Photo by Zane Znamenacek, CDOT (used with permission).

FHWA-SA-09-016

This case study is one in a series documenting successful 

intersection safety treatments and the crash reductions that 

were experienced. Traffic engineers and other transportation 

professionals can use the information contained in this case 

study to answer the following questions:

•	 What isan innovativetreatmentoption toreduceinjuryandanglecrashesat

T-intersections in ruralareas?

•	 How manycrashesdidthis treatment reduce?

•	 Arethereanyimplementation issuesassociated with this treatment

and, if so, how can theybeovercome?

Continuous Green

T-Intersections

Intersection Safety Case Study
2 FHWA | Continuous Green T-Intersections

Treatment Summary

Both of the intersections complied with 

minimum Manual on Uniform Traffic 

Control Devices (MUTCD) requirements 

before improvements. The CDOT 

converted both of these fully-signalized 

intersections to CGTs. 

The CGT design allows main line through 

traffic to pass through a signalized 

intersection without stopping (the top 

side of the “T”), while also eliminating 

conflicting vehicular movement. With 

a CGT, the through movement on the 

main line approach to the intersection is 

denoted by a steady green arrow traffic 

signal as well as by pavement markings 

or other lane delineation devices, so leftturning traffic stays in its respective lane 

(CDOT implemented advance warning 

signs to inform drivers of the special lane 

configuration). Engineers should only 

consider the CGT at intersections with 

three approaches, moderate-to-low leftturn volumes from the cross-street, and 

high arterial through volumes. 

Objective

The following case study showcases two rural intersections in Colorado where the signal-controlled through lane 

on the flat side (top) of a T-intersection was converted to a CGT. The treatment was implemented to reduce angle 

crashes due to left-turning traffic on the stem, turning in front of the though movement on the top of the T (Figure 1 

provides a photograph of one of the intersections).

Introduction

Angle crashes are among the most severe crashes that occur in intersections, including 

T-intersections. In some cases, substandard sight distance can contribute to this problem. 

Several States including Colorado, Florida, Maryland, North Carolina, and South Carolina have 

converted from fully-signalized to continuous green T-intersections (CGT) to improve safety.

Figure 1: Aerial view of the CGT in Grand Junction, Colorado

Source: CDOT

T-intersection “stem”

Main line (“Flat” side (top) 

of the T-intersection) with 

continuous green signal

Dedicated left-turn lane 

from stem extends to main 

line to enhance safety

Photo from Zane Znamenacek, CDOT (used with permission).
“Based on the operational 

and crash analysis conducted, 

it was concluded that road 

designs such as CGTs offer 

a substantial improvement 

in safety as well as volume 

of throughput. Public 

acceptance was very high 

and it is one of those 

treatments that the traveling 

public agrees ‘makes sense’.”

Zane Znamenacek 

Traffic Engineer 

Colorado Department

of Transportation (CDOT)

FHWA | Continuous Green T-Intersections 3

Photo by ATTAP, University of Maryland-College Park (used with permission).

EB US-50
4 FHWA | Continuous Green T-Intersections

The safety enhancements discussed in this case 

study were added to reduce angle, injury and total 

crashes. Implementation of the CGT cumulatively 

reduced angle crashes at the treated intersections 

by 96.8 percent, injury crashes by 70 percent, and 

total crashes by 60 percent.

Photo by Zane Znamenacek, CDOT (used with permission).
FHWA | Continuous Green T-Intersections 5

Results

Problem: Two T-intersections in Grand Junction and Durango, CO were experiencing a high incidence of crashes, 

particularly angle crashes and many with injuries, due to limited stopping sight distance. 

Solution: CDOT sought an intersection design treatment that would eliminate the stopping sight distance problem and to 

reduce the number of angle crashes, while also improving the efficiency of these intersections: 

•	 US-50 and SH 141, Grand Junction, CO

This rural intersection serves an annual daily traffic (ADT) of approximately 16,800. Prior to conversion, the east-west highway (US-50) 

had two lanes in each direction and a posted speed limit of 45 miles per hour (mph). The north-south highway

(SH-141) had one lane in each direction and a speed limit of 35 mph. 

In 2004, the traffic control on eastbound (EB) US-50 was converted from a fully-signalized intersection to a CGT to eliminate the 

substandard sight distance problem and thus reduce the number of injury and angle crashes. The two right lanes were designed to 

carry continuous through traffic while a separate left-turn deceleration lane was provided for exclusive left-turning movement onto 

SH-141 (the mainline). Similarly an acceleration lane was provided from SH-141 onto EB US-50 (the stem of the T-intersection). The 

acceleration and deceleration lanes were channelized, and pavement markings and a 4-foot-wide concrete median separated the 

continuous through lanes. Appendix A provides plan details for this intersection.

