The Seattle Department of Transportation (SDOT) today released its before and after study of the Stone Way N. rechannelization, which the department said demonstrates that Seattle’s streets can be made safer through lane reconfigurations.
The report documents that the lane changes on Stone Way N. from 34th St. to 50th St. have had the effect of reduced speeds for motorists and fewer motor and bicycle collisions - while still maintaining the road’s capacity.
Highlights from the study include:
• Motor vehicles now travel at speeds nearer the legal limit;
• Total collisions dropped 14 percent with injury collisions down 33 percent;
• Pedestrian collisions declined significantly;
• Bike trips increased 35 percent but collisions per bicycle trip have declined; and
• Volumes show the roadway still easily accommodates motor vehicle traffic.
Data collected by SDOT on the rechannelized street shows motorists drive at speeds closer to the posted 30 m.p.h. limit and a decline of more than 80 percent in those traveling over 40 m.p.h. The study also reveals a decrease in total collisions by 14 percent and pedestrian collisions by 80 percent.
The study compared the before period (April 2005-August 2007) to a period after the rechannelization (August 2007-December 2009.) SDOT converted the street to two general travel lanes with a center turn lane from N. 40th to N. 50th streets in August 2007 and from N. 34th to N. 40th streets in April 2008. Additional bike and pedestrian facilities were also installed at those times. Before the lane reduction, the street consisted of four general purpose travel lanes.
National studies show that lane reductions can result in lower motor vehicle speeds, improved pedestrian safety, increased bicycling trips and fewer collisions, while maintaining a corridor’s capacity. Starting in 1972 with California Ave. SW and N. 45th St, the city of Seattle has implemented 24 rechannelizations as of April 2010.
There was one interesting increase, buried at the end of the study:
The number of rear‐end collisions increased, especially between N. 39th St. and N. 41st St. This type of collision increased 65% during the study period (from 17 to 28) in spite of the overall reduction in the number of collisions. Since most of the increase was attributable to the
section of roadway where there was a transition from 4 lanes to 3 lanes during the interim
period between August 2007 and April 2008, one possible explanation is that drivers had
difficulty making left turns in this transition area. While these types of collisions tend to be
minor in nature, SDOT will again examine the rate of rear‐end collisions within the next two
years to determine if the rate in fact declined after the roadway was rechannelized south of
40th Street.
For more information: check out SDOT’s website.
8 responses so far ↓
1 C W // May 26, 2010 at 12:51 pm
Time and time again what these studies fail to account for is what happens on the alternate routes when these diets are put into place. I’m not saying these diets are all/always bad, but unless a complete picture is analyzed, it’s hard to tell if overall safety has improved, or just safety in a specific location.
2 Peter // May 26, 2010 at 1:27 pm
Is it fair to call this a “diet” when the study shows that overall capacity was maintained?
If Stone Way has the same number of trips but trips on side roads increase, then it doesn’t seem clear to me at all that there is any causal relationship.
(If I’m biased in defence of this project, it’s because I like the improvements and would rather make left turns from a center lane over two lanes any day.)
3 T O // May 26, 2010 at 1:52 pm
This story is more notable for what it does not report, which is the total traffic volume numbers, or the number of collisions per car trip on Stone way in the before and after periods. These would give a better indication of whether the traffic has just been pushed into other surrounding neighborhoods. Interesting that the story seems slanted to reach a particular conclusion rather than just reporting news.
I, for one, do not use this stretch of road or frequent the businesses there any more due to the increased congestion and increased time it takes to get through the corridor.
4 Tom Sparks // May 26, 2010 at 2:02 pm
My personal experience has been these changes on Stoneway have led to a safer, calmer and friendlier street. I still use Stoneway and support businesses there.
I know Nickerson along the ship canal is next for this kind of mediation. Nickerson will be much more interesting since the backups from the Fremont Bridge can be terrible.
5 motorrad // May 27, 2010 at 11:36 am
These studies fudge the overall volume. Anyone that believes you can force 2 lanes of traffic volume down to one lane and that the volume will stay the same is ripe for other con men. The traffic is going elsewhere like the residential streets.
6 MichaelSnyder // May 27, 2010 at 6:15 pm
mortorrad,
There wasn’t enough volume there in the first place to justify 4 lanes and if memory serves from when I sat there counting traffic movements, 10-20% of the traffic was turning left (across two oncoming lanes while blocking their own lane). By converting this to two through lanes and a center turn lane, traffic flows much easier now.
If there was enough traffic to require all four lanes, something like 58,000 AAWDT sees, then sure, the road diet would possibly reduce overall volume…but then again a quote on the Seattle Transit Blog recently pointed out that in the Netherlands a traffic engineer noticed that the number of cars stayed the same between 20 mph and 40 mph…they were just spaced closer together at 20 mph and spread futher out at 40 mph.
7 Mark // May 28, 2010 at 2:45 pm
I live on 36th and Woodland Park (one block off of Stone). I’m not sure what traffic on this street was like before the change but I know now that we have a lot of people speeding down a three block stretch to get between Fremont Ave. and Bridge Way.
8 Trouble Maker // May 30, 2010 at 12:45 pm
The diet seems to have leveled the playing field a bit.
The 2 ton vehicles are playing bumper cars with each other, instaed of cyclists and pedestrians, to squeeze into the reduced number of lanes.
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