Because this is an empirically based model, and
Table 3. Internal motion resistance coefficients.
because mobility is a continuing area of interest
to the U.S. Army, improvements and expansion
of the model are to be expected. In the process of
preparing this report a number of areas needing
Superhighways and primary roads and ice
improvement were identified. For mobility/traf-
ficability analysis over snow-covered areas, the fol-
lowing need further research: motion resistance
Trails and cross country (Pfg* ≥ 4.0)
in shallow snow, deep snow trafficability, and snow
Trails and cross country (Pfg < 4.0)
over a soft soil with large sinkage values. For op-
erations on ice the effects of temperature and trac-
* Pfg = w/(nbr), in psi, where, w is the weight on an axle, n is the
tion aids needs further study. In freezing/thawing
number of wheels on an axle, b is the wheel width and r is the
soils further tests with heavy vehicles are required,
the types of soils investigated need to be expanded,
and tracked vehicles need to be evaluated.
The main effect of slopes is the redistribution
of the force of gravity on the vehicle body forces
(Yong et al. 1984). This redistribution is seen as an
Abele, G. (1990) Snow roads and runways. USA
additional resistance term due to gravity and a re-
Cold Regions Research and Engineering Labora-
duction of the normal load on each wheel or track
tory, Monograph 90-3.
assembly. Richmond (1993) examined this ap-
Ahlvin, R. and P. Haley (1992) NATO reference
proach using the traction and resistance equations
mobility model edition II, User 's guide, Volume I
for snow presented earlier and obtained good
(NRMM II). USA Waterways Experiment Station,
results when compared with go/no-go tests on
Technical Report GL-92-19.
slopes. The effect of slopes on traction is imple-
Blaisdell, G.L. (1984) Winter traction aids for
mented by multiplying the normal load on a wheel
wheeled vehicles. In Proceedings of the 1984 Army
or track by the cosine of the slope angle. The effect
Science Conference, 19-21 June 1984, West Point, New
on resistance is implemented by adding a resistance
term due to gravity, which is equal to the gross ve-
Blaisdell, G.L. and S. Borland (1992) Braking trac-
hicle weight times the sine of the slope angle, to
tion on sanded ice at low slip rates. Report prepared
for Federal Aviation Administration, Washing-
ton D.C., by USA Cold Regions Research and En-
Blaisdell, G.L., P.W . Richmond, S.A. Shoop, C.
Green and R.G. Alger (1990) Wheels and tracks
in snow: Validation study of the CRREL shallow
The algorithms, rationale and data sources for
snow mobility model. USA Cold Regions Research
what we call the Cold Regions Mobility Model
and Engineering Laboratory, CRREL Report 90-9.
have been presented. These algorithms are pri-
Clark, S.K. (1982) Mechanics of pneumatic tires.
marily empirical in nature and rely on relatively
U.S. Department of Transportation. Washington,
simple terrain measurements. Appendix A con-
D.C.: U.S. Government Printing Office.
tains a stand-alone FORTRAN code of the Cold
Falls, T.C., C.D. Butler, B.T. Webb, J.L. Williamson
Regions Mobility Model (CRM-1.F); sample data
and A. Chase (1989) A User's Guide for CAMMS
files and output are presented.
We did not address the accuracy of the algo-
MacFarlane, I.C. (1968) Strength and deformation
rithms in this report; the reports in which these
tests on frozen peat. In Proceedings of the Third In-
algorithms were initially developed discuss this
ternational Peat Congress, Quebec, Canada, August
issue somewhat. Future work will examine im-
1823, 1968, p. 143149.
provements in the algorithms and the overall ac-
Niemi, E.W . and R. Bayer (1970) Analytical pre-
curacy with regard to speed made good and go/
diction of vehicle mobility on muskeg. U.S. Army
Tank Automotive Command, Warren, Michigan,