, that these spaces are interchangeable. This view is challenged, however, by the results of the national survey of driver needs and preferences, by the findings of field observational studies, and by the imbalance identified within the supply and demand ratios between public and commercial parking spaces.
Drivers’ responses to the Truck Parking Needs and Preferences Survey conducted as part of this study demonstrated definite preferences and priorities when it comes to choosing where they will park. These preferences are offered as evidence of the limited interchangeability or substitutability between public rest areas and commercial truck stops or travel plazas.
When drivers park for quick naps (less than 2 hours), they prefer to park in public rest areas (45 percent of the drivers preferred a public rest area, 19 percent preferred commercial truck stops, and 36 percent expressed no preference between public rest areas and commercial truck stops). For more lengthy activities (greater than 2 hours), such as eating a meal, resting for the night, or repairing a truck, drivers choose truck stops where possible (79 percent of the drivers preferred a truck stop, 6 percent preferred rest areas, and 16 percent expressed no preference between rest areas and truck stops).
To help clarify drivers’ parking preferences, the survey asked drivers to identify how important various parking facility features are to them when they park their trucks. Restrooms, convenience to highway, showers, well-lighted parking lots, and public phones were the top features selected from a list of 14 features that drivers rated as most important. Three of the five features address drivers’ basic needs, while the other two clearly address drivers’ preferences. Drivers were also given the opportunity to write comments on the parking features they consider most important. The single most frequently mentioned feature was big parking spaces that allow trucks to maneuver in and out.
The survey also provided the respondents with the opportunity to speculate about why truck drivers sometimes park on entrance or exit ramps and highway shoulders. The most commonly reported reasons were that no nearby parking facility was available, no empty spaces were available at nearby truck stops or rest areas, nearby parking spaces have time limits that are too short, empty parking spaces nearby were blocked by others vehicles, the ramp/shoulder is convenient for getting back on the road, interruptions by strangers (e.g., drug dealers, prostitutes) were less likely, it is hard to drive around congested parking lots, and better lighting exists on ramp(s)/shoulder(s) than in lot(s).
In addition to the driver self-report data cited above, more objective evidence to support the notion of limited interchangeability between public rest areas and commercial truck stops and travel plazas can be found from the results of observational field surveys conducted both for this study and by a number of States.
Commercial vehicle parking field surveys were conducted as part of the demand model development effort for this study. The purpose of these observational studies was to record trucks parked during the peak hour in public rest areas, commercial truck stops, pull-out areas, interchange ramps, mainline and cross-street shoulders, fueling stations, fast food restaurants, hotels, etc. The studies were conducted along three segments of NHS highway in Arkansas, six segments in Georgia, seven segments in Idaho, two segments in Mississippi, one segment in Missouri, six segments in Pennsylvania, two segments in Tennessee, and two segments in Virginia. These segments were selected as representing the typical range, from low to high, of truck parking supply and demand. Although most of the rest areas were full or overflowing, some of the commercial truck stops had spaces available, as did most of the fast food restaurants, fueling stations, and shopping centers along the segments, suggesting that drivers do differentiate between parking at public rest areas and other commercial parking areas.
The University of Tennessee conducted nighttime observational studies at all public rest areas in Tennessee for each day of the week.(7) Availability of space in commercial truck stops and travel plazas near interchanges was also examined. The results of the occupancy studies showed that the rest areas were overflowing with trucks at night, as evidenced by trucks parked along the shoulders of highway exit and entrance ramps as well as on interchange ramps. While the rest areas were overflowing, approximately 30 percent of the private truck parking spaces were not occupied, and the unoccupied private parking spaces outnumbered the trucks parked along the highways by nearly three-to-one. To understand why some truck drivers park along the highway when there are available private parking spaces, in-depth interviews were held with drivers. The opinions of the drivers interviewed were quite consistent. The findings were that commercial truck stops and public rest areas are not substitutes for each other because they meet different needs.
