2 die at dangerous intersection
Rush-hour collision of bus, SUV kills two women; bus driver, 3 students hurt
Friday, October 3, 2008 3:13 AM
By Charlie Boss and Theodore Decker
THE COLUMBUS DISPATCH
A collision yesterday morning that killed two women and injured five others — including three high-school students — occurred at what long has been flagged as one of Columbus’ dangerous intersections.
The design, speed limits and heavy traffic at W. Henderson and Olentangy River roads can spell trouble, area residents and city officials say.
…Mary Carran Webster, the city’s assistant director of public service, said motorists flow to the intersection in part because Henderson Road connects to High Street, unlike nearby Bethel Road. Proposals through the years to link Bethel and Morse roads have been rejected, forcing traffic south to Henderson.
“We’re not likely to get a Bethel connector, and that’s why we’re studying to get a better handle on that traffic to reduce congestion and make it safer,” Webster said.
A joint study with the Ohio Department of Transportation will look at the feasibility of changes to make Henderson and Olentangy River roads handle more traffic, she said.
…The Henderson-Olentangy intersection’s problems aren’t a secret. It was the 32nd-most dangerous in central Ohio, from 2004 through 2006, according to the Mid-Ohio Regional Planning Commission.
Webster said 7,500 vehicles travel through it during morning rush hour and about 50,500 daily. But the number of crashes, mostly rear-end ones, has steadily dropped from 59 in 2003.
After city officials installed brighter traffic lights in 2006, crashes dropped to 35. As of June 21, there had been 21 crashes this year, Webster said.
The stretch of Henderson west of the intersection has a 50-mph limit. East of the intersection is 35 mph, and the road quickly passes under Rt. 315 from there and into a second intersection with a traffic light.
“People come down at 50 miles per hour, trying to make the light and going into the 35,” neighbor Jon Creal said.
I don’t want to comment on the loss of life, which is always a tragedy, or the cause of the crash, which is yet to be determined conclusively. However, I do wonder if anyone else feels that 50 MPH seems a little fast for Henderson Road.
I find that it’s hard to actually get up to 50 MPH, perhaps because I usually drive Henderson going uphill. Nevertheless, I wouldn’t be surprised if the 85th percentile speeds are actually lower than the speed limit, in which case lowering the limit to somewhere between 35 and 45 shouldn’t really be a problem.
A lower speed limit, if obeyed by the majority of drivers, could have several safety benefits.
1. Reduced vehicle stopping distances = fewer rear end collisions
2. Less severe collisions when they do occur
3. Less red-light running due to fewer dilemma zone incidents
I think the first point is somewhat self-obvious. Let’s say you’re heading east on Henderson, like the Nissan Murano in this crash. You see queues ahead and need to brake. It takes 313 feet to comfortably come to a stop from 50 MPH compared to just 169 feet at 35 MPH. A queue just ten cars long is roughly 200 feet. In the 50 MPH scenario, you would have to start braking over 500 feet before you reach the intersection. You have more time to evaluate traffic conditions and brake comfortably if you are traveling slower.
The second point is even more obvious than the first, so I’m skipping to number three. I mentioned the phrase “dilemma zone” in a post on September 20th. A dilemma zone occurs when a motorist traveling at a certain speed can neither stop safely in advance of the intersection nor enter the intersection before a signal changes to red. To avoid a dilemma zone, the amount of yellow time on a signal has to be long enough to make the distance a car would travel during the yellow signal at the speed limit longer than the required stopping distance at that speed. Maybe that’s hard to understand. Let’s use an example.
Imagine a car traveling 50 MPH is exaclty 300 feet from the intersection when the signal changes to yellow. The driver has a choice, go through the intersction or stop. Assume the driver can make that decision in 1.0 seconds. The car traveled 73.3 feet during that reaction time. If the driver decides to stop, he or she needs another 240.0 feet to do so comfortably (according to AASHTO). But that’s a total of 313.3 feet, so the driver has just stopped 13.3 feet into the intersection. Let’s say that the driver decided to go through the yellow light, but the signal is only 4.0 seconds long. At 50 MPH, a car travels 293.3 feet at 4.0 seconds. So the car is 6.7 feet from the intersection when the signal changes to red and the driver runs the red light.
I’m sure the city has the yellow signal on Henderson timed at longer than 4.0 seconds. ITE standards would put the yellow time on a 50 MPH roadway at 4.5 or 5.0 seconds, which would eliminate a dilemma zone if a driver is traveling the speed limit and can react in 1.0 seconds in good weather. BUT, not all drivers travel the speed limit, not all drivers can react in one second, and we don’t live in Phoenix where it’s always sunny. Traffic engineers assume 15% of drivers will travel above the speed limit. What if you’re distracted by a cell phone and your reaction time increases? What about senior citizens and the aging population with slower reaction times? What if it’s raining or icy? What if the road is downhill, as Henderson is? The required stopping distance will increase, making a longer yellow all that more essential. Of course, there is an alternative to increasing the yellow time. A 4.0 second yellow time could be sufficient at a speed limit of 40 MPH. Lowing the speed limit and leaving the yellow time alone could be even more safe.
Now I’m not a big fan of arbitrarily changing speed limits, so I would advocate the following steps:
1. Find the existing 85th percentile speed. If it is lower than 50 MPH, lower the speed limit to match it immediately.
2. Make sure there is enough yellow time as discussed above.
3. If the speeds are 50 MPH or above, the character of Henderson Road must be changed so it feels more like a 35 MPH urban boulevard instead of a 50 MPH expressway. Plant trees in that ugly median from Knightsbridge to Reed Rd. Install sidewalks and bus shelters. Use 10 or 11 foot lane widths. Install bike lanes as called for in the Bicentennial Bikeways Master Plan. Make new buildings front the roadway.