When Denver gets clobbered by a major snowstorm, as happened March 13 with the much-ballyhooed bomb cyclone event, residents have plenty of questions about the city's policies on street plowing, often voiced through gritted teeth while they're stuck in a wintry wonderland of gridlock.

Well, we've got answers. And we're passing them along to you.

We asked Nancy Kuhn, public-information director for the Denver Department of Public Works, the agency in charge of the plows, anything and everything we could think of related to clearing Mile High City roadways after a significant dumping. And Kuhn came up with extra topics, too. Her responses take much of the mystery out of this enormous task, and with luck, they'll help you process the inevitable frustration that comes with having to double (or triple) (or quadruple) the time it will take for you to get from point A to point B.

Prepare to get your Denver snow-plowing Ph.D.

Westword: How many plows does Denver have?

Nancy Kuhn: We have seventy big plows, which cover the main streets, and we have 36 residential plows — four-by-four pickups with plows that we deploy when we do the residential program. The seventy plows run regularly on the main streets in the larger snow event. We have enough drivers to put out all seventy of them.

What qualifies as a main street?



We like to describe the main streets as most streets with stripes. If you see a street with a stripe down the center, that's what we consider a main street. It's usually a mix of arterial roadways — those larger roads, like Broadway, Lincoln, Alameda — and what we call collector streets, which connect to the arterials. And residential streets are streets without stripes. If you're driving down a street and there's no stripe, that's considered a residential street in our program.

Who drives the plows?



Currently, our large plows are operated by our street maintenance staff and our wastewater operations staff. When they're not plowing, they're doing things like street sweeping, paving, pothole repair. Residential plows are operated by our Public Works and Parks and Recreation staff.

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How do you plan for snowplow use in advance of a storm?



We'll have a snow meeting when we know snow is coming to figure out when we will bring in the crews and how many. We'll look at multiple forecasts — not just the TV stations, but also contracted weather forecasters. We'll look at six to eight different forecasts and then make an educated decision about when they'll come in — what time of day and conditions. Typically, drivers work on twelve-hour shifts when we know there will be a big snow event: noon to midnight and midnight to noon. That way, we cover all 24 hours. But we can adjust those times here and there. If we know a storm is going to start at 2 a.m., we'll bring them in and start to deploy them.

When do you start plowing?



The plows typically go out when snow starts to accumulate on the city's main streets. There might be a situation where we decide to drop de-icer on the bridges and overpasses when we get some precipitation but snow isn't accumulating yet — where it's snowing but the streets are just wet and it's likely to freeze overnight. If it's a big snow event, though, we bring in all the drivers and start our twelve-hour shifts.

What kind of de-icer do you use?



We use a couple of products. One is a solid de-icer called Ice Slicer. It's a product mined out of Utah that's mostly chloride and some minerals. That product helps provide some traction on the roads. It accelerates melting when the temperatures go up and the sun comes out and helps break up snow on the streets. But downtown, we use a liquid de-icer to cut down on our use of solid matter. It reduces particulate matter that we put in the air. We use that instead of dry material for air-quality standards.

When are residential plows deployed?



We make that call based on our snow meeting. We look at how much snow is forecast and ask if the residential plows will make a difference in clearing a path to the main street. Sometimes if we don't get a lot of snow, we're basically packing down that snow and possibly making it even more slick on the roads. We call that the Zamboni effect. We don't want to run residential plows if we might make things more slick than if there was a layer of snow that might provide more traction. The residential plows work from 3 a.m. to 3 p.m. And we have room to be flexible. There was a storm in February where we thought we were only going to get a couple of inches and it started looking more like six to eight. So we asked the residential plow drivers to come in and hit those residential streets.

Is plowing handled the same way on residential streets as on main roads?