The State of Iowa completed field observations of truck parking on Interstate highways in 1999.(8) This study divided the Interstates in Iowa into six segments. Parking at public rest areas was observed to be above capacity for almost every segment and almost every day during the observation period, and trucks were observed parking on the shoulder at exit and entrance ramps. On the other hand, parking at commercial truck stops and travel plazas was observed to be above capacity for only a single segment, and then for only two of the seven days during the observation period. These observations suggest that drivers do differentiate between parking at public rest areas and other commercial parking areas.
In 1999 the Baltimore Metropolitan Council sponsored a study of truck parking in the Baltimore area that concluded that, even though there was a sufficient supply of parking spaces available to truck drivers, trucks were often parked illegally along the highways at night.(15) These observations suggest that truck drivers do differentiate between parking spaces by choosing to park in illegal spaces along the highway rather than legally at other locations.
FHWA supported a study in 1996 that included observations of truck parking along a stretch of I‑81 between Radford, VA, and Knoxville, TN.(1) These observations indicated that public rest areas tended to fill up quickly, reaching capacity before commercial truck stops. These findings suggest that truck drivers differentiate between parking at public rest areas and other commercial parking facilities.
As stated earlier in this report, the national driver survey was also used to develop an estimate of public and private parking demand to reflect drivers’ preferences for the two facility types. Drivers were asked, for each of seven activities, if they preferred to use public or commercial facilities. The relative preference for the two facility types was estimated by taking an average of the preferences for each activity, weighted by the duration of that activity. The results showed the proportions of total hourly parking demand for public rest areas and commercial truck stops to be 0.23 and 0.77, respectively. Therefore, if drivers had their preference, 23 percent of the total truck hours of parking demanded in a day (or the peak hour) would occur at public facilities, while the remaining 77 percent of the total truck hours of parking demand would occur at commercial facilities.
An assumption made in the modeling process, to convert 24-hour parking demand to peak-hour parking demand, was that a truck will occupy a space for at least 1 hour. While this assumption may not hold for daytime hours, the majority of trucks parked in the overnight peak hours are parked for longer periods of time in accordance with the HOS regulations. With this assumption in mind, due to the multiplicative nature of the model’s parameters, the proportions of hourly parking demand for public and commercial facilities can be directly compared to the proportions of parking supply at these two types of facilities. On average, only about 10 percent of the total available parking supply is at public facilities, while around 90 percent of the available parking supply is at commercial facilities. This imbalance in supply (10 percent at public facilities and 90 percent at commercial facilities) and demand (23 percent at public facilities and 77 percent at commercial facilities) is further evidence on the limits of interchangeability from the driver’s perspective.
In summary, while it may be argued that, because truck drivers could rest equally well at public rest areas and commercial truck stops and travel plazas, parking spaces at these two different types of rest stops are interchangeable. In other words, truck stop parking can be substituted for rest area parking, even if the private parking is not as convenient. On the other hand, empirical evidence provided through both driver surveys and observations of parking behavior indicate that parking at these locations is not interchangeable; more likely, the evidence suggests that there is some interchangeability and that this interchangeability is limited due to preferences expressed by drivers for one type of space over another. In reality, a system of parking exists in this country that consists of public rest areas, commercial truck stops and travel plazas, weigh stations, and various commercial establishments (motels, fast food restaurants, etc.). As a system, a certain synergy applies such that substitution occurs among the available types of spaces. However, it is not a complete substitutability. The interchangeability of one type of parking space for another is limited or governed by an array of factors that affect driver preferences (e.g., purpose of the stop, amenities available, parking convenience, time of day, hours since last slept, distance to next pickup/delivery), and these are the factors that influence a driver’s decision as to where to park.
Topics: research, safety, freight/goods movement
Keywords: research, safety, commercial motor vehicles, truck stop, rest area, travel plaza, truck parking, TEA-21 Section 4027 study, human factors, parking studies, parking supply, truck driver survey, parking demand model
TRT Terms: Soil mechanics--Mathematical models--Handbooks, manuals, etc, Shear strength of soils--Testing--Computer simulation--Handbooks, manuals, etc, Foundation soils, Roadside structures, Soil structure interaction, Finite element method, Impact loads, Computer models