CDOT Changes Left-Turn Arrow Signal Phasing at US 160/550 and Sawyer

April 27, 2015 - Southwestern Colorado/CDOT Region 5 - Durango Fire called attention to increase injury accidents.

DURANGO – Earlier today, the Colorado Department of Transportation (CDOT) changed the left-turn signal phasing at US 160/550 and Sawyer Drive. This change is a result of communications with the Durango Fire Protection District.

“By analyzing our response data, staff noticed an increase in injury transports from accidents at the Sawyer intersection,” DFPD Fire Marshall Korola Hanks said. “We then discussed our data with CDOT and traffic engineers responded with an analysis of accident data at this intersection, as well as adjacent intersections.”

All accidents that generate a report from Colorado State Patrol, county sheriff, or police departments are entered into a statewide database. CDOT is able to run reports from this database. CDOT traffic engineers in Durango called up the following in the database to look at any apparent issues with left-turning movements at the signals. The following data were reviewed:

  1. Injury and fatality accidents only (not those that caused only property damage to the vehicle)
  2. Collisions that were caused by left-turning motorists (not by those making the through movement)
  3. 2.5 years BEFORE the installation of flashing yellow arrows (FLA) and signal timing project of 2011 and 2.5 years AFTER the project

From US 160/US 550 Continuous Flow Intersection (CFI) to SH 172 (the high-speed signals in Durango)

BEFORE  64*                    AFTER 50**            REDUCTION OF 14
* Of the 64 injury accidents along the CFI to SH 172 stretch before the installation of FYAs, 26 were due to rear ending, 26 were due to improper left-turn movements, and 12 had other causes.
**Of the 50 injury accidents along the CFI to SH 172 stretch before the installation of FYAs, 23 were rear end accidents, 17 were left-turn accidents and 10 were other causes.

On US 160/US 550 from Continuous Flow Intersection (CFI) to SH 172
*These are collisions caused by a left-turning driver’s failure to yield to oncoming traffic during a flashing yellow arrow, a failure to yield during the signal transition from a steady yellow to red arrow, or running a red arrow.

BEFORE 26             AFTER 17               DDECREASE OF 9

At US 160/550 and Sawyer Drive (nearly all collisions here occurred during weekday midday)

BEFORE 4               AFTER 8                 INCREASE OF 4


County Road 210      BEFORE 3               AFTER 2                 DECREASE OF 1

Dominguez Drive      BEFORE 6               AFTER 0                 DECREASE OF 6

River Road                BEFORE 5             AFTER 1*               DECREASE OF 4
*This collision occurred when a left-turning vehicle ran a red arrow.

“The data show we have good reductions in the amount of serious accidents, overall,” CDOT Region 5 Traffic Engineer Mike McVaugh said. “We’ve significantly reduced the number of injury accidents throughout the high-speed corridor, even with the increasing traffic volumes—this is extremely positive. However, as Sawyer indicates, not all locations saw a decrease in injury accidents.” 

Thousands of left turns are made each day at Durango intersections on the “permissive” flashing yellow arrows (and green circular ball on the old 5-section signal heads that are still in use at some intersections). According to left-turn signal phasing guidelines, during midday weekdays in Durango (when most of these left-turning collisions at Sawyer occurred), there are sufficient gaps in traffic to enable drivers to make safe left turns. But due to the increase in injury accidents at Sawyer, the weekday midday timing plan now runs with “protected only” left-turning. In other words, drivers wanting to turn left onto Sawyer from either direction now have only the “protected” green arrow; there will be no more “permissive” flashing yellow arrow phase, giving them an option to turn at their discretion. Flashing yellow arrows at Sawyer will remain in use during nighttime and possibly weekends, since these periods of the day did not have an accident history.

The data on collisions along this corridor also showed that drivers are still running red lights, on both red through movements and on red arrows. CDOT notes drivers are also taking chances on yellow.

“One of the primary causes of collisions we’re seeing—and this was also the case prior to the flashing yellow arrows—is that motorists are not waiting to initiate their turn when there is a safe gap in traffic,” McVaugh said. “Instead, they creep out into the intersection and risk a quick left turn on a solid yellow, assuming oncoming traffic is stopping. If oncoming traffic does not stop, this can lead to serious injury collisions.”

All left-turning vehicles, at signalized or un-signalized locations, are required to yield to oncoming traffic unless they have a green arrow signal. Any flashing yellow light, whether on a signal head or on any warning sign (wildlife crossing, reduced speed ahead, etc.) informs a motorist to use caution.

“The left-turn flashing yellow arrow is a cautionary indication—it is displayed whenever the opposing direction has a through-green signal,” McVaugh said. “Traffic signals rely almost exclusively on voluntary compliance by drivers.”

CDOT’s summer signal timing plans for the US 160/550 corridor through town—from SH 172 through Animas View Drive—will go into effect over the next month. Signal timing alternates between winter and summer plans to better correspond to the differences in traffic volumes between the seasons.

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