With the residential plows, we do things a little differently. We take one pass down the center of the side streets, so they're doing less of that continued pushing and pushing and widening out, and we try to shave off the top two inches of snowpack to prevent deep ice rutting. We started the program after we had a big snow season in 2006 and 2007. We had twelve or more inches of snow on residential streets and it was turning icy. We had big ruts, and that created a situation where people couldn't get to the main streets because their residential street was unpassable. So we started doing it the way we're doing it now, so folks can get to the main streets and get on their way.

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Is there a threshold you have to pass before you'll plow residential streets?



We used to only deploy the residential plows when twelve inches of snow had fallen or was forecast. But in recent years, we got enough additional staff to put the plows out more often — not just in the biggest emergency situation, but on more of a regular basis as need be. When we needed to plow the residential streets, we used to have to round up volunteers all over the city. But now we have a dedicated staff; we added a paving crew that can help on the residential plows. Typically, though, we don't plow the residential streets unless there are four to six inches. Otherwise, there wouldn't be much benefit.

Does the city sometimes try to hold off on full deployment of plows on some storms to save money?



I don't believe that's a real thing, based on having been a part of this program for many years. We've got a group of folks who have decades of experience looking at these forecasts and making good calls and deployment decisions. And we have a pretty regular, fairly steady amount of money we expect to spend on snow removal each year — about $5 million. So we're prepared for a typical snow season. Now, back in 2006 and 2007, we had multiple blizzards back to back. I think at that point they may have gone for a supplemental budget. But in a regular season, we're able to cover our snow costs. It's rare that we have to get more money for snow. But our top priorities are safety and keeping people moving. That's our primary driver.

How many snowstorms are there in an average season?



We typically get 20 to 22 snow events each year.

Do you sometimes wait to send plows out if a storm hits during heavy driving periods?



No, but when a storm hits during morning rush or afternoon rush, you've got to remember that our plows are in traffic as well. The main effect is that the routes aren't going to be completed as quickly, because we're slowing down for traffic, and it takes a little longer to go through rush hour. But we still go out.

How close do plow blades get to the street?



They float an inch or so above the street surface. One of the main reasons is so we don't catch, say, a manhole cover that could damage the vehicle. But the blades flex. They have a hard rubber/ceramic bottom, so if they're contacting an obstacle, they can provide a kind of squeegee effect.

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Do you ever plow alleys?



We do not go through alleys as part of our program. One reason for that is because there's no room to put the snow. On the street, we have the blade angled to move it to the side. You usually can't do that in an alley.

Which streets do you plow first?



The main streets are the priority, as they carry most of the city's vehicle traffic. The goal is to clear the main streets to get people where they need to go. So if we get several inches during a short period or rush hour, we may focus on the arterials and then head into the neighborhoods to work on the collector streets. And we also prioritize plowing around schools to provide safe zones for children.

Do you routinely plow some areas more than once?



That's exactly right. Our program is built so that each plow can get through its route at least once and, in the right conditions, twice in a twelve-hour shift. If a storm comes in overnight and there aren't a lot of cars on the road, or maybe the snow has stopped, the drivers are going to make a lot of progress. And we keep running those twelve-hour shifts until conditions are looking pretty good and the streets are beginning to dry out. We keep clearing and dropping de-icer as needed.

Do you plow bike lanes?



We do. For our protected bike lanes, we have new equipment that has a plow and a brush that can kind of brush off protected bike lanes. It's a neat addition to our fleet, and we hit the bike lanes as often as we do the streets — one or two times per shift. We have a lot of folks who bike year-round these days, so we want to provide them with a way to get around. They're expecting to have the bike lanes clear, expecting to ride their bikes in all conditions. But for on-the-street bike lanes, it might take us a couple of passes to get them cleared. In that case, we recommend people ride in a shared-lane situation with vehicles. I think people are used to doing that.

Can people get information about plowing online?



They can. We have a website with information about the city's snow-response program. And we also recently launched a plow tracker. In a full deployment event, we turn on our plow tracker, so you can see where they are. When both fleets are out, it's a pretty cool visual.