9
8
7
6
5
4
3
2
1
0
0-3 Weeks
3-6 Weeks
6-9 Weeks
9-12 Weeks
>12 Weeks
Length of Seasonal Load Restriction
Figure 5. Length of time over which load restrictions are posted.
the wide range of length of time during which
pavement distress are observed, a few states are
load restrictions are in effect (Fig. 5). Some roads
taking a progressive approach to the problem of
are restricted for as long as a third of a year.
thaw weakening, and have researched, or are cur-
Generally, the longer the load restrictions are in
rently researching, relationships among pavement
place, the more complaints were received from
stiffness and other parameters. The USFS is cur-
loggers and contractors. Table 2 lists typical DOT
rently evaluating correlations between pavement
responses regarding user feedback.
stiffness and soil moisture in search of a reliable,
While some states annually post load restrictions
cost-effective method for determining when to sus-
immediately after the first signs of springtime
pend or commence timber hauling (Kestler et al.
1997). It is believed that permanently installed time
domain reflectometry (TDR) and radio frequency
(RF) soil moisture sensors, correlated with strength
recovery, strategically located throughout the for-
est road network will provide this affordable
Table 2. Road user feedback to DOTs and USFS
solution.
on spring thaw load restrictions.
Restricting the flow of goods makes shipping inconve-
SUMMARY
nient.
Some routes too restrictive; length of time too long.
Numerous complaints from contractors and loggers.
Low volume roads subjected to seasonal freez-
"Don't post my road."
ing are highly susceptible to damage from traffic
Haulers want restrictions lifted as soon as possible and
during spring thaw. Although reduced tire pres-
more frequent FWD testing done in these areas.
sure technology is currently being evaluated as a
DOT met with trucking industry association, and they have
jointly funded research on load restrictions.
method for minimizing traffic-induced road dam-
Using quantitative methods for shutting down roads but
age during thaw-weakened periods, at this time
using subjective and arbitrary methods for determining
the most widely accepted and effective practice is
when to reopen roads.
to limit or prohibit heavy loads.
6
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