TRAVEL SPEEDS IN THE SUMMER OF 1973
- These are selected from the U.S. Dept. of Transportation, Federal Highway Administration,
"Traffic Speed Trends" Report, HHP-13, dated June 25, 1974. This report contains data
from the last summer before the oil-price-crisis and Federal fettering of speed limits.
As the first paragraph of the Report says:
-
Attached is a copy of the 1974 "Traffic Speed Trends" report based on data collected by
37 States during 1973. The report summarizes data obtained from studies conducted primarily
during the spring and summer seasons and the information, therefore, is comparable to past
reports. However, it does not reflect the reduced speeds at which drivers were traveling
toward the end of the year.
- From "Table 2- Average Speeds of Free-Moving Vehicles and Percentages of Vehicles
Traveling in Excess of Various Speeds on Level, Straight Sections of the Completed
Portions of the Rural Interstate System for 1973", I selected (presumably daylight)
speed data from the states of
- Montana
- (then and now)
reasonable and prudent {link to MT DOT site}
for cars (day; 65-mph night), 65-mph for trucks.
- Ohio
- (then) 70-mph for cars, 55-mph for trucks
- Rhode Island
- the only (then) 60-mph state with speed data from more than one monitoring station
I estimated the 85th percentile speed from the available data.
|
State |
Vehicles |
Average speed |
85th%tile |
over 60mph |
over 65mph |
over 70mph |
over 75mph |
# stations |
|
MT |
All |
67.1mph |
76mph |
73% |
54% |
36% |
19% |
4 |
|
|
Cars |
70.5mph |
78mph |
85% |
68% |
48% |
26% |
|
|
|
Trucks |
60.9mph |
70mph |
50% |
26% |
14% |
5% |
|
|
OH |
All |
63.8mph |
72mph |
71% |
47% |
22% |
4% |
6 |
|
|
Cars |
66.6mph |
72mph |
89% |
63% |
31% |
6% |
|
|
|
Trucks |
56.7mph |
62mph |
26% |
4% |
0% |
0% |
|
|
RI |
All |
62.2mph |
69mph |
52% |
33% |
10% |
5% |
2 |
|
|
Cars |
62.7mph |
69mph |
54% |
35% |
11% |
6% |
|
|
|
Trucks |
59.9mph |
63mph |
42% |
22% |
2% |
1% |
|
From a practical stand point, the differences in average travel speeds between
60-mph, 70-mph, and no speed limit appear pretty small. The so-called "speed variance"
ranged from 7-mph in Rhode Island to 9-mph in Montana.
From this data set, the largest variance is for trucks in Montana; however, I'd attribute
that more to truckers exploiting the low-volume of traffic there, rather than the speed limit,
because Montana truck speeds were even higher than in states allowing trucks 70-mph or 75-mph
limits (data in Table 2, but not shown above).
- TECHNICAL FOOTNOTE on "speed variance"
- Statistically, subtracting the 85th%tile from the mean average
approximates the standard deviation (SD) of a normal distribution.
The variance is the square of the SD. However, the traffic engineering community
often refers to as the SD of speeds as the "speed variance." Those in the
Quality profession recognize the SD by its symbol, "sigma."
Back to the Ohio NMA rootpage.