1

To Alert or Assist: Comparing 

Effects of Different Lateral 

Support Systems on 

Lane-Keeping 

FHWA Publication No.: FHWA-HRT-20-068

FHWA Contact: Brian Philips, HRDS-30, ORCID: 0000-0002-

8426-0867, (202) 493-3468, brian.philips@dot.gov

OBJECTIVE

This TechBrief describes an experiment examining the effect of lateral 

support systems on driving behavior and user acceptance of lateral 

support systems. The research team used a driving simulator to compare 

lane-keeping behavior when drivers were controlling the vehicle 

without lateral assistance (i.e., manual control) or were assisted by 

lane-departure warning (LDW) or lane-keeping assist (LKA) systems. 

The goal of the study was to assess the effect of each type of lateral 

support system on drivers’ lane-keeping ability in different situations 

and examine driver acceptance of lateral support technology.

INTRODUCTION

Road-departure crashes, in which a vehicle inadvertently drifts off 

the road, are among the most severe types of crashes, making up 

37 percent of highway fatalities.(1)

 Lateral support systems have 

the potential to reduce road-departure crashes by decreasing the 

probability that a vehicle will leave its intended travel lane. Two lateral 

support systems on the market are LDW and LKA. LDW systems issue 

a visual, audible, or haptic warning to alert the driver that the vehicle 

has crossed a lane boundary. LKA systems actively move the vehicle 

back into its lane by either applying steering torque or light differential 

braking. 

Both types of lateral support systems have potential safety benefits. 

LDWs have been found to improve lane-keeping.(2,3) In the event of a 

lane departure, drivers can directly respond to LDW alerts to guide 

their vehicle back into their lane. Additionally, the presence of an LDW 

system has been found to increase drivers’ lane-keeping vigilance 

and turn-signal use.(1,3) However, warning systems require a driver 

to recognize and respond correctly to an alert, which creates the 

possibility of drivers sometimes failing to notice an alert, particularly if 

the driver is distracted.(4) 

LKA systems eliminate the possibility that a driver may fail to correctly 

respond to a lane departure by taking corrective action when a lane 

departure occurs. This action also reduces the risk that a driver will 

overcorrect in response to an LDW. Nevertheless, some researchers 

have expressed concern over potential human factors issues related to 

LKA. Pohl and Ekmark found that drivers who were naïve about an LKA 

system had difficulty understanding it.(5)

 Beruscha et al. point out that 

Research, Development, and 

Technology

Turner-Fairbank Highway 

Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

https://highways.dot.gov/research

TECHBRIEF
2

if a driver misinterprets a change in torque felt on the 

steering wheel as a wind gust or vehicle malfunction, 

then the driver may steer in the opposite direction of the 

automatic corrective action, overriding the potentially 

positive impact of the system.(4)

 Other authors have 

expressed concern that the automation provided by LKA 

could lead to a degradation in lane-keeping ability that 

would negatively affect driver safety in the event of a 

system failure.(2,6,7)

Both LDW and LKA systems are designed to help keep 

the vehicle in its intended travel lane and prevent roaddeparture crashes. Meeting these goals requires a 

positive interaction between the lateral support system 

and the driver to promote safer driving behavior in 

different situations. First, a lateral support system should 

increase the amount of time that a driver spends in their 

lane relative to manual driving. If a driver does leave 

their lane, an effective lateral support system should 

minimize the time the vehicle spends outside of the lane 

either by alerting the driver about the lane departure or 

automatically correcting the lane departure. While less 

common, it is likely that drivers will also occasionally 

encounter situations in which a lateral support device 

issues an unneeded alert or lane correction. For 

example, when entering a work zone or maneuvering 

around obstacles in the roadway, drivers may need 

to cross lane boundaries, which will activate a lateral 

support system. Drivers need to ignore an LDW alert or 

override an LKA correction with sufficient ease during 

these false-positive situations to prevent a potentially 

dangerous driver–system interaction. Finally, drivers 

may encounter situations in which a lateral support 

system does not issue a needed alert or correction. 

Lateral support systems use sensors to detect lane lines 

and may not function correctly on roadways on which 

lane lines are faded, absent, or obscured. Additionally, 

lateral support systems may fail in situations where 

sensors are obscured by debris or weather. Drivers 

need to be able to maintain adequate lane-keeping in 

the event of an unexpected system failure. 

The current study compared lane-keeping behavior 

when drivers drove without lateral assistance, with 

LDW, or with LKA. The goals of the study were to 

assess the effect of each type of lateral support system 

on lane-keeping ability during conditions in which a 

driver unintentionally leaves their travel lane, assess 

how drivers respond to lateral support systems triggered 

in response to an intended lane departure, and 

determine whether drivers respond appropriately to 

lane departures following an unexpected lateral support 

system failure. User acceptance of each system was 

also examined.

