UDOT’s new Diverging Diamond Interchange is sweet when it comes to mobility and safety.

A new DDI at Bangerter Highway and State Route 201 is in operation, and drivers should notice less traffic delay right away. The intersection has safety improvements too. A DDI is more efficient and safer than a regular intersection because of fewer signal phases and conflict points.

The new intersection at Bangerter Highway and SR-201 improves mobility and safety.

When it comes to efficiency, understanding traffic signal cycles and phases within those cycles is the key. “Traffic signal timing is like a yummy apple pie – think of the entire pie as the total green time for the intersection in all directions,” says Taylor. Fewer phases within a cycle are comparable to getting a bigger piece of pie.

At a regular intersection, signals need phases to allow for left turns so “we have to divide up the pieces of the pie into 4 pieces,” explains Taylor. Those “pieces” or phases include the primary street through traffic, primary street left turns, secondary street through traffic and secondary street left turns.

On some busy city streets, no one would be able to turn left without protected left-turn phases. Adding phases, like protected left turns, makes the cycle length longer. For good traffic progression, signal operators try to make the cycle length just right – not too short, not too long. A too-short cycle can create delay when too few cars can pass through. Long cycles reduce traffic speed and can make progression sluggish.

“DDIs are more efficient because of fewer phases,” explains Taylor. Eliminating left turns mean that the green time that you would normally give to the left turn can be given to other movements.” A DDI eliminates left turns on the primary street movement, making the pie pieces bigger for the other competing movements.

Taylor adds that left turns are necessary but generally inefficient. If the capacity volume of a left turn is low compared to the through movements, any green time that can be taken from a left turn movement adds to the overall efficiency of the intersection. “Slicing the pie piece larger for the through movements is much more efficient. The left turn equivalency factor is commonly between 2 and 3, meaning that a left turner looks like 2 to 3 through passenger cars.”

DDI’s are safer because of fewer conflict points.  A conflict point occurs when two cars have the potential of being in the same place at the same time if every direction had a green light. According to Taylor, “a diamond interchange contains 30 conflict points; a Single Point Urban Interchange has 24; a DDI has only 18.  Fewer conflict points are safer.”


The I-15 CORE project team does its homework before placing concrete.

A concrete curing/tinning machine on the I-15 CORE project.

At a month past the half-way point, workers on the Utah County I-15 Corridor Expansion project have placed over 1.7 million square yards of concrete. “Since concrete pavement is smooth, requires less maintenance and resists potholes, it’s often a good choice on high-volume roads,” explains John Butterfield, UDOT Materials/Pavement Engineer for the project. But regardless of pavement type, “the main thing that drives pavement design is traffic.” I-15 CORE pavement is built for longevity and strength.

During the bidding process, UDOT asked for 30-year pavement. Provo River Constructors included a 40-year pavement design as a value-added feature in their winning proposal. The entire pavement section, bottom to top, consists of four layers: granular borrow, drainable granular borrow, asphalt base and 12 inches of Portland Cement Concrete Pavement on top. Together, the layers in the pavement achieve a structural value that is predicted from the road’s expected traffic volume.

Making sure the top layer of concrete meets final acceptance — and lasts that expected 40 years — starts with an understanding of how the specific concrete mix design will cure. For that important task, the I-15 CORE project team uses maturity meters — electronic sensors embedded in concrete and handheld readers. Using maturity meters has become standard practice in the building construction industry and is common in road construction.

Do the math

Before concrete is placed on the I-15 CORE project, “there is some homework that’s required,” says Butterfield, who explains the process. Because the compressive strength of a specific concrete mix design has a relationship to time and temperature, a maturity curve that shows that relationship can be charted. When inserted into core cylinders, maturity meters can be connected to a reader to access information on time and temperature, making the process very precise.

Data is collected by casting concrete cylinder samples and tracking the time and temperature of the concrete as it cures and gains strength. Then, the cylinders are broken at pre-set intervals to determine compressive strength, and that data is recorded and correlated to the time and temperature data.

