May 2005 DOT HS 809 846 DOT HS 809 846 

12 & 15 Passenger Vans Tire Pressure Study:

Preliminary Results

Kristin K. Thiriez, Eric Ferguson, Rajesh Subramanian*

Traffi c Safety Facts

Research Note

Traffi c Safety Facts raffic Safety Facts

NHTSA’s National Center for Statistics and Analysis 400 Seventh St., S.W., Washington, D.C. 20590

* Kristin K. Thiriez is a Special Studies Project Engineer employed by Calspan Corporation, a contractor working for the Crash Investigations Division of the National Center 

for Statistics and Analysis, National Highway Traffi c Safety Administration. Eric Ferguson is a General Engineer in the Crash Investigations Division. Rajesh Subramanian is a 

Programmer Analyst in the Mathematical Analysis Division of NCSA.

1

 NHTSA Action Plan for 15-Passenger Van Safety, November 2004 Update, http://www.nhtsa.dot.gov/cars/problems/studies/15PassVans/15passvan.html

2

 Research Notes and Reports from NCSA’s Tire Pressure Special Study (DOT HS 809 315, DOT HS 809 316, DOT HS 809 317, DOT HS 809 359, and DOT HS 809 366) can 

be found at http://www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/availinf.html The analysis conducted on TPSS data to evaluate Tire Pressure Monitoring Systems was 

published at ESV 2003 (Paper Number 259) and can be found at http://www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/ESV2003.html

Summary

The National Highway Traffi c Safety Administration’s (NHTSA) 

National Center for Statistics and Analysis (NCSA) conducted 

a 15-passenger van tire pressure study. The purpose of the 

study was to determine the extent of underinfl ation and 

observe the tire condition in 12- and 15-passenger van (and 

vans with similar body styles) tires. The following topics are 

covered in this research note: sampling, data collection 

methodology, analysis and results.

Background

Crashes involving 12- and 15-passenger vans have raised 

concern about the safety of these vehicles among the 

public and NHTSA. In March 2003, Senator Olympia 

Snowe introduced the Passenger Van Safety Act of 2003, 

in the Senate. This bill, S.717, called on NHTSA to develop 

a dynamic test to assess the rollover risk of 15-passenger 

vans for a consumer information program; test 15-passenger 

vans at different load levels as part of the rollover resistance 

program of the NHTSA’s New Car Assessment Program 

(NCAP); and test and evaluate the stability control and other 

technological systems that may assist drivers in controlling 

15-passenger vans under conditions that may cause vehicle 

rollover. A similar bill was introduced by Representative Mark 

Udall in the House, H.R. 1641.

The National Transportation Safety Board (NTSB) has also 

issued a series of recommendations related to 15-passenger 

van safety. NHTSA developed a 15-Passenger Van Action 

Plan that addresses these recommendations. As part of its 

15-Passenger Van Action Plan, the agency decided to study 

the extent of underinfl ation in 12- and 15-passenger vans 

through the infrastructure of NCSA’s National Automotive 

Sampling System (NASS).

In support of rulemaking activities mandated by Section 13 

of the Transportation Recall Enhancement, Accountability, 

and Documentation Act, the NCSA conducted the Tire 

Pressure Special Study (TPSS) in February 2001 and the 

Tire Pressure Monitoring System Study (TPMSS) in 2003. 

The TPSS was designed to assess to what extent passenger 

vehicle operators are aware of the recommended tire 

pressures for their vehicles, the frequency and the means 

they use to measure their tire pressure, and whether and how 

signifi cantly the actual measured tire pressure deviated from 

the manufacturer’s recommended tire pressure. The TPMSS 

was designed to compare the extent of underinfl ation of 

vehicles equipped with TPMS to vehicles not equipped. 

The current Van Tire Pressure Study (VTPS) was designed 

to collect similar information to that collected in TPSS, but 

for 12- and 15-passenger vans (and vans with similar body 

styles).

Please refer to previous publications2 for results from both 

of these studies and analyses of that data to estimate the 

effectiveness of indirect and direct TPMS.

The TPSS results showed that 27% of passenger cars in the 

United States had at least one signifi cantly underinfl ated tire (for 

the purposes of this research note, “signifi cant underinfl ation” 

is defi ned as 25% or more below placard). The data also 

showed that less than 25% of the study participants were 

aware of where to fi nd the recommended tire pressure for their 

vehicles. NHTSA used this data in support of its rulemaking 

for Federal Motor Vehicle Safety Standard (FMVSS) No. 138, 

Tire Pressure Monitoring Systems. 
NHTSA’s National Center for Statistics and Analysis 2 400 Seventh St., S.W., Washington, D.C. 20590

Sample Design

The VTPS was designed as a 

convenience sample to capture a good 

representation of multiple regions, 

climates, and demographics. Data was 

collected from 16 locations throughout 

the United States. These locations were 

distributed among urban, suburban, 

and rural locations and were located 

in the east, midwest, southwest, and 

western United States. Estimates 

of the number of registered vans in 

specifi c targeted states were found 

using RL Polk (a private company that 

provides automotive data and market 

information) registration data.

