U.S. Department of Transportation

Federal Highway Administration

Federal Transit Administration

1

April 2009

Background

The Denver Regional Council of Governments (DRCOG) 

serves as the metropolitan planning organization for 

the Denver region, home to approximately 2.7 million 

residents in ten counties in north-central Colorado. 

There are now more than 3,500 traffic signals maintained 

and operated by 32 different jurisdictions within the 

Transportation Management Area (TMA). 

In 1989, the traffic signal operating agencies in the Denver 

area concluded that there was a need for interjurisdictional 

timing and coordination of traffic signals. These agencies 

selected DRCOG to develop a regional program because 

DRCOG was viewed as an agency that was regional in 

nature and had the capabilities to facilitate cooperation 

between multiple jurisdictions. DRCOG and the traffic 

signal operating agencies worked together to begin a 

small signal timing and coordination program funded 

by an energy grant. The program provided for one traffic 

engineer to assist in signal timing and coordination in the 

region and no capital improvements. 

The Denver Regional Council of Governments (DRCOG) works with over 30 local jurisdictions on the Traffic Signal System Improvement 

Program (TSSIP), a combination of management and operations strategies designed to time and coordinate traffic signals in the Denver 

region. The program is updated regularly through a collaborative planning process involving representatives from the region’s operating 

agencies. Each agency identifies critical needs yet understands that the focus of the program is improving signals at regionally significant 

arterials. The traffic signal program is identified as one of six action strategies in DRCOG’s 2035 Metro Vision Regional Transportation Plan 

to support the region’s policy of effective management and operations. It serves as a key component of DRCOG’s congestion mitigation 

program and funding is programmed for TSSIP through the transportation improvement program (TIP). The program has already improved 

operations at more than a thousand traffic signals in the region — reducing travel times, fuel consumption, and vehicle emissions. Future 

plans include transit signal priority, expanded signal timing, and development of regional performance measures.

The Denver Region Traffic Signal System

Improvement Program

Planning for Management and Operations

Although the benefits were modest, the first few years 

of the program proved its worth to the region and 

impressed the DRCOG Board of Directors. When the 

Denver region began to receive Congestion Mitigation/

Air Quality (CMAQ) funds due to the adoption of 

the Intermodal Surface Transportation Efficiency Act 

(ISTEA), more funding became available for traffic 

signal improvements. In 1994, the Traffic Signal System 

Improvement Program (TSSIP) was officially adopted and 

an annual budget of $1 million was provided in the TIP. 

How TSSIP Functions

The purpose of TSSIP is to implement cost-effective 

traffic signal timing and coordination improvements that 

reduce travel time and harmful auto emissions within the 

DRCOG TMA. 
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other to implement the projects defined in the program. 

In addition to coordinating TSSIP, DRCOG is responsible 

for conducting timing and coordination tasks on a projectby-project basis for the projects identified in the TSSIP and 

as requested by individual operating agencies. Through these 

tasks, DRCOG identifies corridors to retime, develops and 

fine-tunes timing plans, and documents improvements and 

benefits. In turn, the operating agencies are responsible for 

maintaining and operating their signals, maintaining the 

timing, and reviewing and approving plans. In addition to 

the capital projects that are listed in the TSSIP, the program 

maintains a minor capital improvement contingency fund. 

Annually, operating agencies can apply to compete for these 

funds for the purchase of signal system equipment. The 

operating agencies are responsible for installing any new 

equipment they receive. 

The TSSIP is updated every 3 to 4 years through a 

collaborative planning process involving representatives 

from the region’s operating agencies and was most recently 

updated in 2007. Currently, the budget for the program is 

approximately $3.7 million per year for the period 2008-

2013; DRCOG serves as the facilitator for the program and 

its Board of Directors approves each new proposed program 

update. TSSIP is a set of management and operations 

strategies that are a significant component to DRCOG’s 

congestion mitigation program that also include travel demand 

management and intelligent transportation systems (ITS). The 

traffic signal program is identified as one of six action strategies 

in DRCOG’s 2035 Metro Vision Regional Transportation Plan

to support the region’s policy of management and operations: 

“Make the best use of existing transportation facilities by 

implementing measures that actively manage and integrate 

systems, improve traffic operations and safety, provide accurate 

real-time information, and reduce the demand for singleoccupant motor vehicle travel.” Additionally, DRCOG’s 

regional transportation plan commits funding to TSSIP 

over the long term. CMAQ funding is programmed for the 

combined traffic signal and ITS program in the TIP. 

Currently, there are 32 jurisdictions participating in the 

TSSIP including Adams County, Arapahoe County, 

Boulder County, Douglas County, Jefferson County, 

Arvada, Aurora, Boulder, Broomfield, Brighton, Castle 

Rock, Commerce City, Denver, Englewood, Federal 

Heights, Golden, Greenwood Village, Lafayette, Lakewood, 

Littleton, Longmont, Louisville, Northglenn, Parker, 

Sheridan, Superior, Thornton, Westminster, Wheat Ridge, 

as well as the Colorado Department of Transportation’s 

(DOT) Region 1, Region 4, and Region 6. 

