Maintenance & Traffic Branch
New Brunswick Department of Transportation
We are gaining increasing inventory of multi-lane divided highways carrying growing volumes of high speed traffic. Safe winter maintenance operations require special measures to clear these roads of snow and ice.
Experience has shown that many of the motor vehicle accidents that occur during multi-lane plowing operations involve vehicles passing plow trucks, then either losing control in the transition to unplowed lanes or striking the truck or plow. A common method to minimize the risk of collisions is the use of "echelon" plowing involving a team of two or more trucks plowing adjacent lanes in each direction. Trucks operating in echelon travel close together reduce the passing opportunity for following traffic. Improved safety lighting packages incorporating high intensity strobe lights and wing mount LED marking lights can help make plow trucks more visible, further discouraging passing attempts.
Even echelon plowing does not eliminate all passing attempts by following vehicles. Plow operators must leave a short gap between vehicles to maintain safe operating distances, particularly during poor driving conditions. Because the conventional right-hand wing of the lead vehicle extends into the driving lane, it is exposed to traffic taking advantage of the gap and cutting in between the plows. Again, the situation is worse during poor driving conditions when the wing may be obscured by a cloud of snow. Almost every year there are several collisions involving vehicles striking the lead vehicle wing or the dense snow cast from the plow and wing.
Echelon plowing with conventional right-hand plows and wings suffers from reduced efficiency. The following plow must pick up and throw all the snow cast by the lead vehicle. Snow densifies each time it is handled, so in addition to having to handle the snow twice, the plow must push a denser mass of snow off the traveled lanes.
Mounting a left-cast plow and wing on the lead echelon vehicle solves many of the remaining echelon plowing problems. The lead vehicle casts all the snow it collects to the median so the following vehicle only has to clear its own lanes. The left-hand wing extends over the median shoulder and not into the driving lanes. If a vehicle does attempt to pass between the plow trucks it will not encounter any equipment extending past the plow truck profile and no cast snow or windrow to cause it to lose control.
A dedicated left-hand cast plow and wing lacks flexibility as it is restricted to use only on multi-lane, wide-median highways. A better solution is the use of a reversible plow and switchable wing mounting. The plow can then be used for all multi-lane and conventional operations by swinging the plow and mounting the appropriate wing. Plows and the associated frames and rigging add weight to the front axle of the trucks. The switchable wing mounting minimizes the risk of overloading the front axle by eliminating the need to mount both left- and right-hand wings at the same time. Quick connect couplers make it possible to use a single set of valves and hydraulics for a wing mounted on either side of the truck.
Switchable wing adopted
In 1995, the New Brunswick Department of Transportation acquired two trucks with reversible plows and switchable wings for trial use on two sections of multi-lane divided highways. Design and fabrication of the wing mounts was done in-house by the NB Vehicle Management Agency. The configuration immediately proved effective and the department began specifying reversible plows and switchable wings for other extensive multi-lane divided highway routes. The 420-truck provincial plow fleet now includes 15 trucks equipped with reversible plows and switchable wings.
Several improvements have been made to the switchable wing set-up since the original pilot configurations. Many of the improvements have been direct results from suggestions from the plow truck operators. One of the first design changes was an alteration of the left-side mount to "tuck" the wing into the truck cab below the driver's window to increase driver side visibility. Next, the front slide travel was increased to improve the shelving or benching capability of the wing in the left position.
The standard NBDOT combination plow truck uses a side discharge out a chute or spinner mounted immediately behind the driver side door. This configuration enables the operator to discharge salt along the highway centerline on two-lane roads. When plowing in echelon on multi-lane roads, it has been common for the lead vehicle to plow without applying salt, depending upon the following vehicle to salt both lanes using the spinner. Modifying the spreader on the lead plow trucks to throw salt under the truck makes it possible for both vehicles in echelon to salt. This requires less spinning, reducing bounce-back and salt losses to traffic, especially important when anti-icing early in a storm.
The switchable wing mounting is not without limitations. Drivers find it somewhat disorienting when carrying the left-hand wind through town on the way to a route. They find they have to pay extra attention to prevent the wing from hanging over the centerline.
Although the wings are easily interchangeable from the left to the right side, the job takes from 15 to 30 minutes and must be done in the yard or shop. Drivers cannot switch mid-route. If the left-hand wing is mounted, it is difficult or impossible to use the wing on any two-lane or even median-barriered sections of a plow route. Two-lane sections must be done with just the plow, leaving a windrow which must be cleared with an additional pass.
Proving their worth
The switchable wings and reversible plows have proven to be valuable tools when used on wide-median, multi-lane, divided highway routes. Their use has improved plowing efficiency and significantly reduced the number of run-up collisions. Operators of the following trucks appreciate the improved visibility due to the elimination of the snow cloud generated by a right-hand wing equipped lead truck.
The flexibility of the wing mounting combined with the reversible plows means that the trucks are not committed to lead plowing or even multi-lane plowing. It is possible to convert lead trucks to cast in the opposite direction to plow on a secondary route with only a quick visit to the yard.
For more information, please contact Dave Macfarlane at (506) 453-2600 or at Dave.Macfarlane@gnb.ca.