The VTPS sample was selected from 

several different types of organizations. 

The study targeted some locations with 

only one vehicle and some locations 

with a fl eet of vehicles. Manufacturers 

of the vans included Ford, General 

Motors, and Dodge.

Table 1 - Distribution of 

Vehicle Organizations Sampled 

in the VTPS

Organization Type Sample

Colleges and Universities 13%

Churches and Community 

Groups 24%

Camps and Daycares 11%

Subtotal 48%

Vanpools 11%

Transportation and Limo 

Services 13%

Subtotal 24%

Local Governments 7%

Military 1%

Subtotal 8%

Hotels 5%

Subtotal 5%

Other (individuals, etc.) 14%

Subtotal 14%

Total* 99%

*Total not 100% due to rounding.

Source: National Center for Statistics and Analysis, 

National Highway Traffic Safety Administration

The agency chose to focus on 

moderately to fully-loaded vehicles 

and those that are used to transport 

children and young adults. Church and 

community groups, universities and 

colleges, day care facilities, and camps 

made up 48% of the sample, see Table 

1 (vans were not loaded when tire 

pressure measurements were taken). 

The distribution of vehicles shown in 

Table 1 is from a convenience sample 

and does not represent the true 

proportions of these vehicles in the 

United States. Extents of underinfl ation 

were analyzed and the results are shown 

in this research note. Data collection 

took place in spring and early summer 

of 2004. [Note: One would expect to 

fi nd more underinfl ation during the cold 

winter months due to the temperaturerelated drop in tire pressure.]

The total number of vehicle inspections 

completed was 1,242, with 937 15-

passenger vans.

Data Collection Methodology

Field data collection was conducted 

through the infrastructure of NCSA’s 

National Automotive Sampling System 

(NASS). 

Researchers visited organizations on 

weekdays during business hours. If a 

researcher contacted the owner of a 

vehicle by phone before an inspection, 

the researcher explained the study 

was related to van maintenance or 

“safety systems.” In order to keep the 

study from being biased, “tire” and 

“tire pressure” were not mentioned in 

the phone contacts with the potential 

participants.

The pilot phase of the data collection 

was conducted from April 26, 2004 

through May 14, 2004. Full-scale data 

collection was conducted from May 

17, 2004 through June 25, 2004. The 

vans inspected in the pilot phase were 

included in the fi nal VTPS data. Vehicles 

surveyed included 15-passenger vans, 

12-passenger vans, 14-passenger 

vans, and cargo vans with similar 

Gross Vehicle Weight Ratings (GVWR) 

and body styles. 

Nine anecdotal interviews were 

conducted to get an idea of the tire 

maintenance, driver training, and 

safety awareness of the managers 

of a subsample of our vehicles. The 

interviewees included vehicle fl eet 

managers from 2 churches, 2 colleges, 

a community organization, a hotel, a 

daycare, a transportation company, 

and a vanpool company. 

The Vehicle Inspection Form, which 

was completed for each observation, 

contained vehicle profi le information 

such as make, model, and model 

year. It also contained information 

documented from the vehicle’s placard 

regarding recommended tire size, 

recommended infl ation pressure, and 

the Gross Axle Weight Ratings.

The Tire Inspection Form, which was 

also completed for each tire (except 

unmounted spare tires), contained tire 

size and measurement information, and 

a variable to document visible evidence 

of tire aging and/or damage (loose 

tread, sidewall rot, etc.). 

At the conclusion of each observation, 

the participant was given a “courtesy 

card” which contained the infl ation 

pressure measured on each tire, the 

vehicle manufacturer’s recommended 

cold tire pressure, and several tire 

safety tips.

Special Equipment

Special equipment used for data 

collection included a pyrometer to 

measure tire sidewall temperature and 

ambient air temperature, an air pressure 

gauge, and a tread depth indicator to 

measure tread depth. 

Analysis

Good tire care improves vehicle 

handling3 as well as fuel effi ciency 

and tire life. Proper tire maintenance 

can prevent such events as tread 

separations and tire blowouts which 

may cause loss of control of a vehicle, 

when not handled properly, and result 

in a rollover. Low tire pressure can 

also increase stopping distances and 

the chance of hydroplaning on wet 

surfaces. 

