If you need more information about ADOT's GIS Analytics, please visit:
/planning/transportation-analysis/gis-analysis

The saying, “a photo speaks 1,000 words” holds true when it comes to data.

Because, for most people (we’re not talking about the engineers who are out there reading this!) it’s hard to pull real meaning from just a long list of numbers.

But, when you feed those numbers and information into map (it’s sort of like a photo, right?), you start to find relationships between the data.

At least, that’s the super-simplified idea behind Geographic Information Systems, a.k.a. GIS, which ADOT uses to plan, analyze, model and manage information.

ADOT’s GIS Section Manager James Meyer explains GIS as being similar to a database, but because it has a spatial element – meaning you can plot several layers worth of data onto a map – GIS is very valuable in reaching conclusions and making decisions.

For instance, ADOT could plot traffic count data onto a map along with another layer that gives pavement condition scores. From there, it would be easy to “see” where and how traffic affects the road conditions, leading to planning and funding choices.

Some of the ways ADOT utilizes GIS …

ADOT’s GIS section updates, verifies and maintains the Arizona Transportation Information System (ATIS), which is the basis for all GIS work at ADOT.

It contains a linear referencing system that can take all of ADOT’s route and milepost data and display it on a map. Meyer calls ATIS the backbone of roadway inventory data that gives a common point of reference allowing you to tie all data to a common factor – the road’s centerline.

The Highway Performance Monitoring System (HPMS) is another way ADOT uses GIS.

HPMS is a report submitted annually to the Federal Highway Administration. It contains data on every single road in the state. Some of this data includes traffic counts, ownership, surface type, etc. HPMS is used as a planning tool by FHWA and as an aid for determining the amount of federal funds that will be distributed to each state.

ADOT’s GIS section employees also provide mapping support to all of ADOT. The maps they produce go into studies, presentations and “what-if” scenarios for pre-construction that can show planners where the future roads will be and what they’ll be next to.

You’d be amazed by how much there is to learn just by counting cars (yes, cars…not cards!)…

Traffic counts are exactly what the name implies – physical counts of the traffic on a particular road – and ADOT takes them at approximately 1,400 locations around Arizona.

These counts not only tell ADOT how many cars are traveling on the state’s transportation system, but the sophisticated equipment used also determines vehicle speed, weight and classification.

The result is a continual stream of numbers … lots and lots of numbers!

Numbers that ADOT traffic engineers use to make better, informed choices.

Think about it … it would be nearly impossible to design an effective freeway if you don’t know how many people are going to be driving on it. And, you can’t design a safe road if you don’t know the expected load the pavement’s going to have to handle day in and day out.

“This drives decisions,” said ADOT’s Assistant Director of Roadway Inventory Pradeep Tiwari. “It is a critical prerequisite to decision-making.”

Short-term stations typically generate about 48 hours of data.

In addition to aiding transportation planning and design, traffic counts are required of each state by the Federal Highway Administration and help determine the apportionment of federal highway and planning funds. They’re also a necessary factor in determining air quality measurements.

There’s an interest in these numbers outside of government, too. Developers, businesses, property owners, academia and even cell phone companies rely on this information to help make a number of decisions.

In other words, knowing as much as we can about how our roads are being used is pretty important …

“It’s like taking our pulse rate,” ADOT Planner Mark Catchpole says of traffic counts. “Without taking our pulse, we don’t know whether we’re well or sick.”

Collecting the data

ADOT collects traffic count data at approximately 1,400 locations throughout the state’s 6,700-mile highway system.

Of those 1,400 locations, 175 are a continuous traffic counting station, which means they’re receiving and sending data 24 hours a day, seven days a week, 365 days a year. The remaining locations take short-term traffic counts (generally 48 hours worth of data).

Pneumatic road tubes are used at
some locations

To get an accurate account of the traffic volume in all areas of the system, the information gained through continuous counts is compiled with the short-term figures to determine annual daily averages. This also helps ADOT factor in and make adjustments for seasonal traffic variations to get the best, most accurate idea possible of what’s happening out on the roads.

Traffic counters

Chances are you probably won’t even realize you’re being counted.

The 175 continuous traffic counting stations utilize magnetic induction loops (sensors) that are embedded in the roadway. Those sensors relay information to a nearby station (they look like traffic signal cabinets mounted on poles and powered by a solar cell). The information is interpreted by software and can be read off-site by ADOT employees.

Embedded loops are used to gather data.

The short-term stations work in a similar way. Some have the embedded loops, while other spots utilize pneumatic road tubes to serve the same function as the loops.

The short-term stations are less visible – crews must either place a battery-operated traffic counter machine in a roadside pull box that is connected to the loop sensors or chain it to a signpost if connected to a road tube.

Reporting the data

All of this data is available to the public online. For more information on traffic counts, visit the ADOT Data and Analysis webpage.