List serve thread summary: Truck apron at corner radius
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List serve thread summary:
Truck apron at corner radius
Contributors: Pierre‐Luc Auclair, Janet Barlow, Tom Bertulis, Jonathan Hawkins, Tony Hull, Steve
Jorgensen, Norma Moores, Shelley Oylear, Lois Thibault
Michael Ronkin posted this query to the list on March 4; some posts have been edited to shorten
and summarize the responses. To read the full text of the discussion as posted, sign in to the list
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This is an idea that’s been floating around for a good 10 years, and now I’m wondering if any
have been built successfully. To clarify the concept:
To keep a corner radius tight, but to still allow an occasional large truck to make a right turn, a
larger radius is traced in concrete (for trucks), but a tighter radius is extended (for people),
made of a different, rougher material, often cobblestone, to discourage passenger vehicle
drivers from driving over it and making a fast turn. The name derives from the truck apron of
the central island in a roundabout; they both serve more or less the same purpose. If you’ve
been involved in implementing one, or you know of one, please send graphics and photos, and
please answer some questions.
Continued 
List serve thread summary:
Truck apron at corner radius
1. Has the apron held up over time with trucks driving over it?
2. Do bicyclists ride over it when they make right turn?
3. Where are the detectable warnings placed?
Janet Barlow responded: You place the detectable warning surface where you want all
pedestrians (including those who are blind) to wait. I also assume you time any
pedestrian signal for the time needed to cross the entire road, not just crossing from the
extended truck apron area.
4. Is the crosswalk traced through the extended area to the larger curb return, or does it stop
at the tighter radius?
5. Have there been any complaints?
6. Was there much resistance from the project manager and/or designer in charge? Is so, how
did you overcome it?
7. Are most motorists actually deterred and follow the tighter radius, or do they cut the
corner anyway?
Truck apron at corner radius
Design Considerations
Corner radii:
• The radii would have to be individually calculated for each corner. An example for an urban intersection
might be 10 feet and 25 feet (3 m and 8 m). What’s particularly instructive is the huge disconnect between
urban and suburban design. We’ve held courses where there’s a mix of attendees, and the state DOT (or
county) will not accept anything under a 30‐foot radius (40 feet preferred), and the city wants no more
than 25 feet (15 feet preferred). (Michael Ronkin)
• Typically the passenger car radius can be 5 m, or smaller if bike lanes increase the effective radius of the
corner; the truck radius is often designed as a two‐centred compound curve and their radii will depend on
the design truck to be accommodated (city bus, tractor‐trailer, etc.) (Norma Moores)
• It's instructive, I think, to look at the radii of mid‐block alleys ‐‐ usually very tight. In my DC neighborhood,
they're 5‐10 feet, yet easily managed at low speed even by garbage and moving trucks because the
effective radius is provided in the street lane. In my other neighborhood, the effective radius is in the
intersection because the stop bars are held far back. (Lois Thibault)
• Guidelines in the UK allow curb return radii as small as 2.0 meters (6.6 feet) and I think eventually we’ll get
there too. (Tom Bertulis)
Detectable Warning: You place the detectable warning surface where you want all pedestrians (including
those who are blind) to wait. I also assume you time any pedestrian signal for the time needed to cross the
entire road, not just crossing from the extended truck apron area. (Janet Barlow)
Truck apron at corner radius
Design Considerations
Corner radii:
• The radii would have to be individually calculated for each corner. An example for an urban intersection
might be 10 feet and 25 feet (3 m and 8 m). What’s particularly instructive is the huge disconnect between
urban and suburban design. We’ve held courses where there’s a mix of attendees, and the state DOT (or
county) will not accept anything under a 30‐foot radius (40 feet preferred), and the city wants no more
than 25 feet (15 feet preferred). (Michael Ronkin)
• Typically the passenger car radius can be 5 m, or smaller if bike lanes increase the effective radius of the
corner; the truck radius is often designed as a two‐centred compound curve and their radii will depend on
the design truck to be accommodated (city bus, tractor‐trailer, etc.) (Norma Moores)
• It's instructive, I think, to look at the radii of mid‐block alleys ‐‐ usually very tight. In my DC neighborhood,
they're 5‐10 feet, yet easily managed at low speed even by garbage and moving trucks because the
effective radius is provided in the street lane. In my other neighborhood, the effective radius is in the
intersection because the stop bars are held far back. (Lois Thibault)
• Guidelines in the UK allow curb return radii as small as 2.0 meters (6.6 feet) and I think eventually we’ll get
there too. (Tom Bertulis)
Detectable Warning: You place the detectable warning surface where you want all pedestrians (including
those who are blind) to wait. I also assume you time any pedestrian signal for the time needed to cross the
entire road, not just crossing from the extended truck apron area. (Janet Barlow)
Burlington, Ontario
These are associated with
“urban smart channels”
Photos courtesy of Norma Moores, IBI Group,
Toronto
Burlington, Ontario
I’ll try to answer the questions based on limited observations:
1. Has the apron held up over time with trucks driving over it? It’s about 2 to 3 years
old and looks in good condition
2. Do bicyclists ride over it when they make a right turn? No
3. Where are the Detectable Warnings placed? At the bottom of the curb ramp but
“outside” the apron.