3

 “Testing the Effects of TPMS Minimum Activation Pressure on the Handling and Rollover Resistance of a 15-Passenger Van”, Garrott and Forkenbrock, DOT HS 809 701, 

 June 2004
NHTSA’s National Center for Statistics and Analysis 3 400 Seventh St., S.W., Washington, D.C. 20590

Data were collected on over 1,200 

vehicles during the VTPS. An analysis 

was performed looking at the 

percentage of the vans that had at least 

one signifi cantly underinfl ated (25% or 

more from placard pressure) tire. 

The variables of interest in determining 

the underinfl ation are the recommended 

pressures for each vehicle and the 

measured pressures for each vehicle. 

These were compared to determine 

the extent of misinfl ation (misinfl ation 

is used to characterize the extent of 

underinfl ation and/or overinfl ation) for 

each tire and then for each vehicle as a 

whole. The data were used to determine 

both underinfl ation and misinfl ation 

(overinfl ation was included because 

indirect tire pressure monitoring 

systems do not distinguish between 

over and underinfl ation).

Results

For the purposes of this research 

note, underinfl ation was determined by 

comparing measured pressures to the 

vehicle manufacturer’s recommended 

pressures. It should be noted that the 

vacated FMVSS No. 138, the regulation 

that required TPMS, listed minimum 

activation pressures (MAP) for the 

warning lamp to illuminate. For Load 

Range E rated tires, this MAP value was 

46 psi (320 kPa). The VTPS found that 

16% of the 15-passenger vans in the 

study had recommended pressures 

below this MAP value. Nonetheless, 

underinfl ation was determined relative 

to the recommended pressure.

VTPS found that 56% of all vans had 

at least one tire underinfl ated by 25% 

or more, see Table 2. That is more than 

double the percentage of passenger 

cars we found in the TPSS (TPSS 

is a national estimate, while VTPS 

is a convenience sample, so true 

comparisons are not possible).

Table 2 - Percent of Vehicles 

in the VTPS and TPSS with 

at Least One Tire Improperly 

Infl ated

Vehicle

Misinfl ated 

by 25% or 

More

Underinfl ated 

by 25% or 

More

15-

Passenger 

Vans

74% 57%

Other Vans 68% 54%

All Vans 72% 56%

Light 

Trucks 

from TPSS

39% 29%

Passenger 

Cars from 

TPSS

39% 27%

Source: National Center for Statistics and Analysis, 

National Highway Traffic Safety Administration

For all tables in this research note, 

“Other Vans” include 12-passenger, 

14-passenger, and cargo vans. This 

study also compared the percentage of 

vans that had all four tires signifi cantly 

underinfl ated to light trucks and 

passenger cars found in the TPSS. 

Table 3 shows that 6% of vans (a rate 

double that of passenger cars) had 

all four tires underinfl ated by 25% or 

more.

Average underinfl ation was calculated 

by fi nding the worst underinfl ated tire 

for each vehicle and then taking the 

average of all vehicles. The average 

underinfl ation of vans was 29% under 

the recommended pressure; vehicles 

with overinfl ated tires were included as 

vehicles with zero underinfl ation for this 

calculation. The average misinfl ation 

(also using the worst misinfl ated tire 

per vehicle) of vans was 35% from the 

placard pressure.

Table 3 - Percent of Vehicles 

in the VTPS and TPSS with All 

Four Tires Improperly Infl ated

Vehicle

Misinfl ated 

by 25% or 

More

Underinfl ated 

by 25% or 

More

15-

Passenger 

Vans

7% 4%

Other Vans 11% 9%

All Vans 8% 6%

Light 

Trucks from 

TPSS

7% 4%

Passenger 

Cars from 

TPSS

6% 3%

Source: National Center for Statistics and Analysis, 

National Highway Traffic Safety Administration

Because it was learned from all three 

of our tire studies that people use the 

pressure indicated on the tire sidewall 

as a guide when checking their tire 

pressure, the study also analyzed 

overinfl ation. It was found that 22% of 

vans had at least one tire overinfl ated 

by at least 25% of the recommended 

pressure. This can be explained by the 

large difference between the placard 

recommended front pressure (typically 

45 or 55 psi) and the maximum 

pressure listed on the tire sidewall 

(80 psi). Two out of 9 interviewees 

said that they looked at the sidewall 

to determine infl ation pressure. The 

rear recommended pressures were 

typically 80 psi, so overinfl ation due 

to referencing the tire sidewall was not 

seen here. See Table 4 for results.

Not only were vehicles overinfl ated 

when compared to recommended 

pressure, but many were infl ated past 

the maximum pressure recommended 

on the tire sidewall. Seven percent of 

the vans had at least one tire infl ated 

past the maximum pressure on the tire 

sidewall. 31 vehicles had at least one tire 

that was more than 5% over maximum 

pressure; 14 vehicles were more than 

10% over maximum pressure, and 4 

vehicles were more than 20% over 

the maximum pressure, which is more 

than 16 psi over the maximum pressure 

allowed.
NHTSA’s National Center for Statistics and Analysis 4 400 Seventh St., S.W., Washington, D.C. 20590

play a part in vehicle handling. In the TPSS, it was found 

that underinfl ation was more prevalent in older vehicles. This 

study produced a similar result.

