‘Flex lanes’ aid traffic flow — and are proving safe
By Lee Davidson | The Salt Lake TribuneFirst published Jul 08 2013 01:01AM
New reversible "flex lanes" on 5400 South in Taylorsville — where some lanes go one direction in the morning and the opposite way in the afternoon — are carrying more traffic more quickly than before the conversion. And to the surprise of many, they haven’t increased crashes.
"We get calls from people who say they won’t drive there anymore because it scares them or they feel it is dangerous. But the data show something different," says Utah Department of Transportation spokesman Adan Carrillo.
For a 1.9-mile stretch between 1900 West and Bangerter Highway, the road has four lanes of traffic in the direction of heavy commuting at peak times and two in the other direction — plus a turning lane. At off-peak times, it allows three lanes in each direction. They are the state’s first reversible lanes, built to avoid widening the road and demolishing many businesses and homes.
Travel data • A UDOT-commissioned study by Avenue Consultants shows that in peak directions, the road is carrying 17 percent to 21 percent more traffic — depending on the time of day and where traffic is measured. That amounts to 290 to 380 extra cars per hour.
While carrying that extra traffic — some of it apparently switching over from busy 4700 South — the study said afternoon peak-direction travel times were reduced by 50 seconds — thanks to the extra lane. Travel time dropped by 45 seconds during the morning commute.
Meanwhile, in the off-peak direction, traffic volume remained essentially the same, depending on the spot measured.
Afternoon off-peak travel times were reduced by 20 seconds — even though a lane was lost in that direction. But morning off-peak travel times increased by 65 seconds.
The study said the benefits of shorter travel times in peak directions with higher volume "outweigh the detriments of the increased travel time in the a.m. nonpeak direction."
Information for the study was collected in April and compared to travel data for May 2012. The flex lanes were activated in November.
Accidents • While rush-hour commutes have been eased a bit, safety concerns voiced when the new system came on line haven’t materialized, according to preliminary data provided by UDOT and the Unified Police Department.
From the time the lanes were activated in November through May, UPD numbers show 34 accidents in the flex-lane area. That is down from 54, 53 and 77 during the same period and place during the three preceding years, according to UDOT data.
Robert Miles, UDOT traffic operations engineer, cautions that data for the most recent period are considered preliminary and not verified. He also noted that accident information sometimes is not put into databases immediately by police.
"I’m not willing to say at this point that flex lanes made it safer," Miles said. "But it [the information] tells me we haven’t made it worse."
The preliminary data did not include whether any of the 34 accidents reported were head-on, although Miles said UDOT was not aware of any fatalities on the stretch. In the three years before conversion to flex lanes, that stretch of road had five head-on collisions, 54 crashes with injuries but no fatalities in similar November-May periods that were examined.
Unified police Lt. Justin Hoyal said because the numbers at first looked surprisingly low, he had his department run them again a little differently — between Redwood Road and Bangerter [where cars could be confused as they approach flex lanes] for January through June comparing 2012 and 2013.
In 2012, that area had 122 accidents, compared with 101 this year (although not all accidents in June may yet have been counted).
"Even with these flex lanes, the number of crashes are about the same or less," Hoyal said.
Miles said another measure that suggests accidents are not out of line in the flex-lane stretch is comparing accidents there to other parts of 5400 South.
For November through May, the flex-lane area had 17.9 accidents per mile. Other portions of 5400 South between 1400 West and State Road 111 (at the base of the Oquirrh Mountains) had 21.6 accidents per mile.
"Statistically," Miles said, "there’s not a higher percentage of traffic accidents happening per length of roadway" in the flex-lane section.
Dangers • But Jason Jo, manager of a 7-Eleven at the corner of 3200 West and 5400 South, said he sees plenty of close calls.
"People who use it every day understand it. But people who are new to it don’t," he said. "Some stop and wonder if they are in the right lane and get hit from behind."
One problem, he said, is that at intersections, turn lights and explanatory signs are not exactly over the lanes they affect — but overhead gantries do have lane-control lights exactly over lanes affected. Jo said the difference seems to cause drivers to stop because they wonder if they are in a correct lane.
Hoyal says motorists do need "to be just be a little more alert as they are driving through the area."
Miles said UDOT will continue to closely monitor the performance of the flex lanes.
"We’re still learning more about where [else] we can apply this concept and be successful. We’ve definitely learned a lot with this one."
One lesson was learned soon after the new system was activated when UDOT realized it had installed too many control lights too close to one another on overhead gantries.
When the section opened, some drivers complained that there were so many red, green and yellow lane-control lights — every 500 feet — that some had trouble discerning regular intersection signals and unwittingly ran red lights or slammed on brakes at the last moment.
So UDOT turned off, and later removed, the two outside lane-control lights, where traffic never reverses anyway, just before and after each intersection to help traffic signals stand out more.
The overhead gantries have green arrows in lanes where traffic is allowed, red X’s where it is not, yellow X’s where traffic should begin moving out of lanes because directions are about to change, and yellow left-turn markers for the middle turn lane.