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Interstate 15 and Timpanogos Highway, Lehi, UT 

DIVERGING DIAMOND INTERCHANGE 

THE PROBLEM 

The area experienced 

increasing population growth 

and traffic demand, leading

to backups and delays at the 

interchange. Alternatives 

to reduce congestion had to 

minimize the footprint of the

I 15 bridge over the crossroad 

and keep the interchange 

within the existing right of way.

THE SOLUTION 

Installation of a DDI 

constructed under the 

highway overpass. 

THE OUTCOME 

Q Studies show that the 

renovated infrastructure 

has resulted in an influx of 

over 100 new business and 

4,000 new jobs.3 

Q The DDI design allowed 

UDOT to easily add two 

signalized crosswalks, 

providing safer and more 

convenient pedestrian 

facilities.

Q The DDI design also 

integrated provisions 

for bicycles, including a 

shared use path and wide 

shoulders. 

CONTACT 

Jeffrey Shaw, P.E.

FHWA Office of Safety

202.738.7793

jeffrey.shaw@dot.gov

Mark Doctor, P.E.

FHWA Resource Center 

404.895.6210

mark.doctor@dot.gov

INTERCHANGE LOCATION 

40°25’53.0”N 111°53’26.7”W 

“

”

We’re ... happy to see [the 

interchange] serving many 

users— bicyclists, pedestrians, 

cars, and heavy [hauler] traffic.

Background 

Located at the interchange of Interstate 15 and 

Timpanogos Highway, or State Route 92, the new 

Diverging Diamond Interchange (DDI) was part of 

a highway expansion project intended to increase 

throughput and accommodate expected future 

growth. Before construction of the new DDI, traffic

moved through a conventional diamond interchange. Increasing commercial and population 

growth created a surge in demand on the local road and interchange. Before long, the limitations of the conventional design became apparent in delays and backups. 

— Daniel Avila, P.E. 

Deputy Program Director, Access Utah County, Utah DOT 

Challenges 

Timpanogos Highway runs below 

I-15. UDOT wanted to maintain the 

existing I-15 bridge deck, keep the 

new interchange within the area 

of the existing roadway, and minimize the footprint that I-15 would 

need to span.1

 In addition, the new 

interchange would need to include 

pedestrian and bicycle facilities, 

features that were absent in the 

original interchange. 

View of the Intersection of I-15 and Timpanogos Highway, Lehi, UT 

Source: DDI Case Study Video FHWA-SA-14-045 

Approach 

With the DDI located below the highway overpass, UDOT met its construction challenges by 

using existing asphalt and eliminating the need for extensive renovations to the I-15 bridge. This 

design also allowed UDOT to retrofit two signals to provide for pedestrian and bicyclist crossings.

Results 

With its improved traffic flow and accessibility 

to foot and bicycle traffic, studies credit the 

new interchange with an influx of over 100 

new business and 4,000 new jobs.2 In addition, the DDI has made travel more efficient 

and accessible for all users. 

Pedestrian Crossing at the DDI Interchange 

Source: DDI Case Study Video FHWA-SA-14-045 

1 Interview with Smith Siromaskul, St. Louis, MO, November 2, 2013. 

2 Lee Davidson, “Two years late, SR-92 expansion finally nears end,” The Salt Lake City Tribune, 

(August 21, 2013) Available at: http://www.sltrib.com/sltrib/politics/56759544-90/udotproject-adams-road.html.csp 

3 Ibid.

www.safety.fhwa.dot.gov

FHWA-SA-14-046 Revised July 2020 This Fact Sheet is a companion to the Video Case Study (FHWA-SA-14 -045)