After the conversion of this intersection to a CGT, angle crashes decreased from 16 to 0 (a 100 percent reduction); injury crashes 

decreased from 12 to 2 (an 83.3 percent reduction); total crashes decreased from 16 to 7 (a 56.3 percent reduction).

•	 US-160 and US-550, Durango, CO2

This rural intersection serves an ADT count of approximately 30,000. Both the east-west highway (US-160) and the north-south 

highway (US-550) had a posted speed limit of 50 mph. 

The traffic control at the intersection of westbound 

(WB) US-160 and US-550 was converted to a CGT in 

1996 (see Figure 2) to reduce the number of injury and 

angle crashes. 

After conversion, US-160 (the main line) had a single 

through lane running WB with a separate deceleration 

lane; and two lanes running EB. US-550 (the stem of 

the T-intersection) had one acceleration lane for WB 

movement. Pavement markings and a 4-ft-wide median 

separated the continuous through lane and the adjacent 

left turning lane. 

After the CGT conversion, angle crashes decreased 

from 15 (including 1 fatality) to 1 (an average crash 

reduction of 93.3 percent); injury crashes decreased 

from 8 to 4 (an average crash reduction of 50 percent); 

and total crashes decreased from 19 to 7 (an average 

crash reduction of 63.2 percent).

Evaluation Methodology

This case study examines two rural T-intersections in Colorado, with a high incidence of injury and angle crashes. Crash 

reduction results were based on a review of “before and after” data from these intersections during a period of four years, 

which occurred during the period between 1994 – 20061. (The “before” and “after” observation periods were 24 months at 

both intersections).

Figure 2: WB on US-160

1 Note that reduction averages in this report reflect the percent reduction per year based on the difference between the total number of “before” and “after” crashes.

2 Plan details for this intersection were not available.

Photo from David Pickren, CDOT (used with permission).
6 FHWA | Continuous Green T-Intersections Months

Total 

Crashes

Injury 

Crashes

Months

Total 

Crashes

Total 

Crashes

Injury 

Crashes

Injury 

Crashes

Angle 

Crashes

Angle 

Crashes

Angle 

Crashes

Location Implementation

Date

Before After Reduction In Crashes/Year

US-50 and 

SH-141 

US-160 and 

US-550 

Apr-02

Aug-96 

Total

24 16 12 16 24 7 2 0 56.3% 83.3% 100% 

24 19 8 15 24 7 4 1

(1 fatality) 

63.2% 50% 93.3% 

48 35 20 31 48 14 6 1 60% 70% 96.8% 

Table 1: Summary of crash reductions after conversion to CGT.

Data Source: CDOT

Discussion

Implementation Issues

CDOT experienced no implementation issues 

converting these intersections to CGTs. However, the 

major movement of the side streets (the minor routes 

on the “stems” of the T-intersections) was affected by the 

lane closures required for maintenance of these CGTs, 

as there were no reasonable alternate routes. Also, the 

geometric changes (i.e., lane construction) required 

more time and approvals than operational changes (i.e., 

traffic signal timing adjustments).

Cost

The construction cost of the CGT, which included the 

new signal as well as the raised median work, was 

approximately $300,000 for each intersection.

Time Frame

The CGT was implemented within three months at each 

intersection.

Effectiveness 

The CGTs were effective in substantially reducing angle, 

injury and total crashes at these intersections. 

Summary of Results 

The safety enhancements discussed in this case study 

were added to reduce angle, injury and total crashes.

Implementation of the CGT cumulatively reduced 

angle crashes at the treated intersections by 96.8 

percent, injury crashes by 70 percent, and total 

crashes by 60 percent.

References

1) Jarem, E.S., “Safety and Operational Characteristics 

of Continuous Green Through Lanes at Signalized 

Intersections in Florida,” Presented at the 2004

Institute of Transportation Engineers (ITE) Annual 

Meeting and Exhibit. 

2) Boone, J.L., and Hummer, J.E., Unconventional 

Design and Operation Strategies for Oversaturated 

major Suburban arterials: Final Report, Project 

23241-93-9, North Carolina State University, 

Department of Civil Engineering, Center for 

Transportation Engineering Studies, April 1995.

3) Reid, Jonathan, “Unconventional arterial 

intersection design, management and operations 

strategies,” Parsons Brinckerhoff, July 2004.

Table 1 summarizes the results of the “before” and “after” crash analysis at the treated intersections.
FHWA | Continuous Green T-Intersections 7

Appendix A: US-50 and SH-141 Plan Details
FHWA-SA-09-016 February 2010

For More Information

Ed Rice

Intersection Safety Team Leader, 

FHWA Office of Safety

202.366.9064

ed.rice@dot.gov

Zane Znamenacek

Region 3 Traffic Operations Engineer, 

Colorado Department of Transportation (CDOT)

970.683.6278

zane.znamenacek@dot.state.co.us