RESEARCH

Seventy-two licensed drivers from the Washington,DC, 

metropolitan area participated in the study. The study 

was conducted in a fixed-base driving simulator 

equipped with LDW and LKA systems. When either 

lateral support system was engaged, a green icon 

depicting a car crossing a lane line appeared in the 

central console (figure 1). The icon turned yellow when 

the vehicle crossed a lane line without a turn signal. The 

icon was not visible when the lateral support system 

was not engaged. Haptic LDW alerts took the form of 

lateralized vibrations in the driver’s seat. LKA corrections 

took the form of torque applied to the steering wheel 

that moved the vehicle back toward the center of the 

lane. The torque could be felt and overridden by the 

participant. One-third of participants drove with LDW, 

one-third drove with LKA, and one-third drove without 

either lateral support system.

All participants drove on a 22-mile-long undivided 

two-lane road in a semirural setting. Figure 2 shows 

the simulated route participants drove. Light traffic in 

the opposing lane encouraged participants to remain 

in their lane, but traffic was not present during any 

event intended to induce a lane departure. Simulated 

wind gusts occurred at eight points during the drive 

to induce lane departures. Wind gusts were designed 

to push the participant’s vehicle in a predetermined 

direction across a lane boundary. An audio recording 

of wind played as part of each wind gust. In the LDW 

condition, crossing a lane boundary triggered a haptic 

alert. In the LKA condition, crossing the lane boundary 

triggered a steering correction. No alert or steering 

correction occurred in the manual-driving condition 

when crossing the lane boundary. In addition to the 

eight simulated wind gusts, faux wind gusts occurred 

seven times during the drive to prevent participants from 

anticipating wind gusts. During a faux wind gust, the 

Figure 1. Illustration. Lateral support icon.

Source: FHWA.
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wind sound played but lateral force was not applied 

to the vehicle. Between the fourth and fifth wind gusts, 

participants encountered an obstacle in their travel 

lane. The obstacle, a metal desk, was large enough that 

participants had to depart the lane to avoid it. After the 

fifth wind gust, the lateral support system unexpectedly 

disengaged; the lateral support icon went dark, and 

lane departures no longer triggered LDW alerts or LKA 

corrections. Participants experienced three additional 

wind gusts before reaching the end of the scenario. 

Following the drive, all participants completed the Van 

der Laan questionnaire.(8)

 This nine-item questionnaire 

provides separate measures of the usefulness and user 

satisfaction with new in-vehicle technologies.

RESULTS

Comparison of lane-keeping across lateral support 

conditions found that drivers in the LDW condition 

tended to have better lane-keeping than those in the 

LKA or manual conditions (table 1). Drivers in the 

LDW condition spent less of the drive outside of their 

lane, returned to their lane more quickly when a lane 

departure occurred, and held a more constant position 

while in their lane. Drivers’ lane-keeping in the LKA 

Figure 2. Illustration. Lateral support icon.

Source: FHWA.

Table 1. Driving performance as a function of condition.

Condition

Mean of Drive Spent 

Outside Lane 

(%)

Mean Lane Departure 

Duration

(s)

Mean Lane Position 

Variability

(ft)

Mean Speed

(mi/h)

LDW 1.51 1.21 0.99 44.9

LKA 3.27 1.78 1.12 45.19

Manual driving 3.02 2.86 1.17 43.14
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condition did not match those in the LDW condition, but 

the group did show reduced lane-departure durations 

relative to those in the manual driving condition. 

Participants in the manual driving condition also showed 

reduced travel speeds relative to those in the LDW 

or LKA conditions, suggesting that the difference in 

lane-keeping ability was not due to a lane-keeping/

speed tradeoff. In fact, participants in the LKA condition 

maintained similar levels of lane-keeping to participants 

in the manual condition while driving more quickly, 

suggesting that LKA improved drivers’ lane-keeping.

During the drive, participants were required to 

maneuver around an obstacle in their travel lane 

(figure 3). Drivers needed to use the turn signal prior to 

exiting the travel lane to avoid receiving an alert from 

the LDW system or steering correction from the LKA 

system. Most participants (i.e., 62.5 percent) used the 

turn signal prior to exiting the travel lane. Turn-signal 

use did not vary by lateral support condition, and every 

participant successfully avoided the obstacle. 

When maneuvering around the obstacle, participants 

were free to choose their path. They could venture far 

into the opposing lane or remain close to the obstacle. 