Progressing work or allowing traffic on the pavement

Once data is collected and plotted, the “homework” maturity curve becomes an appropriate basis to measure the strength of in-place concrete. Workers assess concrete strength simply by taking a quick electronic reading in the field from data loggers embedded in the pavement. When the correct concrete strength is reached, work can progress or traffic can be allowed on the pavement.

For final acceptance, traditional cast cylinders made from the same batch as in-place concrete are still broken to measure 28 day compressive strength. However, for determining interim strength for the purpose of progressing subsequent work, maturity meters are a more efficient, precise and less expensive method than casting and breaking several additional cylinders.

“One of the greatest benefits of maturity meters is that they provide the strength of the actual ‘in-place’ concrete,” Butterfield says. “We no longer have to break cylinders, either lab-cured or field-cured, and speculate how closely they correlate with the strength of the actual structure.”


SLIDE SHOW: Concrete is monitored and tested for strength in order to progress work, allow traffic on the pavement or to determine final acceptance.

The compressive strength of concrete has a relationship to time and temperature specific to the mix design. As concrete hydrates, it cures and gains strength. Hydration occurs as the cement becomes fully saturated by the water in the concrete. The hydration process produces heat. Taking time and temperature readings of the concrete as it cures and gains strength allows workers to track the curing process.

(Click on the large images to see captions. Choose images by placing cursor in the black area below.)

Created with Admarket’s flickrSLiDR.


The Manual for Assessing Safety Hardware updates the size of test vehicles to more closely match what’s on the road today.

All permanently installed and temporary roadside hardware – including sign bases, crash cushions, traffic control devices, and various kinds of barriers, is crash tested according to standards established by the National Cooperative Highway Research Program. New standards for crash testing have recently gone into effect, and are detailed in AASHTO’s Manual for Assessing Safety Hardware. The new manual replaces NCHRP Report 350.

This video shows crash testing using MASH standards.

The MASH updates protocol for vehicles that are used in crash tests to more closely match what’s on the road today. The new crash test criterion is being used on all roadway hardware being produced since January 2011. NCHRP Report 350-tested hardware is appropriate when replacement is necessary, and re-testing is not required. UDOT will update roadway hardware with MASH tested products as necessary – the old hardware in place now is safe.

Although crash testing took place as early as the 1930’s, standards that establish criteria for tests have been in effect since 1962 with sedans specified as a test vehicle. As crash testing has continued through the years, understanding about the practice has improved and updates that add more criteria and different procedures have been added. For example, a 1974 NCHRP update added a small car and also added tests for transitions, terminals, crash cushions and breakaway supports. A 1980 update added evaluation criteria and modernized procedures to conform to available technology and practices. In 1993, a pickup was added as a test vehicle to represent small trucks and minivans in use.

The Texas Transportation Institute is one of the first organizations to crash test hardware, including sign bases and crash cushions. The TTI facility, a decommissioned military air base, has long concrete runways that make a good setting for the tests. The modern TTI crash test video below shows a crash test of a concrete barrier on a mechanically stabilized earth wall using the larger truck specified by the new MASH standards for vehicles.

For more:

Download the MASH.

Read a recent post about tests on MSE walls.

See an interactive timeline about crash testing at TTI.

Watch a presentation about how crash test standards have changed.



UDOT’s use of an innovative traffic control system has earned national recognition for improving safety in an urban construction zone.

Using moveable barrier helped UDOT balance the needs of road users and workers by keeping traffic flowing and providing a large, safe work zone. Here, moveable barrier being adjusted to give west-bound evening commuters an additional travel lane.

The Federal Highway Administration and the Roadway Safety Foundation will recognize UDOT as a winner of the 2011 National Roadway Safety Award for using moveable barrier on the 3500 South reconstruction project. The annual award program honors “high achievers in the field of roadway safety” for using and documenting safety best-practices. The award will be presented on Tuesday, November 15 in Washington D.C.

While common on interstate highways across the nation, urban use of moveable barrier is less common. The flexible lane use system can be adjusted frequently to accommodate traffic flown by providing more lanes in the peak travel direction.  UDOT’s pioneering use of the innovative technology on an urban travel corridor will help other departments of transportation employ the effective safety strategy on projects with similar characteristics.

