Located in Western Oklahoma, approximately 50 miles from the border with Texas is Elk City, Oklahoma. The city, which is off of the famous Route 66, has a population of approximately 11,500. While the historic route no longer exists in its original form, there is still significant traffic in this part of Western Oklahoma. When the Oklahoma Department of Transportation (ODOT) designed a project for the area, it was a unique solution that befits the traffic that utilize the roads.Today, Interstate 40 and State Highway 6 go through Elk City. In 2015, the existing twin bridges on SH 6 over I-40 were deemed structurally deficient. As ODOT began considering the project to replace the bridges, they also took into mind the on-ramps that were experiencing delays and backups.

Ultimately, ODOT decided to create a Diverging Diamond Interchange (DDI). While there are over 100 DDI’s in the United States, the Elk City DDI will be the first in Oklahoma – although others are currently in the pre-construction phase. The innovative design offers a proven solution for improving traffic flow and safety at an interchange.

Recent surveys show that 10,000 vehicles travel SH 6 and 18,000 travel I-40 on average per day. That number for SH 6 is expected to grow to nearly 11,000 by 2040, while average daily traffic on I-40 is projected to be 23,400. Of the traffic that uses I-40, 39 percent is trucks. This is one of the reasons that ODOT decided the DDI was right for the area.

“When we were considering the future of the signal, we recognized it was uniquely suited for a DDI,” says Brian Taylor, Chief Engineer for ODOT. “Because of the traffic volume and many left turns – a high percentage of which were trucks – signals were warranted but not in place.”

As a reminder, DDIs aim to eliminate the left turn and give “free-flowing” or simple left and right-hand turns from all directions. Ultimately, they create safer, less congested intersections, give drivers better sight distance at turns, and make pedestrian crossings shorter. 

A key reason why ODOT went with a DDI is because of the enhanced safety they offer. “The DDI will reduce the number of conflict points from 26 to 14,” says Taylor. “If accidents do occur, they will happen at lower speeds therefore lessening the severity of the accidents.” According to Taylor, the area was experiencing some issues previously, but it was not elevated.

Budget and Schedule

The project began in May of 2019 and is expected to be complete by the end of this summer. ODOT and their contractor – Oklahoma’s Frontier Bridge Inc. – are on target to complete the project on time despite getting off to a slow start due to rain.

Cost of construction for the project is $16 million, and is currently on budget. “ODOT created a really good set of plans that ensured we stayed on budget,” says Taylor.

Bidding was done via an optional tie job. “There’s a project [a bridge over the North Fork Red River] similar in nature nearby,” says Taylor, “so we put out the type of bid in the hope we could get economy of scale.” Ultimately, Frontier was indeed awarded both contracts saving ODOT an estimated nearly $2.4 million.

The funds to pay for the project are coming from the Federal, State, and City governments. The project was a recipient of a $1 million accelerated innovation deployment demonstration grant from the Federal Highway Administration. “We received the grant because this is the first DDI in Oklahoma to go to construction,” says Taylor.

Elk City contributed $250,000, which will be used towards the aesthetics of the project. The final project will include bronze elk statues and decorative elements on and around the bridges.

As noted above, there was a significant amount of rain in the area of the project when construction began, and this caused it to get off to a slow start. “Frontier added crews to make up for the lost time,” says Taylor, “which made it possible to have the project complete this summer.”

Because I-40 and SH 6 are highly trafficked, the project had to be built in phases. Removal of the old bridges and construction of the new bridges was done half at time. Multiple phases helped to keep traffic moving and also maintained full access to all the adjacent businesses. Those businesses include truck stops and other common businesses found around interstates.

While Elk City has been supportive and excited about the DDI from the beginning, informing them of the new traffic pattern is necessary. “It’s an educational process, and we will be working with city and local officials to help educate the traveling public as to what is to be expected,” says Taylor.

When drivers go into a DDI for the first time, many know it’s different, but do not realize they are driving on a different side of a road. “A DDI prevents you from making mistakes, so we don’t anticipate problems,” says Taylor.

With the completion of the Elk City DDI, there will be an increase in safety and capacity leading to lessening of delays. Although Route 66 is no further in its current form, a smooth ride through Western Oklahoma persists.