Advanced Dilemma-Zone 

Detection System

Purpose

The Advanced Dilemma-Zone Detection system enhances safety at signalized intersections 

by modifying traffic control signal timing to reduce the number of drivers that may have 

difficulty deciding whether to stop or proceed during a yellow phase. This may reduce rearend crashes associated with unsafe stopping and angle crashes due to illegally continuing 

into the intersection during the red phase.

Alternative Names

Detection-Control System (D-CS), Intelligent Detection-Control System.

Operation

• The Advanced Dilemma-Zone Detection system minimizes the number of vehicles the intersection 

traffic control signal system exposes to an intersection-approach dilemma zone. This is accomplished 

by adjusting the start time of the yellow-signal phase either earlier or later, based on observed 

vehicle locations and speeds.

• Advanced Dilemma-Zone Detection is intended to safely control the major-road approaches to 

an isolated signalized intersection without creating excessive delay to minor movements. 

• Advanced Dilemma-Zone Detection uses comprehensive detection equipment to measure vehicle 

speeds and flows. Based on the number of vehicles expected to be in the dilemma zone in the 

immediate future and the number of minor-street vehicles waiting to travel through the intersection, 

the Advanced Dilemma-Zone Detection system attempts to identify when (1) the fewest passenger 

cars will be in the dilemma zone, and (2) no heavy vehicles will be in the dilemma zone. 

• Advanced Dilemma-Zone Detection uses the speed, location, and length of vehicles to calculate 

the location of the dilemma zone relative to both vehicle speeds and the intersection approach 

(i.e., the dilemma zone is dynamic: it occurs farther from the intersection for a faster traveling vehicle 

than it does for a slower vehicle). Based on this calculation, the system then adjusts the start time of 

the yellow phase to coincide with the point when the fewest possible vehicles are in their respective 

projected dilemma zones.

Potential Benefits

The Advanced Dilemma-Zone Detection system has several benefits relative to traditional 

multiple detector systems, which have upstream detection for vehicles in the dilemma zone 

but do not take the speed or size of individual vehicles into account. These benefits include:

• Reducing the frequency of red-light violations;

• Reducing the frequency of crashes associated with the traffic signal phase change (for example, 

rear-end and angle crashes);

• Reducing delay and stop frequency on the major road; and

• Maintaining or reducing overall intersection delay.

This summary is one in a series 

describing Innovative Intersection 

Safety Treatments. The summaries 

identify new technologies and 

techniques to improve intersection 

safety developed since NCHRP 

Report 500, Volumes 5 and 12, 

were published in 2003 and 2004, 

respectively. These treatments 

show promise for improving safety 

but comprehensive effectiveness 

evaluations are not yet available.

May 2009

FHWA-SA-09-008
Agency Experience

• An Advanced Dilemma-Zone Detection system was developed for the Texas Department of 

Transportation (TxDOT) to minimize both delay and crash frequency at rural intersections. 

• This system was implemented as part of a study conducted by TxDOT at several intersections 

using commercially-available equipment in Texas. The evaluation of safety and operational 

benefits found that the system:

- Reduced delay by 14 percent;

- Reduced stop frequency by 9 percent;

- Reduced red-light violations by 58 percent;

- Reduced heavy-vehicle red-light violations by 80 percent; and

- Reduced severe-crash frequency by 39 percent.

FHWA is conducting on-going effectiveness evaluations of the TxDOT study described 

above, and more complete results are expected in the spring of 2010.

Implementation Considerations

• At intersections with currently installed advance detector loops or cameras, it may be possible 

to use the existing detector loops and cameras as part of the Advanced Dilemma-Zone 

Detection implementation.

• Advanced Dilemma-Zone Detection may be most appropriate at high-speed, rural, and 

isolated intersections.

• Advanced Dilemma-Zone Detection systems are currently available as off-the-shelf products 

from some signal controller manufacturers.

Manual on Uniform Traffic Control Devices (MUTCD) Specifications

• There are no compliance issues with the MUTCD, as it does not prescribe detection locations 

for the green phase.

Costs

• Costs vary depending on the extent and type of existing detection infrastructure, but will 

generally be higher then costs associated with traditional detection systems (i.e., systems with 

upstream detection for vehicles in the dilemma zone but which do not take the speed or size 

of individual vehicles into account). Advance loop detectors or video technology, for example, 

can reduce the amount of necessary capital improvements. 

Figure 1: Advanced Dilemma-Zone Detection 

system components as applied in TxDOT 

Detection-Control System study referenced in 

this fact sheet

Learn More

Jim Bonneson, Senior Research Engineer 

 Texas Transportation Institute 

979.845.1713

j-bonneson@tamu.edu

Henry Wickes, Project Director 

 Traffic Operations Division, TxDOT

512.506.5125

hwickes@dot.state.tx.us

Ed Rice, Intersection Safety Team Leader 

FHWA Office of Safety

202.366.9064 

ed.rice@dot.gov

Figure 2: Advanced Dilemma-Zone Detection 

design as applied in TxDOT Detection-Control 

System study referenced in this fact sheet

800 to 1,000 ft 

from stop line

D-CS Detector 

trap

Dilemma zone 

of 70 mph 

vehicle

Dilemma zone 

of 25 mph 

vehicle

Stop line 

detectors

A

B

Detector 

Amplifiers

Signal Head Signal Controller

Vehicle Detection

Industrial 

Personal Computer

(7" x 7" x 10")

Force, 

Hold

Signal

Conflicting Calls

Digital Input/

Output 

Interface

Traffic Control System

Vehicle Detection System

As part of the TxDOT study, the Advanced Dilemma-Zone Detection system was implemented at eight different intersections in Texas. Similar 

systems may have been installed in other locations. Zimmerman, K. and J. Bonneson. “In-Service Evaluation of a Detection-Control System for 

High-Speed Signalized Intersections,” FHWA/TX-05/5-4022-01-1, Federal Highway Administration, 2005. Available at http://tti.tamu.edu/

documents/5-4022-01-1.pdf.