5B-3-6 
time. It was expected that the HISS could be 
used to determine the geometric parameters of 
road such as superelevation, slope, and radius 
of curvature. But in a field test, it is impossible 
to identify exactly the beginning and end of the 
curve in comparison of data determined from 
the HISS with the actual road alignment. 
Therefore, we tried to compare the HISS data 
with the constant reference data by 
conventional method. 
Gradient 
If the inclination of vehicle with respect to the 
road can be neglected, then the superelevation 
is given by roll, while the gradient is given by 
pitch. The road with a constant slope at a 
distance of 150 meters was selected for test 
field. The average gradient of road was 
measured by the total station. Test data were 
recorded after the vehicle has run in the 
INS/Odometer mode for 20 minutes. The 
gradients were obtained by taking a 
movement-average of 50 pitch data are shown 
in Figure 6. This method gives fairly good 
agreement with the reference slope 6.93 % 
taken from the total station. As shown in 
Figure 7, raw pitch angles fluctuated around 
the reference values. This is most likely due to 
vehicle vibration and dynamics. 
0 50 100 150 
Distance (m) 
Figure 6 Gradient of Road 
1 101 201 301 401 501 
Time (20msec) 
Figure 7 Pitch data of HISS 
Radius of Curvature 
The circular curve at a distance of 500 meters 
was selected as test run course. The reference 
radius of curvature was calculated by taking 
three consecutive points from a map with a 
scale of 1:500 and conducting the perpendicular 
bisector of two cords. The average read off from 
map was 496 meters. As shown in Figure 8, 
Radius of curvature R was calculated from 
heading 0 and the cord L by positions between 
a second before and after. Radius of curvature 
determined by this method is shown in Figure 
Figure 8 Calculation of Radius of Curvature 
^ 600 
v 500 
I 400 
> 
= 300 
0 200 
CO 
1 100 
«3 
0 
0 100 200 300 400 500 
Distance (m) 
Figure 9 Radius of Curvature 
Fluctuations in the radius of curvature can be 
read off the figure. The relative accuracy of 
heading is quite good, below 0.05 degree, 
because there is no vibration about azimuth- 
axis. Therefore, it seems to be the personal 
peculiarity of a driver. As a driver usually tends 
to adjust handle in several seconds, periodical 
change of heading appears easily. 
4.4 Continuous Running Test 
The continuous running test was conducted 
through the Tomei Expressway, the 
Metropolitan Expressway and national roads. 
The vehicle traveled on 20 kilometers round- 
trip for about 2 hours. In this route, the traffic 
is very heavy and also there are many tall 
buildings that cover GPS signals. The vehicle