U.S. Department of Transportation 1200 New Jersey Avenue SE., Washington, DC 20590

National Highway Traffic Safety Administration

Traffic Safety Facts

Traffic Tech – Technology Transfer Series

Number 384 April 2010

Pilot Tests of a Seat Belt Gearshift Delay on the 

Belt Use of Commercial Fleet Drivers

Wearing a seat belt has been shown effective in avoiding 

or reducing serious injury due to traffic crashes. While 

belt use rates in the United States increased from under 

60% in 1994 to 83% in 2008, a substantial number of drivers still drive unbelted. Current efforts to increase seat belt 

use focus primarily on high-visibility enforcement campaigns, public education, and seat belt reminder systems. 

NHTSA investigated a novel engineering approach using 

a gearshift delay to increase belt use among commercial 

drivers in the United States and Canada. 

A car with automatic transmission cannot shift into gear 

if the vehicle senses that the brake lights are not lit, meaning that the driver must have a foot on the brake pedal. 

This safety feature was designed to prevent vehicles from 

accelerating unintentionally after being placed into drive

or reverse. For this study, a relatively simple change to the 

software code allowed the system to make an additional 

check before the vehicle can be placed into drive. Specifically, at the same time as the brake light check occurs, 

the vehicle’s computers checked to see if the driver was 

belted. If the driver was not belted, a gearshift-seat belt 

delay system prevented the driver from shifting out of 

park for several seconds.

The timing of the reminder system was designed to prompt 

drivers before they started driving to avoid the possibility 

of stimulus overload as they negotiated their way into traffic, a trip segment associated with high cognitive demand. 

This timing should allow most drivers sufficient time to 

buckle up, thereby avoiding the prompt. It also had the 

safety benefit of prompting unbuckled drivers before they 

placed their vehicles in motion.

Method

The seat belt-gearshift system was tested with a fleet of 

60 U.S. and 60 Canadian vehicles from a variety of government agencies and the private sector. Vehicles were 

instrumented with the gearshift-seat belt delay system 

and data loggers to record seat belt use. Belt use was 

monitored across three phases: Baseline-1, Intervention, 

and Baseline-2. Each phase lasted several weeks and 

the delay was active only during the intervention. Half 

of each fleet was randomly assigned to receive a fixed 

(8-second) or variable (8-second average, 4- to 19-second 

range) gearshift delay. 

Results 

As expected, seat belt use increased during the intervention phase when the gearshift delay was active. In both 

fleets, belt use was significantly higher during the intervention period relative to Baseline-1. There were no differences in belt use between delay types (fixed versus 

variable). Table 1 shows average belt use, with standard 

deviations in parentheses, for the three study phases. 

Belt use at the intervention phase increased an average 

of 20 percentage points for the treatment groups. Belt use 

appeared to decline during Baseline-2, but the drop was 

not statistically significant. In three of the four groups, belt 

use remained higher than at the beginning of the study.

Table 1. Percent of Belted Trips per Day, by Country and 

Study Phase

Baseline-1 Intervention Baseline-2

United States

% Belted Trips

Fixed 41.7(28.2) 69.9(27.1) 61.6(33.9)

Variable 54.4(27.9) 64.8(29.9) 51.9(31.4)

Canada

% Belted Trips

Fixed 51.92(33.75) 72.4(23.38) 61.0(31.4)

Variable 55.88(26.98) 76. 6(17.40) 67.4(22.6)

Figure 1 presents these results in graphic format. In the 

United States and Canada, belt use increased significantly 

when drivers were faced with experiencing the gearshift 

delay when they did not buckle up. 
TRAFFIC TECH is a publication to disseminate information about 

traffic safety programs, including evaluations, innovative programs, and new publications. Feel free to copy it as you wish. If you 

would like to receive a copy, contact Angela H. Eichelberger, Ph.D., 

Editor, fax 202-366-7394, e-mail: angela.eichelberger@dot.gov.

1200 New Jersey Avenue SE., NTI-132

Washington, DC 20590

Figure 1. Seat Belt Use by Treatment Period and Country

0%

10%

20%

30%

40%

50%

60%

70%

80%

Baseline1 Intervention Baseline2

Treatment Period

Mean Percentage of 

Belted Trips

U.S. Canada

Unintended Belt Removal 

An example of an unintended behavioral adaptation 

would be if drivers removed their seat belts more during the intervention phase than during the first baseline. 

The data logger, however, recorded very few instances 

of drivers removing their seat belts during trips. During 

the Baseline-1 and Intervention periods, seat belt removal 

averaged less than 1% for the United States group. Canadian commercial drivers removed their belts slightly more 

often than U. S. drivers, but removal rates were still very 

low, ranging from 4.2% to 1.6%, across the different conditions of the study. These percentages clearly indicate that 

the intervention phase was not associated with a higher 

removal rate than the baseline periods; drivers who buckled initially tended to remain buckled. 

Commercial Drivers’ Reactions 

The study ended with a focus group asking commercial 

drivers for their feedback about the gearshift delay systems. Topics of interest included perceived system effectiveness, ability to bypass, usefulness for teenage drivers, 

annoyance, and acceptance. While focus groups do not 

produce representative data, most drivers indicated that 

the system increased their belt use, although a few drivers 

reported that the system decreased or did not alter their seat 

belt use. All but one driver felt the device would be something that parents would want for teenage drivers. Most 

drivers reported that the system was annoying because it 

required them to wear their seat belts when moving the 

vehicle on-site, such as at loading docks, or while parking, 

or on very short trips. Several drivers thought it would 

be useful to have a device that only required seat belt use 

when they traveled over a certain speed. In general, drivers felt the system was acceptable for long trips.

Conclusions 

There was a clear increase in seat belt use—an average 

of 20 percentage points—when the gearshift interlock 

was active for both groups of commercial drivers. Further, drivers who buckled during the intervention period 

were no more likely to remove their seat belts than those 

who buckled during the first baseline. The range of effects 

varied across drivers and across the treatment periods. 

Drivers’ seat belt usage ranged from no response during treatment, to dramatic increases during the treatment 

period only, to maintenance of the change after the gearshift delay was inactivated. 

All but one driver felt the device would be useful to increase 

the seat belt use of teenage drivers. Teen drivers may be an 

appealing target population for this technology, as this population buckles less frequently and crashes more often than 

older drivers. Parents may view such a system as an attractive means of ensuring their children are buckled. Some 

States’ graduated driver licensing laws have consequences 

for teen drivers who drive unbuckled during the initial 

licensure phases, but these laws are difficult to enforce. 

Vehicle fleet owners may also favor a gearshift delay to 

ensure a higher degree of employee compliance with their 

companies’ seat belt use policies. Many fleet owners realize that injury reductions result from increased compliance 

with seat belt policies. This study indicates that the gearshift delay increased such compliance and was acceptable. 

The technology may also have potential in combination 

with current “enhanced” visual and auditory seat belt 

reminders, which have been linked with a significant 

increase in seat belt use (NHTSA, 2007). 

How to Order

Download a copy of Pilot Tests of a Seat Belt Gearshift Delay 

on the Belt Use of Commercial Fleet Drivers (49 pages) from 

www.nhtsa.gov or write to the Office of Behavioral Safety 

Research, NHTSA, NTI-130, 1200 New Jersey Avenue SE., 

Washington, DC 20590, fax 202-366-7394.

Reference: NHTSA. (2007). The Effectiveness of Enhanced 

Seat Belt Reminder Systems. DOT HS 810 844. Washington, 

DC: National Highway Traffic Safety Administration.