The Rural Highway Driver Warning System (RHDWS) is designed for preventing run-off-road (ROR) collisions on curvy rural highways. In this system, three types of warnings were provided to the drivers: 1) lane departure warning, 2) curve ahead warning, and 3) speed limit warning. With the help of such systems, drivers would have enough time to adjust their speeds and driving behaviors to respond to the unexpected roadway conditions ahead, such as sharp curves.

Methodology

The system was tested by conducting driving simulator experiments. For the RHDWS, two driving scenarios were designed and programmed in the driving simulator environment: (1) the baseline scenario (normal situation: driving a vehicle on a two-lane, rural highway without any warning system, and (2) the study scenario: driving a vehicle with the designed warning system on the same rural highway.

After conducting the driving simulation experiments, the participants' driving performance under different driving scenarios were evaluated based on the outputs of the driving test. In this study, the following measures of effectiveness (MOE) were derived for analyzing driving performance.

• Number of Critical Events.
• Number of ROR Events.
• Maximum Deceleration.
• Speed Conformity Percentage (percentage of time that the subject vehicle is traveling at a speed that is lower than the speed limit).

After the experiments, the participants were also surveyed to obtain their opinions of the driving warning system.

Results

A statistical method for comparing the means of two groups of related samples (paired t test) was used to compare the MOEs from both driving scenarios. The results were:

• The average number of critical events in the study scenario was significantly less than in baseline scenario (t = 1.918, P = 0.065). This result indicates that the driver warning system can significantly reduce the critical events by as much as approximately 21 percent.
• The average number of ROR events was drastically decreased in the study scenario compared with that in the baseline scenario (t = 5.248, P = 0.000). This shows that the driver warning system has improved the driver's safety by decreasing the ROR crashes by approximately 71 percent.
• The difference between maximum deceleration in the baseline scenario and in the study scenario was also very significant (t = -2.124, P = 0.042). The results show that the system decreased the maximum deceleration by approximately 70 percent, which indicates that the driver warning system contributed to smoother driving on the curvy highway, thereby improving safety on such a roadway.

Statistical analysis results also proved that the speed limit conformity percentage of the study scenario is significantly higher than that in the baseline scenario (t = -10.891, P = 0.000) which also indicates that the driver warning system can improve the driver's safety by preventing speeding.

The survey taken by subjects after participating in the driving simulator experiment had them score the three warning functions according to their effectiveness in preventing ROR crashes (where 5= “Extremely Helpful” and 1=“Not Helpful At All”). On average, the results were:

• Curve ahead warning = 4.3
• Lane departure warning = 3.93
• Speed limit warning were =3.97.

These results indicate that the drivers felt that the curve ahead warning was the most useful in preventing ROR crashes.

Overall, the experimental results show that this system can significantly reduce ROR collisions in a rural highway environment. In addition, according to the survey of the tested drivers, the system is easy for the driver to use and helpful to them in safely negotiating a curvy rural highway.