The study found that 4% of vans had at least one tire with 

visible evidence of aging and/or damage. The study also 

examined the tires’ tread depth and found that 6% of the 

15-passenger vans had at least one bald tire (2/32nds of an 

inch or less). 18% of the 15-passenger vans had 4/32nds of 

an inch or less of tread. See Table 5 for these results. Worn 

tread has been linked with increasing underinfl ation2.

Table 4 - Percent of Vehicles in the VTPS with at 

Least One Tire Overinfl ated

Vehicle Overinfl ated by 

25% or More

Overinfl ated Past 

Max Pressure

15-Passenger Vans 23% 6%

Other Vans 18% 8%

All Vans 22% 7%

Source: National Center for Statistics and Analysis, National Highway Traffic Safety 

Administration

So far, the analysis has shown the percentage of vehicles 

with at least one underinfl ated tire, one overinfl ated tire, or 

one-misinfl ated tire. It is interesting to note that 6% of the 

vans had both signifi cant underinfl ation and signifi cant 

overinfl ation in the same vehicle.

Because vehicle handling characteristics differ depending 

not only on infl ation pressures, but the location of misinfl ated 

tires, the fi gure shows the distribution of misinfl ation by tire 

location.

Figure 1 shows that underinfl ation is more of a problem with 

tires on the rear axle. 50% of rear tires were underinfl ated 

past the 25% threshold while between 8 and 9% of front tires 

were underinfl ated past the 25% threshold. Keep in mind that 

the typical recommended pressure for the rear tires is 80 psi, 

while for the front they are between 45 and 55 psi.

In addition to tire pressure, the age and wear of a tire also 

28%

30%

32%

34%

36%

38%

2004 Source: National Highway Traffic Safety Administration, National Center for Statistics and Analysis. Average Underinflation

22%

24%

26%

20022000

1998

1996

19931991

1989

14%

12%

10%

8%

6%

4%

2%

0%

Underinflation Overinflation

Percent Misinflation

Right Front Tire Left Front Tire Right Rear Tire Left Rear Tire

-90%-80%-60%-40%

-20%

0%

20%

40%60%80%

100%

Percent of Vehicles

Figure 1 - All Vans Percent Distribution of Misinfl ation

Figure 2 - A Figure 2 - Average Underinfl ation by Model Year verage Underinflation by Model Year
NHTSA’s National Center for Statistics and Analysis 5 400 Seventh St., S.W., Washington, D.C. 20590

Table 5 - Percent of Vehicles in the VTPS with at Least One Tire 

Below Certain Tread Depth

Vehicle

Tread Depth of 2/32nds 

of an inch or less 

(% of vehicles)

Tread Depth of 4/32nds 

of an inch or less 

(% of vehicles)

15-Passenger Vans 6% 18%

Other Vans 5% 17%

All Vans 5% 18%

Passenger Cars from TPSS 9% 34%

Source: National Center for Statistics and Analysis, National Highway Traffic Safety Administration

Conclusion

The data from this study show that a very high percentage of large vans have 

signifi cantly underinfl ated tires, a much larger percentage than passenger cars. 

This poor tire maintenance in combination with the conditions under which these 

vehicles are driven (i.e. transporting groups of children, inexperienced drivers, etc.) 

suggest a need for better van tire safety awareness. Six of the 9 interviewees were 

familiar with the NHTSA advisories on 15-passenger vans. Research into potential 

countermeasures to improve van safety might include improving driver training, 

equipping vehicles with a tire gauge, requiring passengers to wear safety belts, and 

removing the last row of seats. 

Other possible countermeasures to poor tire pressure might include the integration 

of tire pressure monitoring systems into 12- and 15-passenger vans. Regardless of 

the presence of TPMS, public awareness of proper tire maintenance is key to the 

improvement of tire condition. Each tire, including the spare, should be checked 

monthly when cold and set to the recommended infl ation pressure as specifi ed on 

the vehicle placard and in the owner’s manual.

For additional copies of this research 

note, please call (202)934-8517 or fax 

your request to (202)366-3189. For 

questions regarding the data reported 

in this research, contact Eric Ferguson 

[202-366-9430] of the National Center 

for Statistics and Analysis. This research 

note and other general information on 

highway traffi c safety may be accessed 

by internet users at: http://www-nrd.

nhtsa.dot.gov/departments/nrd-30/

ncsa/.
NHTSA’s National Center for Statistics and Analysis 6 400 Seventh St., S.W., Washington, D.C. 20590