Moveable barrier helped improve safety, accommodate commute traffic, and shorten the duration of the project. The barrier improved safety by eliminating left turns, except at major intersections. Twenty to 25 fewer crashes occurred during the project, resulting in a safer roadway, less expense to road users and less delay due to crashes.

Traffic delay, which causes inconvenience, also has an associated user cost. Because morning and evening traffic flow was not severely mired, road users saved time and money. A conservative estimate shows that using the moveable barrier saved road users between $1.7 to 2.4 million by reducing travel delay and crashes during construction.

Reducing  the duration of projects is one of the most important ways UDOT limits the inconvenience of construction on road users. Using the moveable barrier provided a large, safe work area where construction could progress more efficiently. Partly as a result of the barrier, the project was completed 7 months ahead of schedule, leaving road users and businesses with a wider, high functioning roadway free of excessive delay.


A new blog uses many voices to tell Utah road users how to stay safe.

For some serious fun, take a motorcycle safety class. Rachel Leiker did so and wrote about her experience for the Highway Safety Office Blog.

The Utah Department of Public Safety, Highway Safety Office has a new blog that uses a variety of authors to promote safety. Experts when it comes to safety on the road, blog authors are personally involved in a number of important efforts. “Our office’s program managers are passionate about their programs and it shows in their writing,” says Derek Miller, Highway Safety Program Specialist and one of the authors.

The Office of Highway Safety has 13 programs aimed at all types of road users – cyclists, motorists and passengers. The programs emphasize knowing the rules of the road and making the best choices, like wearing approved protective gear when riding a motorcycle.

Many posts are also backed up by studies or statistics with punch. A Click It or Ticket post by Kristy Kay cites how high visibility enforcement of safety belt laws helps save lives: “…the Click It or Ticket mobilization is credited with helping to increase the state’s belt usage rate from 67.4 percent in 2000 to an observed rate of 89.0 percent in 2010. Belt use saves thousands of lives each year across America and seatbelts have saved an estimated 1,355 lives in Utah since 2000.” That direct message is a great example why everyone needs to buckle up!

Even though the topics are serious, authors convey messages in an entertaining way. Author Helen Knipe’s post  explains how being a cyclist helps her drive with respect, and observe the rules of the road: “When I see cyclists in the road, I see myself  (except they’re usually riding faster than I do…) I have no problem waiting to pass a cyclist, giving cyclists extra room, exercising greater caution whenever they’re around – because that’s exactly what I would want drivers to do around me when I’m on my bike.”

Many of the posts have great images and videos that speak volumes. High school student Jake Barube won an iPod touch for his visually appealing motorcycle safety video using stop motion animation.

Jake’s on-camera narrative also uses humor. He urges motorcycle riders to wear approved protective gear “unless you enjoy the taste of asphalt.” His parting sentiment, “The safer you are the more fun you’ll have” are words any parent would want their teen to understand.

Guest posts give some good safety narratives too. Rachel Leiker attended a motorcycle safety training class. In her post she says, “This is seriously one of the most fun ways to spend a weekend, and the skills you learn don’t hurt either.”

Bookmark the site and check back often!


How UDOT Uses Social Media, a guest post by Andrew Johnson, former UDOT employee.

Chances are you’ve been caught in a traffic jam, wishing you knew about it ahead of time. The Utah Department of Transportation is consistently making strides to keep Utah drivers informed before they get behind the wheel, and a large part of UDOT’s efforts is through the use of social media. (NEVER Tweet and drive!)

UDOT’s innovative approach to keeping commuters up to speed includes regular updates through their Twitter feed. This gives drivers access to real-time information about road closures, accidents, construction projects and abnormal delays, and also provides the public with direct access to UDOT employees.

Here’s an example of a recent conversation on Twitter:

Tweets keep motorists informed — CLICK TO ENLARGE.

In this example, someone Tweeted UDOT with information about a possible malfunctioning traffic signal. UDOT responded to the Tweet, and included the signal technicians at the Traffic Operations Center to relay that information. At that point, the technicians dialed into the signal, and were able to diagnose a potential problem. Since Twitter is a public forum, and anyone who is following @UtahDOT can see the conversation, other people may join the dialog and contribute information. I noticed the Tweets, and was able to contribute my two cents.

