Effects of road and vehicle conditions, visual warning signs, direction of turns, night time, and skill on automobile driver performance are studied in several experiments. Considered criteria are variability in speed and acceleration

Howard, J. M.

Myers, W. D.

Ritchie, M. L.

English

NASA Technical Reports Server

27. Some Interactions Among Driver, Vehicle, and 
Roadway Variables in Normal Driving 
MALCOLM L. RITCHIE, JOHN M. HOWARD, AND W. DAVID MYERS 
Wright State University 
At the Fourth Annual Manual (ref. 1) I 
reported on a study of driving behavior in which 
we had related lateral acceleration in curves to 
the forward velocity. We plotted the data for 50 
subjects, each of which drove a course containing 
227 identifible curves. The relationship which was 
obtained was 
g = P -0.068(; - 1) 
where g is the lateral acceleration in gravitational 
units, P is a constant for an individual but varia- 
ble between individuals (90 percent of the P 
values were between 0.33 and 0.19 g) and V is 
the forward velocity in miles per hr between 20 
and 60. Since then we have gathered more data, 
have read some interesting reports by others, and 
have thought more about the problem. In  this 
report I will discuss all three developments. 
In  the January 1971 issue of Sports Car Graphic 
there is an article entitled, “World’s Most Ad- 
vanced Race-Driving School” (ref. 2). At this 
school aspiring drivers drove an instrumented car 
which allowed them to study their individual 
performance. The instrumentation produced a 
recording of lateral acceleration and forward 
velocity. The results for the aspiring drivers were 
compared with those for Mark Donahue in an 
effort to discover why Donahue could beat them 
through the course. 
The velocity and lateral acceleration data for 
Mark Donahue were presented in such a way 
that an equation could be derived to express the 
relationship between g and v for those curves in 
which he had a free choice of speed. For Mark 
Donahue the expression is 
g = 1.25 (2) 
No velocity term is in the expression because the 
lateral acceleration did not vary with velocity. 
The car would stay on the road at  1.25 g and 
apparently Donahue’s technique for each curve 
was to achieve and hold that speed which pro- 
duced 1.25 g. 
We may assume that the vehicle used by Mark 
Donahue would lose adhesion at a g value slightly 
higher than 1.25. It is estimated that the Buick 
station wagon which was used in all our experi- 
ments will lose adhesion at about 0.67 g. Where 
Mark Donahue stayed at  something like 98 per- 
cent of breakaway g at all speeds, our ninetieth 
percentile driver achieved 50 percent of break- 
away g at 20 mph, and eased off to about 30 
percent at  60 mph. 
We have become a little more ambitious and 
would like to be able to account for vehicle and 
roadway variables in addition to personal varia- 
bles. We can expand equation (1) as follows: 
g = (Pl,PZ . . . Pn)(Vl,V2 * a v,) 
where PI, P2 etc., are the family of personal 
variables, VI, v 2  etc. are the family of vehicle 
variables, and R ,  Rz,  etc. are the family of road- 
way and environmental variable. We have begun 
to consider which variables in each family account 
for most of the variance. 
In the first study of this series (ref. 3) we found 
that men drove faster and pulled more lateral g’s 
than women. Partially completed analyses sug- 
gest that most of this difference may be due to 
the fact that men drive more miles per year than 
women. In  addition to miles per year we have 
some data on driver’s age, number of years driving, 
219 
https://ntrs.nasa.gov/search.jsp?R=19730001404 2020-03-17T07:19:34+00:00Z
220 SEVENTH CONFERENCE ON MANUAL CONTROL 
and hand dominance. We have found no signifi- 
cance to age and number of years driving. Our 
left-handed drivers drove faster than right 
handed, but the number is too small to be con- 
clusive. In  observing our subjects it appeared 
