If you've been following our US 89 updates on Facebook or YouTube you know that we have been talking a lot about geotechnical engineers lately. Today, we want to take a look at one of the tools they work with: inclinometers.

When engineers suspect a slope or embankment might be moving, they can use an inclinometer to see if their hunch is correct…

But, what’s an inclinometer?

An inclinometer is a device that measures the slope inclination (movement) at a specific location.

ADOT Geotechnical Operations Manager J. J. Liu explains that an inclinometer consists of a precision-tooled plastic casing (it looks basically like PVC pipe) that has internal grooves carved out of it.

That casing is installed into the ground through a vertically drilled hole.

Next, the casing is weakly grouted into place, allowing it to shift with the ground when (or if) it moves. A probe (not just any probe – this one measures tilt and can calculate the magnitude, direction and scope of any ground movement) is then inserted into the casing in order to measure the inclination at various points along the length of the casing.

“The inclination data is compiled and compared with a baseline reading, which we obtain right after the inclinometer is installed,” Liu says. “The difference at each elevation is the magnitude and direction of the movement at that elevation.”

We mentioned the internal grooves above and we don’t want to forget about those…

Inclinometers out in the field.

The grooves are on the inside of the casing and serve as a kind of track for the inclinometer probe (the probe has guiding wheels – did we mention that? You can see them in the photo above).

So, the wheels sit in the grooves and measurements of the inclinations at various points are taken by the unit as the probe is pulled up from the bottom of the casing.

Hopefully this is making sense, but if not, try to picture a big milkshake (it can be any flavor!).

We’ll say it’s a very thick milkshake … thick enough that you can drill a hole through the ice cream, all the way down to the bottom of your glass. Now imagine sticking a big straw down that hole that you’ve just drilled out.

The straw is kind of like the casing that we described above. If the milkshake moves or shifts a little bit, the straw is going to move along with it.

There’s no real food analogy to go with this next part, so we’ll just say that you’ll place a probe (that same sophisticated probe we described earlier – the one with the wheels that can calculate the scope and direction of any movement) down the hole of the straw…

You’ll use the probe to take periodic readings and, over a period of time, you’ll know how much your shake is shifting.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Guardrails. You see them all the time, right? But, how often do you really think about the important job they’re performing?

If your answer is, “never,” that’s perfectly fine and, quite frankly, it’s what we expected, because who sits around contemplating guardrails?

But, guardrails really do perform a vital task, which is to separate vehicles from a non-traversable slope past the edge of the roadway or any type of fixed object (think power pole or building). They’re also the topic of this blog post, so hopefully your interest in guardrails is now sufficiently piqued!

How they work

First off, there are different types of barrier out on the state’s roads, but what you see on many highways (and what we’re talking about here), is the w-beam guardrail that is secured to wooden posts (see photo above). Fun fact: It’s called a w-beam because if turned on its side, it looks like a W.

When the guardrail is hit by a vehicle, the posts move back and rotate with the force of the vehicle. The wooden posts, the w-beam, the dirt and the vehicle all absorb some of the impact, but the idea is that the w-beam will stay intact and will prevent the vehicle from traveling off the side of the road into whatever obstacle the guardrail is there to protect you from.

The energy of the impact is distributed to many of the posts, which are able to hold the w-beam against the vehicle, allowing the vehicle to come to a stop without crossing the barrier or flipping over it.

We don’t use them unless we have to

Guardrails are only used when necessary. If a road can be built to avoid the need for guardrail, that’s typically the way to go, but it’s not always possible.

We won’t get too technical, but engineers do have calculations for determining whether or not to use guardrail that take into account speed, traffic volume and the amount of clear area that there needs to be.

If it is determined that guardrail is needed, engineers also have to figure out how much is necessary. The term, “length of need” refers to the length of guardrail needed to shield the motorist from the potential hazard. Again, we’re not going to get technical here, but there’s a formula to calculate the length of need, too.

But wait, there’s more!

If a guardrail is hit, there’s some maintenance involved. According ADOT Maintenance Superintendent Craig Cornwell, his crews are out there repairing guardrail hits just about every day.

He says the w-beam railing comes in sections (from 12.5 feet to 25 feet).

“If a section is damaged, we replace that whole section,” said Cornwell, adding that the beams actually overlap and are connected to each other with eight bolts (there’s also a big bolt (about 18 inches) that connects the beam to the wooden post.

On top of repairs, Cornwell says his crews perform routine maintenance on the guardrails, which includes regular inspections.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Next time you’re traveling uphill only to get stuck behind a slow-moving vehicle or truck, you’ll appreciate the concept of a climbing lane.

A climbing lane is an “extra” lane that’s used for short distances in certain areas to improve safety, ease congestion and prevent delays. These lanes help facilitate the passing of trucks and slow moving vehicles whose speed drops because of the sustained steep grades.

A few more facts:

• A climbing lane looks the same as any other lane and is the same width.
• Climbing lanes usually are used on uphill segments of highway that have a steep grade (usually 5-6 percent grade).
• Climbing lanes typically are marked with signage advising slower traffic to keep right.

“Climbing lanes help reduce collisions and backups by providing slower moving trucks and vehicles an additional, safe lane to travel in. This reduces conflicts between slower moving trucks and passing vehicles,” said Prescott District Engineer Alvin Stump in a recent news release focused on a new ADOT project involving a climbing lane (we’ll tell you more about that tomorrow!).