This choice was reflected in the distance traveled during 

their lane departure. Participants in the LDW and LKA 

conditions did not travel as far (mean = 446.5 ft and 

mean = 527.9 ft, respectively) when maneuvering 

around the obstacle compared to those in the manual 

driving condition (mean = 599.3 ft). 

Lane-keeping and speed were also measured when the 

lateral support system unexpectedly failed. Participants 

who used LDW or LKA during the first section of the 

drive had similar lane-keeping performance when those 

systems were disabled compared to participants who 

drove manually. 

Following the drive, all participants completed the 

Van der Laan questionnaire, which provides separate 

measures of the usefulness and user satisfaction with 

new in-vehicle technologies. Scores for each measure 

range from +2 to −2, with positive scores indicating 

a positive view of the system and negative scores 

indicating a negative view. Results indicated that 

participants had a positive impression of both lateral 

support systems. Participants gave the LDW and LKA 

systems positive ratings for both user satisfaction and 

usefulness (mean = 1.11 and mean = 1.3, respectively). 

The systems were rated positively not only by 

participants who experienced the lateral support system 

during the experiment but also by participants who 

selected ratings based on their expectations about the 

systems after reading information about each one prior 

to completing the questionnaire. 

Figure 3. Screenshot. Obstacle encountered during the drive.

Source: FHWA.
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Most participants (i.e., 54 percent) indicated that they 

were very unfamiliar with lateral support technologies 

prior to the experiment. However, the more familiar 

a participant indicated they were with LDW or LKA 

systems, the higher they rated its usefulness and their 

satisfaction with it (figure 4).

CONCLUSIONS

This study assessed the influences of lateral support 

systems on lane-keeping. Participants were divided 

into three conditions: LDW, LKA, and manual driving. 

Simulated wind gusts were used to induce lane 

departures throughout the drive. Participants in the 

LDW condition spent less of the drive outside of their 

lane, returned to their lane more quickly when a lane 

departure occurred, and held a more constant position 

while in their lane. Participants in the LKA condition did 

not match those in the LDW condition, but the group 

showed reduced lane-departure durations relative to 

those in the manual driving condition. Participants in the 

manual driving condition also showed reduced travel 

speeds relative to those in the LDW or LKA conditions, 

suggesting that the difference in lane-keeping was 

not due to a lane-keeping/speed tradeoff. In fact, 

participants in the LKA condition maintained similar 

levels of lane-keeping compared to participants in the 

manual condition while driving more quickly, suggesting 

that LKA improved drivers’ lane-keeping ability. The 

findings speak to the potential usefulness of lateral 

support systems for reducing lane departures.

One concern associated with lateral support systems 

is whether drivers react appropriately during situations 

in which the lateral support system activates when 

a driver intends to leave their lane. Will drivers be 

able to ignore the LDW alert or override the LKA 

correction with sufficient ease to prevent a potentially 

dangerous system–driver interaction if a lateral support 

system issues an unwarranted or unneeded alert or 

lane correction? To assess this research question, the 

current study included an unexpected obstacle in 

the participants’ travel lane. The size of the obstacle 

required participants to cross their lane boundary 

to avoid it. All participants successfully avoided the 

obstacle without issue. The results indicate that the LDW 

and LKA systems did not create a dangerous situation 

when drivers had to change lanes suddenly during 

an avoidance maneuver. Participants who did not use 

their turn signal prior to exiting their lane experienced 

an LDW alert or an LKA correction when making this 

avoidance maneuver. These participants chose a path 

that returned them to their lane more quickly than those 

who used their turn signal and thus did not trigger the 

lateral support system. The warnings and corrections 

issued by the lateral support systems may have 

reminded participants of the potential dangers of driving 

in the opposing lane of traffic, such that they remained 

in the opposing lane for less time than those in the 

manual-driving condition; however, additional research 

is needed to verify this hypothesis.

Figure 4. Graph. Usefulness and satisfaction ratings as a function of familiarity with the lateral support system 

being rated.

Source: FHWA.
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Another potential concern associated with lateral 

support systems is drivers becoming so reliant on 

the systems that their lane-keeping ability may be 

compromised if the lateral support system unexpectedly 

fails.(2,6,7)

 Lateral support systems currently on the market 

depend on sensors that detect lane lines and are unable 

to function correctly on roadways on which lane lines 

are faded or absent or in situations where lane lines or 

sensors are obscured by debris or inclement weather. 

One issue of interest is whether drivers who use lateral 

support systems can maintain adequate lane-keeping 

in the event of an unexpected system failure. To assess 

this issue, lateral support systems stopped functioning 

during the last section of the drive. Participants did not 

show any reduction in lane-keeping ability because of 

unexpected lateral support system failure. These results 

are consistent with the findings of Petermeijer et al., who 

found that drivers who are not distracted quickly recover 

lane-keeping after lateral support failure.(9)

Finally, for lateral support system to be successful, 

drivers need to understand and trust the systems. 