that there was a relatively large variability due 
to level of aspiration. Some subjects appeared 
quite in awe of the experimenter, while others 
appeared to be making a game of trying to toss 
the recorder in his lap. We plan an experiment 
soon in which we hope to  measure the influence 
of the subjects' understanding of what he is try- 
ing to do. 
In the original experiment all the subjects were 
run in the same vehicle, a 1962 Buick Invicta 
station wagon with power steering and brakes. 
Experimental controls were applied to insure that 
no vehicle variables entered into the experiment. 
Since the original study we have run 60 more 
subjects (making 110 total) in the same car on 
the same 110 mile course over Ohio state high- 
ways. Fifteen of these were run with the tire 
pressure lowered to 21 Ib cold (from the standard 
29). Another 15 subjects were run with the speed- 
ometer covered. The same Buick station wagon 
was used for these runs also. Low tire pressure 
was used as a simple way to get a change in the 
vehicle's dynamic characteristics. The covered 
speedometer eliminated some of the information 
which the machine normally provides the driver. 
Fifteen more subjects were run through the course 
at night, and a final 15 subjects acted as a con- 
trol group, repeating the conditions of the first 
experiment. 
The results of these four conditions are shown 
in figures 1 and 2. The data points for each curve 
are grouped by the mean velocity for that curve 
in the first experiment. Figure 1 shows the re- 
corded speed plotted against the reference speed 
for each curve. It will be seen that the speeds for 
the night and the control condition are indis- 
tinquishable statistically from each other, but 
both may be distinquished from the low tires 
and the no speedometer condition, which are in 
turn indistinquishable from each other. The gen- 
eral statement is that the group with low tires 
and the group with no speedometer drove faster 
than the control group, but the night group did 
not drive faster than the control. 
Figure 2 shows lateral acceleration plotted 
Xa.0 13.106 18.856 22.806 27.131 31.369 36.031 19.056 bI.756 14.331 
2 M l g h i  I . D .  1.3b4 1.027 2.667 3.611 3.662 b.198 6.461 k.2110 4.143 
3 l w d o -  *.an 15.753 20.05) 16.187 30.060 35.510 39.353 b3.407 16.180 49.293 
n.l.r 5 . 0 .  2.488 5.9b8 5.021 1.170 4 . 2 5 2  3.936 ).l69 5.169 5 . I l l  
, ;zs, yr t 6 . W  %%.Is7 1b.607 S . Z h 0  33.3,) 37.993 *1.610 15.767 l9.367 2.163 5.181 3.137 3.859 I.5Ob b.971 5.142 5.281 5.966 
5 csntrol 6e.n 12.619 1 8 . 0 1  22.k21 16.86) 32.036 36.1D7 40.171 11.450 (6.714 
I.@. 2.612 3.152 3. l t t  h.013 3.919 1.876 1.421 11.125 1.607 
FIQURE 1.-Comparative speed in turns for night (2), 
no speedometer (3, and low tires (4). 
against the reference speed for each curve. It will 
be seen that the night group produced lower 
accelerations than the low tires, no speedometer, 
and the control groups; these latter three being 
statistically indistinquishable. 
How is it possible that the control group drove 
no faster than the night group but still produced 
higher lateral accelerations? When the data from 
the two-channel Brush recorder were read, the 
acceleration value read was the peak acceleration 
produced in a given curve. The velocity was then 
read at  that point. If the control group drivers 
systematically jerked the wheel to a greater 
degree than the night group, thus producing 
greater spikes on the lateral acceleration trace, 
the result would be as observed in the two figures. 
In the report we gave at  the 4th Annual Manual 
(ref. 1) we showed figure 3, which js a plot of the 
recorded speed as a function of the speed values 
of advisory signs. Our subjects drove faster than 
INTERACTIONS AMONG DRIVER, VEHICLE, AND ROADWAY VARIABLES 22 1 
504 
I 
454 
I 
404 
I 
354 
I 
304 
I 
254 
I 
I 
I5 4 
L 
2oJ 