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

Most drivers are probably familiar with pavement markers…

They’re the reflective objects typically placed on the road in between pavement stripes – you’ll often see them along the solid pavement lines, too, or on exit/entrance ramps. Basically, they’re used to give drivers a better guide at night.

Nothing new there, but did you know that the markers can vary depending on their location?

That’s right … if you travel up north you may notice that the pavement markers are recessed, rather than raised as they are in most other parts of the state.

Any ideas why that is?

We asked ADOT Project Supervisor Rick Schilke for an explanation and he says it has to do with snowplows.

A diagram of recessed pavement markers.

“Up here, we sink the pavement markers down for the plows, otherwise they’d just pop right off,” he said.

Makes sense to us!

Installing recessed pavement markers requires a little more work than the raised markers. Schilke says crews must grind a groove into the road that tapers down at an angle allowing for reflection. The marker is then put into place with an epoxy.

One more thing to note: In areas where snow is expected in the colder seasons, ADOT crews actually recess stripes, too. (We’re not talking about painted stripes, ADOT uses striping “tape” that’s more durable and reflective than paint.) The striping tape is recessed so that it won’t be displaced by snowplows.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

We’ve got a blog post coming up real soon that’s going to focus on Dynamic Message Signs (Don’t know what those are? Keep reading!).

That blog post isn’t ready quite yet, so in the meantime we wanted to at least get started by defining a couple of terms for you …

First up, Dynamic Message Signs: These are the large signs over/near roadways used to display messages to the public. You’ll often see travel times posted on these signs during rush hours or safety messages and other travel information.

The larger DMS have three rows of 18 characters. Each of those characters measures 18 inches tall.

Now that you know what DMS is, take a look at a Node Building. These “buildings” are about the size of a typical storage shed and are located near the roadway. There are several node buildings in the Phoenix-metro area.

Node Building

These nodes are filled with equipment capable of collecting regional information (e.g., from various controller cabinets) and sending it to the TOC. Node buildings are equipped with fault tolerant air conditioning systems to maintain moderate summer temperatures.

OK … now you’ll have to stay tuned for a more in-depth blog post on Dynamic Message Signs.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

This item probably looks pretty familiar to any of you photography buffs out there. It’s a roll of film – a really big roll of film.

In fact, if you were to unroll it, the film would measure 9.5 inches by 250 feet!

But, what does this have to do with transportation, you might ask?

Remember yesterday when we blogged about Photogrammetry? We told you that the sophisticated maps created by ADOT photogrammetrists all start off as two aerial photographs.

The pair of aerial photos (called a stereomodel) is turned into a very accurate map that’s used for a number of purposes including helping engineers design roads.

Well, this is the film required to take those initial aerial photographs.

ADOT has a very large camera that is placed in an airplane specifically to get these aerial shots. After an area is flown and the photos are captured (about six exposures per mile for design level mapping), the film is developed.

The film is archived and kept in a climate-controlled room.

Next, the very detailed photos are digitized by a powerful scanner (not your typical desktop scanner).

There’s a lot of information and detail in these photos so a large file size is required … one image equals about 267 megabytes for a black and white imagery.

From there, the digitized image is sent to the photogrammetrists so they can begin their work.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

We’ve got another definition for you, and like last time, this one is related to construction sites.

A Lost Deck is basically a temporary wood framing system that is put in place prior to the rebar and “real” bridge deck being cast. It is built and set at a certain elevation to give the concrete from the “real” deck its proper thickness.

Once the concrete from the real deck is poured, there’s no way to retrieve the lost deck, hence its name.

While the lost deck doesn’t serve much of a purpose once the concrete from the actual deck has dried and strengthened, it is engineered false work that has to be designed to meet certain specifications and carry the weight of the rebar and wet concrete.

The photo above is the lost deck inside the bridge at Waddell Road and the Loop 303.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

This blog’s “Building a Freeway” series is our attempt at explaining the many steps involved in constructing a major transportation corridor...

We’ve visited several construction sites in order to share with you this up-close look at the process, but we have to admit sometimes we’ll see some construction-related object and have absolutely no idea what it is.

It’s a good thing there are plenty of people on the site of whom we can ask: “what is that?”

We thought we’d share their answers here on the blog and we’ll get started with rebar caps.

A rebar cap is a special steel-reinforced plastic “mushroom” cap that is placed on protruding rebar at construction sites.

Rebar caps protect from injuries.

Even though it’s small, it serves an important purpose: these caps provide protection from injuries. An exposed piece of rebar can mean scratches and minor injuries … or, worse, if someone were to fall from above onto a piece of rebar that’s sticking up. Rebar caps protect from injuries.If there’s a long row of rebar, a 2x4 piece of lumber can actually be placed on top of these caps providing another layer of safety. Rebar caps protect from injuries. Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

All Arizona state highways have mileage markers.

These reference “posts” are set two feet off the right shoulder and are about one mile apart.

Mile posts can be used to tell where you are located if you are involved in a collision, have mechanical problems, or are out of gas. If you have to stop, note the route you are on and the approximate distance from a mile post.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!

When you see signs directing you to tune in to a certain radio station for construction information, do you ever wonder where the signal is coming from?

Chances are a nearby Highway Advisory Radio transceiver is helping to deliver the message.

Used to give special announcements within a short distance, HARs are often used in Arizona for rural road construction.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!