4. Is the crosswalk traced through the extended area to the larger curb return, or
does it stop at the tighter radius? Curb ramp continues through the apron
5. Have there been any complaints? NA
6. Was there much resistance from the project manager and/or designer in charge?
Is so, how did you overcome it? Several locations have been retrofitted. Design
process was initiated by engineers responding to complaints from pedestrians
and motorists at one location and lead to implementation in other locations.
7. Are most motorists actually deterred and follow the tighter radius, or do they cut
the corner anyway? Deterred
Norma Moores, IBI Group, TorontoBend, Oregon
A textured truck apron and raised
crosswalk at the corner of 3rd St.
(Business 97) and Mt. Washington Drive
Photos courtesy of Steve Jorgensen, Planning
Manager, Bend Metro Park and Recreation DistrictPortland, Oregon
This is a high truck traffic route, at the east end of
the St Johns bridge leading to the Port of Portland.
Bicyclists can ride over [the aprons]; they feel like a
big speed bump or there is a gap at the curb that
you can use if it isn’t filled with debris. I see good
compliance from vehicles, and it has made it safer
to cross the street keeping vehicles from
encroaching into the crosswalk.
Photos courtesy of Shelley Oylear, Bicycle
and Pedestrian Coordinator, Washington
County, OR
http://www.flickr.com/photos/shelley-o/sets/Washington State 1. Has the apron held up over time with trucks driving over it? Yes, they hold up fine. Same as the center truck aprons on roundabouts. And they hold up much better than sidewalks that trucks drive over. 2. Do bicyclists ride over it when they make right turn? No, cyclists tend to go around them. 3. Where are the detectable warnings placed? “You place the detectable warning surface where you want all pedestrians to wait.” (Barlow) That means the location of the detectable warnings are in the same place if you do or don’t install a right‐turn truck‐apron. 4. Is the crosswalk traced through the extended area to the larger curb return, or does it stop at the tighter radius? Zebra markings stop at the tighter radius. There is also the option of placing the crosswalk before the right‐turn truck‐apron begins. 5. Have there been any complaints? No. 6. Was there much resistance from the project manager and/or designer in charge? Is so, how did you overcome it? It was the designer’s idea, and WSDOT came on board rather quickly. 7. Are most motorists actually deterred and follow the tighter radius, or do they cut the corner anyway? Motorists are indeed deterred and generally will follow the tighter radius. If they did want to hop up on the apron they would have to do it at a lower speed. Note that if the apron is too small, half an inch or an inch tall, then it is less useful. But a three‐inch apron is a good deterrent to encroachment. Tom Bertulis, Northeastern University, reporting on a conversation with Victor Salemann of David Evans and Associates who has designed several of these facilities. E‐mail TomBertulisWALC@gmail.com for photos of these facilities: SR 20/Patrick Street Roundabout, City of Sedro Woolley SR 202/145th Roundabout, City of Woodinville East Lake Sammamish Pkwy/SE 43rd Street, City of Issaquah West Valley Mall Boulevard, City of Yakima
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