UDOT Traffic is another fantastic resource available with the click of a mouse or the swipe of your smart phone. UDOT Traffic includes a network of closed-circuit television cameras, electronic variable message signs, coordinated traffic signals, traffic sensors, ramp meters and weather stations. Together, this network delivers real-time information directly to employees at the Traffic Operations Center and to the UDOT Traffic website. Employees can take the information received at the TOC, relay that information on Twitter and Facebook, and thousands of people instantly receive that information and can plan their routes accordingly.

Travel times help road users to decide to continue as planned or to take an alternate route.

As you travel along Utah’s freeways, you may notice large black signs spanning across the lanes overhead. These are called Variable Message Signs, or VMS, and are extremely effective in communicating important information to public. Located at key points across the state, these signs are controlled by operators at the UDOT Traffic Operations Center, and can be activated with custom messages as needed. The messages on these signs are governed by UDOT policies, and format, length and wording is dictated by the Manual on Uniform Traffic Control Devices (MUTCD) by the Federal Highway Administration.

These signs provide drivers with clear, concise messages about freeway conditions, and drivers can then decide if they want to continue on the same route or choose an alternate route. VMS boards can also be coordinated with other State agencies like the Department of Public Safety to run messages about safety belt laws, and other public safety campaigns. You may also see messages about air quality alerts through the Utah Department of Environmental Quality.

Despite the integration of social media into their arsenal, not all of UDOT’s efforts into reducing delays for drivers are strictly reactionary. In fact, a large number of construction projects around the State are a response to future demands, and UDOT wants to make sure Utah’s transportation network is efficient for years to come.

Information and pictures provided by 24saltlake.com.


UDOT and state agencies across the U.S. are using Social Media in innovative ways.

With the rise in use of social media, it makes sense that government agencies are taking advantage of relatively new online communication tools like Facebook and Twitter. A recent post on this blog describes how UDOT uses social media, and the agency is not alone among transportation organizations across the nation. State government social media users are finding a variety of ways to use Social Media and free online and smart phone apps to provide quick, effective ways to communicate with citizens.

Advantages to government agencies abound when it comes to Social Media use. The primary advantage is that Social Media lets transportation agencies hear the concerns of citizens and engage in a real time two-way conversation.  Applications like Facebook and Twitter let real two-way communication with people in the places where people are already congregating and sharing ideas.

Social media can also help DOTs:

  • Expand communication reach more people and other audiences.
  • Address misconceptions
  • Be cost effective with communication efforts
  • Increase the speed of public input
  • Target specific audiences or neighborhoods about a project or issue

Here are some innovative ways UDOT and agencies from other states are using social media to interact with the public:

While the in-person meeting was taking place, project representatives answered questions posed by online attendees via laptop.

UDOT used a free online application to hold an online public meeting simultaneously with an in-person meeting. The application has a chat feature and also integrates easily with cameras and microphones. Meeting organizers invited attendees to sign up for the online meeting ahead of time. While the in-person meeting was taking place, project representatives answered questions posed by online attendees via laptop. Periodically, representatives gave an overview of the purpose of the meeting and urged public feedback. Using the online application helped organizers to expand the reach of the public meeting to citizens who could not attend in person.

Washington State Department of Transportation has had good success using Twitter and blog posts together during weather emergencies. Twitter is a good tool to report and answer questions about closed roads or the status of storms or other weather events. Tweets can direct users to the WSDOT Blog for more information.

The California DMV used Social Media to optimize customer service communication channels.  The agency has grown its online presence by posting useful information, such as how to choose a good car seat, on Facebook. Twitter has been helpful for answering questions from citizens. The California DMV even launched a smart phone app earlier this year to reduce the frustration people experience while waiting in line. The free app shows DMV locations and wait-times. Other features of the app let users schedule a time to take a written test, and even see the testing material and take a practice test.




A Diverging Diamond Interchange and Auxiliary Lane project will improve mobility and safety at the Bangerter Highway, SR-201 intersection.

