Objective

Today’s transportation professionals, with limited 

resources available to them, are challenged to 

meet the mobility needs of an increasing population. At many highway junctions, congestion continues to worsen, and drivers, pedestrians, and bicyclists experience increasing delays and heightened 

exposure to risk. Today’s traffic volumes and travel 

demands often lead to safety problems that are too 

complex for conventional interchange designs to 

properly handle. Consequently, more engineers are 

considering various innovative treatments as they 

seek solutions to these complex problems. 

The corresponding technical report, Alternative 

Intersections/Interchanges: Informational Report 

(AIIR) (FHWA-HRT-09-060), covers four intersection designs and two interchange designs that offer 

substantial advantages over conventional at-grade 

intersections and grade-separated diamond interchanges. The AIIR provides information on each 

alternative treatment covering salient geometric design features, operational and safety issues, 

access management, costs, construction sequencing, environmental benefits, and applicability. This 

TechBrief summarizes information on one of these 

alternative interchange designs—the displaced leftturn (DLT) interchange (see figure 1). In the figure, 

Research, Development, and Technology Turner-Fairbank Highway Research Center 300 Georgetown Pike, McLean, VA 22101-2296

www.tfhrc.gov

TECHBRIEF

FHWA Publication No.: FHWA-HRT-09-056

FHWA Contact: Joe Bared, HRDS-05, (202) 493-3314, joe.bared@dot.gov

This document is a technical summary of the Federal Highway Administration 

report, Alternative Intersections/Interchanges: Information Report (AIIR)

(FHWA-HRT-09-060).

Displaced Left-Turn Interchange

Figure 1. Typical DLT interchange movements.
2

the red circle indicates a signal-controlled crossover; the purple circle indicates a signal-controlled 

main intersection; the orange arrows indicate 

vehicular crossover movement; and the yellow 

arrow indicates opposing through movement at 

the signal-controlled crossover.

Introduction

The DLT interchange is a new interchange design 

that has similarities to both the at-grade DLT intersection and the double crossover diamond (DCD) 

interchange. The main feature of the DLT interchange is that left-turning traffic crosses over the 

opposing through lanes several hundred feet 

upstream of the main intersection and then proceeds on a new roadway situated between the 

opposing through lanes and a roadway that 

carries right-turning traffic from the ramp. From 

this new roadway, the left-turn traffic completes 

its maneuver onto the on-ramp. 

A DLT interchange has four signalized junctions: 

two at the crossovers for the DLT movements 

and two at the ramp terminals of the interchange. The DLT interchange design reduces the 

number of phases at the signal-controlled ramp 

terminals within the interchange from three to 

two, thereby reducing delays to drivers, pedestrians, and bicyclists as they pass through the 

interchange area. To ensure the smooth progression of traffic, all four signalized junctions are 

operated in a coordinated system. A DLT interchange has the same number of conflict points 

as a conventional diamond interchange. However, 

fewer angle crashes may be anticipated in a DLT 

interchange compared with a conventional interchange because conflicts are more separated.

Geometric Design

The primary design elements of a DLT interchange 

(see figure 2) are as follows:

•	 Left-turning traffic is displaced from the main 

intersection by adding lanes that allow traffic 

to cross the opposing through traffic at a 

signal-controlled location 400 to 500 ft 

upstream of the main intersection.

•	 Radii of the crossover movements range 

from 150 to 200 ft, and radii of the left-turning 

movement at the interchange nodes depend 

on the turning path of the selected design 

vehicle (see figure 3).

•	 A larger overall interchange footprint may be 

needed, given that major road left-turning 

vehicles travel on the opposite side of the 

roadway, requiring a wider median.

•	 U-turn movements on the arterial roads are 

prohibited in the interchange area, similar to 

the DLT intersection.

•	 Access to adjacent properties is limited by

the interchange design, and accommodation 

of individual driveways is considered on a 

case-by-case basis.

•	 Pedestrians can be accommodated in a DLT 

interchange as shown in figure 4.

Figure 2. Typical DLT interchange geometry.

R 30

R 30
3

Traffic Signal Control

A DLT interchange typically has traffic signals at 

each of the two left-turn crossovers and at each 

of the two ramp intersections. Signal control at 

each of these four junctions operate with just two 

phases for the alternative conflicting movements 

and are coordinated to maintain progression on 

the arterial road. Traffic signals at a DLT interchange 

are fully actuated to minimize delay.

Operational Performance

The traffic simulation software VISSIM was used 

to compare the operational performance of a DLT 

interchange design to a conventional diamond 

interchange design. Two geometric design cases 

of DLT and conventional interchanges were simulated using variations of traffic flow scenarios. 

Some of the important results of the analysis were 

as follows:

•	 A 10- to 22-percent reduction in interchange 

delays compared to conventional diamond 

interchanges.

•	 A 10- to 15-percent increase in vehicular 

throughput compared to conventional diamond interchanges.

Safety Performance

Without any known installations, empirical data on 

the safety of DLT interchanges is currently unavailable. The DLT interchange and the conventional 

interchange both have 26 conflict points. However, 

the DLT interchange may result in fewer crashes 

because conflict points are more separated. 

Applicability

The DLT interchange design should be considered 

in situations where the following conditions are 

present: 

•	 Heavy and balanced through volumes on the 

arterial roadway.

•	 Moderate to heavy left-turn volumes from the 

arterial to the on-ramp.

•	 Low to moderate left-turn volumes from the 

off-ramp to the arterial.

•	 Limited bridge deck width, but right-of-way is 

available on the bridge approaches.

Figure 3. Left-turn crossover movement in a DLT interchange.

60’

60’

Tracking Vehicle 

(WB-67)

Tracking Vehicle 

(Passenger Car)

R 160’ R 145’
4

Researchers—This study was performed by Principal Investigators Warren Hughes and 

Ram Jagannathan. For more information about this research, contact Joe Bared, FHWA Project 

Manager, HRDS-05 at (202) 493-3314, joe.bared@dot.gov.

Distribution—This TechBrief is being distributed according to a standard distribution. Direct distribution is being made to the Divisions and Resource Center.

Availability—This TechBrief may be obtained from the FHWA Product Distribution Center by 

e-mail to report.center@dot.gov, fax to (814) 239-2156, phone to (814) 239-1160, or online at 

http://www.tfhrc.gov/safety.

Key Words—Displaced left-turn interchange, DLT, Continuous flow interchange, CFI, and Alternative 

interchange.

Notice—This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no liability for 

the use of the information contained in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they 

are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides highquality information to serve the Government, industry, and public in a manner that promotes public 

understanding. Standards and policies are used to ensure and maximize the quality, objectivity, 

utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its 

programs and processes to ensure continuous quality improvement.

october 2009 FHWA-HRT-09-056

HRDS-05/10-09(3M)E

Summary

The DLT interchange offers benefits over a conventional diamond interchange with its efficient 

and simplified two-phase operation resulting in

expected increased capacity, reduced delay, and 

separated conflict points. At the time of this 

report, there were no known implementations 

of DLT interchanges. More details can be found 

in the full AIIR report available from the Federal 

Highway Administration.

Figure 4. Pedestrian accommodation in a DLT interchange.