Comments on: Drivers: It’s not your fault (sort of). http://columbus-ite.com/2008/07/17/drivers-its-not-your-fault-sort-of/ Thu, 11 Mar 2010 21:23:36 +0000 http://wordpress.com/ hourly 1 By: johnwirtz http://columbus-ite.com/2008/07/17/drivers-its-not-your-fault-sort-of/#comment-184 johnwirtz Thu, 24 Jul 2008 01:25:39 +0000 http://columbusite.wordpress.com/?p=150#comment-184 By curbs being set back, I assume you mean that the corner radii are too large. The curb on the SE corner appears to have a 65' radius. The standard in Chicago is 15', maybe 25' if a lack of on-street parking forces vehicles to turn from the curb lane. The problem is that this intersection appears to have been designed so a large semi truck (called a WB-50) can make the turn comfortably. Unless we're expecting a huge volume of semi's at the intersection, that is silly. Like you said, in increases the crossing distances and passenger vehicle speeds too much. The design vehicle should be a passenger car or single unit truck (SU), while still accommodating WB-50s by allowing them to make wide right turns or encroach briefly and occasionally into oncoming traffic lanes. If the design vehicle must be a WB-50, channelized right turn lanes should be considered. As for all the turn lanes, I suspect that the intersection was designed with an over-reliance on the concept of <a href="http://en.wikipedia.org/wiki/Level_of_service" rel="nofollow">Level of Service (LOS)</a>. LOS is valued A through F and relates to congestion, density of vehicles, and seconds of delay per vehicle. Many DOTs require something like LOS C (stable flow) or better, based on traffic volume predictions 20 years in the future that are probably too high anyway. The only way to accomplish this is to over-build the number of lanes and turn lanes. Minor congestion must be considered acceptable in an urban area, especially where there are an abundance of alternate routes. The urban street grid excels at dispersing traffic among multiple routes. One of my favorite traffic engineers here in Chicago once said, "I've stopped caring about Level of Service and just started designing the roads the way I want the city to look." This is a man who is a former commissioner of the department of transportation and sits on many committees that write the AASHTO national design standards. I agree with him. By curbs being set back, I assume you mean that the corner radii are too large. The curb on the SE corner appears to have a 65′ radius. The standard in Chicago is 15′, maybe 25′ if a lack of on-street parking forces vehicles to turn from the curb lane. The problem is that this intersection appears to have been designed so a large semi truck (called a WB-50) can make the turn comfortably. Unless we’re expecting a huge volume of semi’s at the intersection, that is silly. Like you said, in increases the crossing distances and passenger vehicle speeds too much. The design vehicle should be a passenger car or single unit truck (SU), while still accommodating WB-50s by allowing them to make wide right turns or encroach briefly and occasionally into oncoming traffic lanes. If the design vehicle must be a WB-50, channelized right turn lanes should be considered.

As for all the turn lanes, I suspect that the intersection was designed with an over-reliance on the concept of Level of Service (LOS). LOS is valued A through F and relates to congestion, density of vehicles, and seconds of delay per vehicle. Many DOTs require something like LOS C (stable flow) or better, based on traffic volume predictions 20 years in the future that are probably too high anyway. The only way to accomplish this is to over-build the number of lanes and turn lanes. Minor congestion must be considered acceptable in an urban area, especially where there are an abundance of alternate routes. The urban street grid excels at dispersing traffic among multiple routes. One of my favorite traffic engineers here in Chicago once said, “I’ve stopped caring about Level of Service and just started designing the roads the way I want the city to look.” This is a man who is a former commissioner of the department of transportation and sits on many committees that write the AASHTO national design standards. I agree with him.

]]> By: columbusite http://columbus-ite.com/2008/07/17/drivers-its-not-your-fault-sort-of/#comment-181 columbusite Tue, 22 Jul 2008 18:48:26 +0000 http://columbusite.wordpress.com/?p=150#comment-181 The median wouldn't be so bad if the curbs on the intersection weren't ridiculously set back so far, encouraging cars to speed as they approach that median along with doubling the amount of street that pedestrians have to cross. I think you're right about the abundance of turn lanes there which leads to a wider road which of course ends up with cars going faster. I wonder what the justification was for making the intersection so suburban. The median wouldn’t be so bad if the curbs on the intersection weren’t ridiculously set back so far, encouraging cars to speed as they approach that median along with doubling the amount of street that pedestrians have to cross. I think you’re right about the abundance of turn lanes there which leads to a wider road which of course ends up with cars going faster. I wonder what the justification was for making the intersection so suburban.

]]> By: johnwirtz http://columbus-ite.com/2008/07/17/drivers-its-not-your-fault-sort-of/#comment-179 johnwirtz Thu, 17 Jul 2008 18:01:48 +0000 http://columbusite.wordpress.com/?p=150#comment-179 It looks like they were trying to create a gateway affect by placing the median, followed by a choker (narrowing), at the entrance to Victorian Village. It looks like the street is plenty wide for bike and cars side-by-side until they get to the choker, which leaves approximately 22' of street width. Chokers are meant to improve pedestrian safety by providing a shorter street crossing distance, but in this case it forces cyclists to take the lane. That reinforces the need to think about all modes of transportation when designing streets (complete streets). On a bike route like Front/Park, I would have prefered that the street remain 28' wide. 14' is the recommended width for a shared car-bike lane. The median isn't so bad though, is it? Otherwise, I would say that maybe we don't need so many turn lanes. A shared right-through lane once in a while wouldn't be so bad. The corner radii at Park & Goodale also look really large for an urban area. It looks like they were trying to create a gateway affect by placing the median, followed by a choker (narrowing), at the entrance to Victorian Village. It looks like the street is plenty wide for bike and cars side-by-side until they get to the choker, which leaves approximately 22′ of street width. Chokers are meant to improve pedestrian safety by providing a shorter street crossing distance, but in this case it forces cyclists to take the lane. That reinforces the need to think about all modes of transportation when designing streets (complete streets). On a bike route like Front/Park, I would have prefered that the street remain 28′ wide. 14′ is the recommended width for a shared car-bike lane. The median isn’t so bad though, is it?

Otherwise, I would say that maybe we don’t need so many turn lanes. A shared right-through lane once in a while wouldn’t be so bad. The corner radii at Park & Goodale also look really large for an urban area.

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