The DDI intersection made its Utah debut in American Fork with the  Pioneer Crossing project. Now, UDOT is using the innovative design to improve traffic flow at Bangerter Highway and SR-201.

In addition to the DDI, the project will also add a traffic lane between Bangerter Highway and I-215, dual right-turn lanes onto the SR-201 eastbound on-ramp, dual northbound left-turn lanes on Bangerter highway at 1820 South and dual eastbound left-turn lanes at 2100 South Frontage Road to northbound Bangerter Highway. Together, the new intersection and lanes will reduce delay through the intersection and along the intersecting corridors in the area.

Reducing delay

DDIs reduce delay by eliminating left turn signal phases. In typical diamond intersections, through-traffic waits for left turning traffic accessing on and off-ramps. Without a left-turn phase, through traffic can proceed without waiting for left turning vehicles.

A DDI also eliminates the need for signals at the on and off-ramps. Vehicles using the ramps have free right and left turns and simply wait for a gap in traffic.

Since traffic patterns vary depending on location, traffic analysis must always be done to make sure a DDI is the best choice.  Studies show that the DDI is a good fit for this location.

A cost effective choice

In addition to supporting better mobility and safety, the DDI is also a good cost saving project at this location. Because the existing bridge has adequate space, UDOT is rehabilitating the bridge deck and adding striping and signals for the conversion.

The DDI project is part of UDOT’s Bangerter Highway 2.0 , an expansive upgrade that includes improvements from the Salt Lake City Airport to 13400 South. The effort will reduce travel delay on Bangerter Highway by incorporating the latest innovations in transportation mobility.

Ultimately, the project will achieve all four of UDOT’s  strategic goals known as the “Final Four”: Take Care of What We Have, Make the System Work Better, Improve Safety and Increase Capacity.



Salt Lake City recently participated in a national effort to document the use of bicycle facilities on city streets.

"From the most casual recreational rider to the daily commuter there is a large population that rides," says Andrew Coffey, who coordinated a volunteer effort to count cyclists in Salt Lake City.

Salt Lake City has collected some data that will be available for engineers planning improvements to city streets and intersections. The Institute of Transportation Engineers  Pedestrian and Bicycle Council and Alta Planning co-sponsor the yearly  National Bike/Ped Documentation Project to provide local and national data showing how transportation facilities are used by cyclists.

According to the project website, “without accurate and consistent demand and usage figures, it is difficult to measure the positive benefits of investments in these modes…This nationwide effort provides consistent model of data collection and ongoing data for use by planners, governments, and bicycle and pedestrian professionals.”

Evelyn Tuddenham, UDOT’s Bicycle/Pedestrian coordinator says UDOT will conduct similar counts in the future. “Until you do the research, you really don’t know” if, when or how facilities are being used.

Andrew Coffey, Political Science Major at the University of Utah, coordinated the effort for Salt Lake City. He usually spends time studying international conflict and domestic politics. His internship with the Hinckley Institute of Politics offered something completely different – a chance to count cyclists.

Andrew Coffey U of U intern, counting cyclists on North Temple.

Coffey coordinated a bike count, modeled after accepted ITE methods for documenting vehicle usage, starting on August 23. “I was immediately handed the bicycle count project that day,” says Coffey. Coffey worked with Becka Roolf, Bicycle and Pedestrian Coordinator for the Salt Lake City Transportation Division.

The all volunteer effort took place during four days in August on selected intersections. Coffey solicited from and got great support from the cycling community. Results of the count will be released soon at an event held to thank volunteers for helping.

Coffey enjoyed his project. “Cycling can truly be an alternative method of commuting within the Salt Lake Valley, he says. “Even if you don’t ride your bike as your primary method of transportation, it is good to see that Salt Lake City strives to provide great facilities for bicycle riding.”

As he watched traffic and cyclists, he was troubled by the lack of helmet use among cyclists. He also noticed that like motorists, cyclists don’t always know the rules of the road. One thing that surprised him – there are a lot of, and many kinds of cyclists. “From the most casual recreational rider to the daily commuter there is a large population that rides.”