DRCOG approaches this program as a partnership among 

DRCOG and the traffic signal operating agencies. Regular 

program updates are made through a collaborative dialogue 

led by DRCOG, and operating agencies work with each 

Figure 1. The TSSIP is updated every few years. It contains a thorough signal 

system inventory, a description of needs, an implementation schedule, and 

tracks progress. Source: DRCOG.
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Outcomes

Determining and documenting the benefits and 

effectiveness of currently ongoing and programmed projects 

is critical to the TSSIP program. Because the TSSIP is 

funded with Federal CMAQ funds, the benefits of every 

project must be measured and reported.

The TSSIP update process determines which signal needs 

in the region will be addressed through the programmed 

funds. At the onset of the update process, DRCOG invites 

all 32 signal operating agencies to be part of a work group 

and participate in the program. The participant level ranges 

from transportation director to traffic engineer, depending 

on the size of the participant’s agency. 

The process begins with an update of the regional inventory 

of the existing signal system. Information on the type of 

signal control system, number of signals, and hardware 

for each operating agency is recorded into a GIS database 

maintained by DRCOG. After assessing current conditions, 

the working group does a needs assessment. Each agency 

identifies its critical needs with an understanding that 

the focus of the TSSIP is on regionally significant signals 

on main arterials. At the working group meetings, the 

participants develop a list of evaluation criteria for 

prioritizing signal improvement needs. The participants 

evaluate the collective needs based generally on:

•	 Criticality of need.

•	 Importance of the corridor.

•	 Strategic need for the communication link.

•	 Local priorities and synergies.

•	 Cost-effectiveness.

The TSSIP 2007 update is compiled in a written document 

that contains a thorough signal system inventory, a 

description of needs, and an implementation schedule 

of the specific projects to be performed. In addition, the 

document records the progress that has been made in the 

region since the last TSSIP update and it gives data on the 

specific benefits gained from the program.

Figure 2. Map of TSSIP projects completed from June 2003 until the 2007 update. 

Source: DRCOG.
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There are now more than 3,500 traffic signals maintained 

and operated by 32 different jurisdictions within the 

Denver TMA. Nearly 2,600 of these signals are considered 

key signals (signals on principal arterials and major 

regional arterials). In addition, more than 1,940 key 

signals are currently connected to a traffic signal control 

system. All agencies that have key signals and more than 

20 signals to operate have a signal control system.

Since the 2003 TSSIP update, the program has assisted 

16 operating agencies in these upgrade efforts and has 

completed capital improvement projects for 55 arterial 

roadway sections. The program also completed 19 timing 

and coordination projects and 4 traffic responsive control 

projects during the 2003-2008 period. These projects 

improved operations for more than 1,100 traffic signals 

throughout the region and reduced delay by nearly 36,000 

vehicle hours per day, reduced fuel consumption by more 

than 15,000 gallon per day, and reduced air pollution 

emissions (mainly carbon monoxide) by more than 45,000 

pounds per day. Performance results are summarized and 

distributed to the DRCOG Board of Directors so that it 

can use those findings when it makes decisions on how to 

distribute funds across programs. Thus far, the continued 

success of the TSSIP has warranted maintaining its level of 

funding.

Future Directions

During the 2008-2013 period, a number of critical needs 

that have been identified by DRCOG will receive attention. 

These include:

Capital Improvements to Signal Systems

•	 Upgrade and replace insufficient/unreliable

communications for more than 25 corridors 

(330 signals).

•	 Expand the system control to “key signals” not on a

system for more than 12 corridors/areas or projects 

(160 signals).

•	 Improve the efficiency of signal system control in four

jurisdictions.

System Engineering and Design

The TSSIP will fund system studies and design activities 

required for the capital projects identified, as well as 

coordination for regional transportation management and 

ITS planning efforts.

Special Projects

The TSSIP will implement three special projects: transit 

signal priority (continued from efforts begun during the 

previous plan period), Denver Central Business District 

signal timing (more than 200 traffic signals), and the initial 

development of a regional performance measures program 

for traffic signal system operations.
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Timing and Coordination

This fundamental part of the program anticipates continued 

development of new time-of-day (TOD) schedule-based 

timing plans on a recurring basis in a three- to five-year 

cycle or as needed for major corridors and for all capital 

projects implemented (including miscellaneous signal 

equipment purchases). Some additional funds will be 

targeted for selectively developing TOD plans that address 

weekend traffic patterns. Development and evaluation 

of timing plans for traffic responsive control achieved 

successful results in the past few years through trial projects 

and will now be included as they arise.

References

Denver Regional Council of Governments, FAQs. http://

www.drcog.org/index.cfm?page=FAQs. Accessed May 19, 

2009.

Denver Regional Council of Governments, Traffic Signal 

System Improvement Program 2007 Update Summary 

Report, May 16, 2007. http://www.drcog.org/documents/

TSSIP%202007%20Summary%20Report.pdf.

FHWA, Case Studies of Regional Traffic Signal Timing 

Programs. October 2004.

FHWA, Telephone Interview with Steve Cook, DRCOG. 

May 7, 2008.

FHWA, Telephone Interview with Jerry Luor, DRCOG. 

August 15, 2005.

FHWA, Written Interview with Jerry Luor, DRCOG. 

February 2004.

FHWA-HOP-09-046