The current study used a questionnaire to assess the 

perceived usefulness of and user satisfaction with the 

LDW and LKA systems. Participants in all conditions 

indicated that they found the systems both useful 

and satisfying to use. Moreover, the more familiar 

participants were with the lateral support system in 

question, the higher their trust in the system. The results 

are consistent with past research indicating that user 

acceptance of vehicle automation increases with 

increased system use.(10)

 The current findings expand 

on previous work by demonstrating that even drivers 

who indicated they were very unfamiliar with the lateral 

support system being tested rated the system positively. 

The results indicate high user acceptance of lateral 

support automation. Overall, the results of the current 

study suggest that lateral support technology is poised 

to improve driver and roadway safety. 

REFERENCES

1. LeBlanc, D., Sayer, J., Winkler, C., Ervin, R., 

Bogard, S., Devonshire, J., Mefford, M., et al. 

(2006). Road Departure Crash Warning System 

Field Operational Test: Methodology and Results, 

The University of Michigan Transportation Research 

Institute, Ann Arbor, MI.

2. Brown, C.M. (2001). “New in-vehicle technologies: 

are lane departure warnings a good thing.” 

Proceeding of the SELF-ACE 2001 Conference–

Ergonomics For Changing Work, Montreal, 

Canada.

3. Rimini-Doering, M., Altmueller, T., Ladstaetter, 

U., and Rossmeier, M. (2005). “Effects of lane 

departure warning on drowsy drivers’ performance 

and state in a simulator.” Proceedings of the Third 

International Driving Symposium on Human Factors 

in Driver Assessment, Training, and Vehicle Design. 

Rockport, ME.

4. Beruscha, F., Augsburg, K., and Manstetten, D. 

(2011). “Haptic warning signals at the steering 

wheel: a literature survey regarding lane departure 

warning systems (short paper).” Haptics-e, The 

Electronic Journal Of Haptic Research, 4(5), 

pp. 1–6, New York, NY.

5. Pohl, J. and Ekmark, J. (2003). “A lane keeping 

assist system for passenger cars-design aspects of 

the user interface.” Proceedings: 18th International 

Technical Conference on the Enhanced Safety Of 

Vehicles, Nagoya, Japan.

6. Kovordányi, R., Ohlsson, K., and Alm, T. (2005). 

“Dynamically deployed support as a potential 

solution to negative behavioral adaptation.” 2005 

Intelligent Vehicles Symposium Proceedings, 1, 

pp. 613–618, Las Vegas, NV.

7. de Winter, J.C.F. and Dodou, D. (2011). “Preparing 

drivers for dangerous situations: A critical reflection 

on continuous shared control.” 2011 IEEE 

International Conference on Systems, Man, and 

Cybernetics, pp. 1050–1056, Anchorage, AK.

8. Van Der Laan, J.D., Heino, A., and De Waard, D. 

(1997). “A simple procedure for the assessment 

of acceptance of advanced transport telematics.” 

Transportation Research Part C: Emerging 

Technologies, 5(1), pp. 1–10. Amsterdam, The 

Netherlands.

9. Petermeijer, S.M., Abbink, D.A., and de Winter, 

J.C.F. (2015). “Should drivers be operating within 

an automation-free bandwidth? Evaluating haptic 

steering support systems with different levels of 

authority.” Human Factors, 57(1), pp. 5–20, 

Washington, DC.

10. Sullivan, J.M., Flannagan, M.J., Pradhan, A.K., and 

Bao, S. (2016). Literature Review of Behavioral 

Adaptations to Advanced Driver Assistance 

Systems, AAA Foundation, Washington, DC.
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 NOVEMBER 2020 FHWA-HRT-20-068

HRDS-30/11-20(WEB)E

Researchers—This study was performed by Starla Weaver (ORCID: 0000-0002-9559-8337) of Leidos. 

Statistical analysis was performed by Tracy Gonzalez (ORCID: 0000-0003-2672-1343) of Leidos. The study 

was conducted under contract number DTFH61-13-D-00024.

Distribution—This TechBrief is being distributed according to a standard distribution.

Availability—This TechBrief may be obtained online at https://highways.dot.gov/research.

Key Words—Lateral support, lane departure warning, lane-keeping assist, driving simulator, driver 

acceptance of technology.

Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation 

(USDOT) in the interest of information exchange. The U.S. Government assumes no liability for the use of the 

information contained in this document. The U.S. Government does not endorse products or manufacturers. 

Trademarks or manufacturers’ names appear in this TechBrief only because they are considered essential to the 

objective of the document.

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