dozen GPS/AVL equipped maintenance vehicles. There are some technical issues with
these data that are discussed in the next section, but overall, these data were very valuable
in understanding the treatment strategies utilized by Iowa DOT. Three are three
components to the verification study. First, we detail a single treatment strategy for a
forecast period 6-12 hours in advance of the storm onset (start of precipitation). Second,
we compare the recommended treatment and weather forecast to the actual Iowa DOT
treatment and recorded weather observations. Finally, we examine the variability of the
treatment recommendations over multiple forecast periods.
As background, there are several time series shown for each event: precipitation,
pavement temperature and treatment. The keys for each parameter are shown in Fig.
11.17 (A-C). Precipitation categories (A) are color coded for Rain (Green), Light Snow
(light blue), Moderate Snow (royal blue) and Heavy Snow (red). Road temperatures (B)
are categorized by the effective anti-icing range of salt: >35 F or warm roads (green), 14-
35 F or in-range roads (yellow) and <14 F or too cold (red). Finally, treatments (C) are
illustrated by color coding and symbols. A plow-only treatment is shown in purple, an in-
storm treatment of anti-icing chemicals is shown in green with the number inside the box
representing the recommended lbs/lane-mile to drop, pre-treatments are shown in brown
with an "L" in the box (liquid brine at 50 gal/lane-mile - 110 lbs/lane-mile dry salt
equivalent - is the expected Iowa DOT treatment), and binoculars to represent a time
period where the roads should be monitored closely for hazardous conditions (only seen
on actual treatment plots).
Fig. 11.17. Legend keys for RCTM verification variables: (A) Precipitation, (B) Road
Temperature, and (C) Treatments.
The synoptic conditions and observational data for each case study have already been
detailed in the road weather forecast system verification section (11.1). Therefore, the
data presented here are presented in a more generalized form conducive to verifying the
specific thresholds of the treatment recommendation (Rules of Practice) algorithm. All
times are in local Iowa time (Central Standard Time).
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