Simulations show ways to boost plow
productivity up to 90%
off-the-shelf software help develop a more cost-effective roadway snow plowing route? In
simulations in Ottawa, operators plowed software-optimized routes from 60 to 90 % faster.
W. Maxwell Miner, P.Eng., is a
project engineer with the City of Ottawa (Canada) Department of Engineering and Works.
This article first appeared in
the April 1997 edition of BETTER ROADS magazine
During the winter months, the City of Ottawa's Operation
Branch employs 220 wage field staff, 30 to 50 staff from a casual employment pool, and
operates and supervises over 300 pieces of equipment. During typical storm clean-up
operations, the branch hires up to an additional 75 hired graders over and above the
current 10 city-leased graders, 120 snow haulage trucks, and 10 to 15 sidewalk plows in
addition to the current city-owned/leased 40 sidewalk plows. All this labour and
equipment clears snow from 456 mi. of city streets, 136 mi. of regional roads, 25 mi. of
NCC streets, and 600 mi. of sidewalks and pathways.
The city receives, on average, 86.5 in. of snow per year.
The city performs an average of 10 full roadway plowing events on more than 60
predefined roadway plowing beats, 100 full salting events over 22 predefined salting beats
city-wide, 40 sidewalk plowing events on more than 70 predefined sidewalk plow beats, and
four to eight full snow removal operations on over 340 mi. of streets.
The winter maintenance budget for the corporation is
approximately $10 million. The corporation is also responsible for the winter
maintenance of the regional road network inside the city limits, on which an additional $6
million is allocated. If a small percentage reduction in mileage could be
accomplished, or if operation efficiencies could be introduced, immediate savings could be
realized when applied to the hired equipment fleet (that is, equipment hired by the hour).
The current roadway plowing route, or beat system, consists
of streets geographically sectioned off within the city. For example, a beat could
be all residential streets between Woodroffe, Maitland, Carling, and the Queensway.
The streets within a plow beat are listed roughly in order or priority, as well as in
order in which an inexperienced or unfamiliar operator could plow them. As an
operator becomes more familiar with a beat, he or she will modify the plowing sequence to
maximize right-hand turns and minimize left-hand turns. Sidewalk plowing beats have
been developed over time in a similar manner.
Salt beats fall victim to different operating parameters
(that is, salt application with the underbody in the upward position, salt application
with the underbody in the downward position, hopper capacity, salt dome location, and so
In response to information on arc-routing software (as
opposed to point-to-point routing) collected through a number of sources, our staff
initiated a search into the various off-the-shelf software products that could perform
this type of routing for winter maintenance activities.
After identifying five different vendors that claimed to
provide arc-routing optimization, and after measuring the functionality of each software
package against a set of predetermined requirements laid out by operational staff, the
GeoRoute software package emerged as the only package capable of performing route
optimization for winter maintenance activities with a minimum of custom modification to
the software or to the graphical map data currently available.
The purchase price for the software and the graphical map
is approximately $60,000. Also, before analyzing and implementing optimized beats,
in-house staff would be required to populate the GeoRoute database and be trained to
operate GeoRoute software.
At this point in its evolution, this approach
to route optimization was deemed to be too expensive an undertaking for an as yet unproven
savings, especially with the expense coming from operational accounts.
As a result, a local consulting firm, the PSR Group,
experienced in the application of GeoRoute for winter maintenance activities and licensed
with GeoRoute software, was contracted to conduct a pilot project.
The study's objective was to investigate the costs of
designing computer-optimized roadway plow beats. An associated field trial was
included to verify any operational savings or identify any operational concerns which the
implementation of optimized beats might introduce.
The winter maintenance activity chosen as an area for
potential savings and operational improvements was roadway plowing. The rationale
behind selecting this winter maintenance activity was based upon the fact that a
significant portion of the costs are incurred by hired equipment and not by full-time city
staff. For each roadway plow run, the city hires 75 graders and their associated
operators by the hour to complement the 10 leased graders operated by city staff. On
average, a typical plow run takes approximately 12 to 18 hrs., and there are, on average,
10 plow storms per winter season. Using these figures, the hired grader costs per
winter would be $675,000 to $1,000,000. A 10% reduction in the time it takes to plow
a beat could represent $100,000 in current year savings.
The GeoRoute software requires three types of data:
graphical street network data, attribute data for each street section, and vehicle
The graphical street network data used for the project was
the computerized network available through StatsCanada. Included with this data set
was street address ranges by side of the street by block, as well as street name, from
street, and to street; all indexed by a unique section number.