I5 ' 1 0  25 ' 3 0  '35 ' 4 0  45 ' 5 0  Tmls 
A.illsvrf S I P  sped  
-4 Man 21.950 sllw 32381 37.900 42.177 42.lW 44.425 49.623 JP.W 
S P ~  SD 1.900 5101 ZMO 2.036 2.596 mi 4.1w 3.w 7.919 
N 4  10 6 6 I3 11 12 6 68 
F - 5.1144 DF - 7/64 
FIGURE 3.-Actual speed in curves in 
relation to advisory sign speed. 
.m 4 
\With Advlsory Speed 
.m 4 
I 
1 
,180 4 
/- .'*: Without Advisory Speed  
.I40  4 
I 
,1104 
I 
-10 '10-25 '25J) '3035 ' 3 5 4  ' (w ' 4 5 - 4 )  , 5 0 4 5  T&I 
Fomrrrd vdosiy In H l r s  Per h r  
W B  Man 0.263 0.268 0.257 0.222 0.224 0.185 0.161 0.169 0.m 
Advlmq SO 0. 0.061 O.MI 0.W 0.037 0.053 0,043 0.W 0.059 
S p d  N 1 4 6 IO 12 19 13 3 68 
W i l h a n h k w  0.264 0.234 4153 0.165 0.105 0.145 0.130 1.1% 0.1% 
Advisory SD 0.059 0.059 0.043 0.021 0.045 0.035 0.039 0.041 0.059 
S p e d  N 8 2 5 6 8 9 22 34 94 
B h a n  F 0.0333 0.265 3.W 6.319 2.445 4.W 4.726 3.156 2&X6 
Gro~pr DF 1 P  1/4 l/p 1/14 1/16 1/26 1/33 1/35 I/IM 
F I ~ U R E  4.-Effect of the presence of advisory 
speed sign upon choice of speed in curves. 
the signs reading below 40, but did not drive 
faster than advisories of 45 and 50. Figure 4 
shows the lateral acceleration for those curves 
with advisories and for the curves without 
advisories. We have looked at the individual 
curves with advisories in relation to their advisory 
speeds. Mean values for our 110 subjects show 
considerable variability in speed and acceleration 
with a given advisory speed. Using these data we 
are negotiating with the Ohio Department of 
Highways a contract to revise considerably the 
methods by which advisories are assigned. 
Selecting 162 curves which gave the drivers a 
free choice of speeds, we had 79 with a curve 
sign and 83 without. Figure 5 shows the plot of 
lateral acceleration for these two conditions. 
(Note that all 68 curves with advisory signs in 
figure 4 are among the 79 curves in figure 5 
wilhout  an am aim aim 0.165 0 . 1 5 ~  0.110 a m  aiu O . I S ~  
Slpn ID 0.W 0. Mu 0.021 0.W 0.139 0.042 0 . M  0 . m  
N 7  1 5  6 7 7 V D  81 
FIGURE 5.-Effect of the presence of a curve 
sign on the choice of speed in curves. 
Rirhl hkw 0.276 0.317 0.247 0.109 0.226 0.188 0.151 0.145 0.188 
T U ~ ~ S  so am o m  o.om o.m 0.038 om 0.w o.oa 0.- 
N 5  3 5 5 12 13 19 ?3 85 
Left b n  0.249 0.198 0.212 0.197 0.191 0.159 0.131 0.102 0.162 
Turns SD 01161 O m 0  0.054 0.033 0.M 0.037 0.034 0.033 0.W 
BoWan F 0.477 23.553 0.810 0.192 3.878 2.45 2.020 12.381 7.086 
N 4  3 6 I I  8 15 16 14 77 
G~~~ OF i/n i/4 i/p 1/14 1/18 1/26 1/33 I/JS i/im 
FIGURE 6.-Effect of the direction of turn 
on the choice of speed in curves. 
which had curve signs. No curve had an advisory 
without a curve sign, but 11 had curve signs and 
no advisory.) 
These 162 curves consisted of 85 right turns 
and 77 left turns. The speed versus lateral accel- 
eration data for right versus left are shown in 
figure 6. The difference is reliable because the two 
curves do not overlap. It is a small difference, 
however, and is about the same order as the 
limits of the relatively simple instrumentation 
system. Therefore, these data must be considered 
as being subject to revision. 
REFERENCES 
1. RITCHIE, MALCOLM L.: Some Relations Between 
Visual and Kinesthetic Displays in Normal Driving. 
Proceedings of the Fourth Annual NASA-University 
222 SEVENTH CONFERENCE ON MANUAL CONTROL 
Conference on Manual Control, Univ. of Michigan 
(Ann Arbor, Mich.), Mar. 21-23, 1968, pp. 459-463. 
2. VAN VALKENBURG, PAUL: World’s Most Advanced 
Race-Driving School. Sports Car Graphic, Jan. 1971, 
pp. 58-61, 67. 
3. RITCHIE, MALCOLM L.; McCoy, WILLIAM K.; ADN 
WELDE, WILLIAM L.: A Study of the Relationship 
Between Forward Velocity and Lateral Acceleration 
in Curves During Normal Driving. Human Factors, 
vol. 10, no. 3, 1968, pp. 255-258. 


Some interactions among driver, vehicle, and roadway variables in normal driving

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