The attribute data was supplied by the city. It
included street width, street length (although, the network editor can also calculate the
object length of each street segment), number of lanes, whether the street is one-way or
two-way, and so on.
The vehicle data was supplied by the city, and detailed the
performance capabilities of the roadway plowing fleet, which, in this case, were all
graders. Although the city does not have different vehicle types performing the same
winter maintenance activity, the software can accommodate different vehicle types, vehicle
speeds, and so on. Typical data required by the software would include travelling
speed (while plowing), deadhead speed (blade up), as well as some operational assumptions,
such as U-turn duration (that is, extra time included to tuck snow into snow banks around
a corner), and duration to cross a street.
The consultants were asked to simulate three separate
1. Simulate the current roadway plow beat in Woodward, and
maintain the plowing sequence documented on the beat sheets.
2. Simulate Woodward's current roadway plow beats such that
the physical streets remain the same for any particular beat; however, only re-sequence
the order in which an operator would drive the beat.
3. Simulate the beats as the GeoRoute software would
re-sequence and optimize the beats.
In a city routes re-sequenced scenario, GeoRoute
illustrated that productivity gain can be achieved by simply re-sequencing the streets in
an existing plow beat. Although 18 graders are still required to plow the
re-sequenced tandem beats, based on the GeoRoute software, the longest plow beat now takes
only 5.5 hrs. (versus 6.5 hrs.) to complete, and the shortest takes 2.0 hrs. (versus 2.1
hrs.) to complete, with the average duration of all 9 beats being 3.5 hrs. (versus 4.2
hrs.). This approach would provide a more consistent level of service to the city's
arterial and collector streets.
Similarly, although 24 graders are still required to plow
the re-sequenced single beats, based on the GeoRoute software, the longest plow beat now
only takes 8.0 hrs. (versus 11.9 hrs.) to complete, and the shortest takes 2.5 hrs.
(versus 3.7 hrs.) to complete, with the average duration of all 24 beats being 5.0 hrs.
(versus 6.9 hrs.). Again, it appears that re-sequencing the order in which an
operator should drive a beat would provide a more consistent service to the residential
When routes were optimized, plowing time was cut even
more. A first attempt at optimization fixed the time for completion of arterials at
3 hrs. and collectors at 4 hrs., as per the quality standards. This iteration did
reduce the time required to plow the beats, but it did not reduce the number of beats
required. When the duration to plow all arterials and collectors was set at 4 hrs.,
a reduction in the number of actual beats was experienced. Therefore, as the
difference between 3 and 4 hrs. was an improvement, relative to the variation in service
that some of the streets were already experiencing, it was decided to fix the time
required for completion of both the arterials and collectors at 4 hrs.
Once this adjustment was made, optimization reduced the
number of tandem beats from nine to eight. Based on the GeoRoute software, the
longest tandem plow beat now only takes 4.5 hrs. (versus 6.5 or 5.5 hrs.) to complete, and
the shortest takes 3.0 hrs. (versus 2.1 or 2.0 hrs.) to complete, with the average
duration of all 9 beats being 4.1 hrs. (versus 4.2 or 3.5 hrs.). This approach
provides a more consistent service to arterial and collector streets than re-sequencing
the existing beats.
Similarly, optimization reduced the number of single
residential Class III beats from 24 to 19, and also reduced the hours to complete.
When translating the number of single and tandem plow beats
and their respective expected duration's into total grader hours per storm event, the
optimized beats require 261 grader hrs., while the original beat system required 316
grader hrs. The savings on hired graders per plow storm is estimated at $4,125 for
the Woodward Maintenance District only. The estimated savings per plow storm
city-wide is calculated to be approximately $15,000, or $150,000 per year for 10 plow
Optimizing residential roadway plow beats improved
productivity in terms of miles-plowed-per-hour by 60% to 90%. Nevertheless, extra
pre-season effort must be made to inform operators (city staff and hired operators, alike)
and familiarize them with the routes or beats for which they will hopefully be responsible
throughout the winter.
Based on the trend towards increasing the use of an on-off
hired equipment fleet for winter maintenance activities, in lieu of replacing retiring
year-round, full-time staff and carrying city owned/leased equipment, route optimization
is recommended as a consistent, defensible method for preparing efficient roadway plow
In fact, due to erosion in the number of field staff
available to supervise this hired equipment (the hired equipment fleet does not come
equipped with two-way radios), route optimization is recommended as a basis for ensuring
that winter maintenance work to be tendered out to the private industry will result in a
consistent delivery of services. It is recommended that, in tendering this type of
work, consideration be given to tendering it by the metre or mile, as even the efficient
routes will take hired equipment longer to finish than needed, if they are unsupervised.