Tools you can use.
This compliments the US 2010 Highway Capacity Manual.
From: Parks, Jamie
Sent: Friday, November 16, 2012 10:13 AM
To: members@lists.apbp.org
Subject: Pedestrian LOS for Unsignalized Crossings (plus Spreadsheet Tool)
Hi All,
Apologies in advance for a long, but hopefully helpful email.
Most of you are likely aware of the new multimodal LOS procedures in the 2010 Highway Capacity Manual that produce LOS A-F scores for pedestrians and bicycles along street segments and at signals. Fewer people (or so it seems to me) know that the HCM also has a new method for Pedestrian LOS at Unsignalized Crossings (found in Chapter 19: Two-Way Stop-Controlled Intersections). The method uses traffic volumes, crossing distance, and the likely yielding behavior resulting from any traffic control devices that may be present (e.g., rapid flash beacons) to estimate pedestrian delay which in turn determines the LOS grade. Default yield rates for common treatments are provided based on NCHRP 562 and other research, but can be supplemented/adjusted based on local experience.
The intent is to complement the NCHRP 562: Pedestrian Safety at Unsignalized Crossings and FHWA Safety Effects of Marked versus Unmarked Crosswalks studies to (1) provide positive guidance on what treatments are likely to be most effective for a given location and (2) demonstrate the need for/impact of crossing investments using a readily understood metric (i.e., LOS). A quick example of how this works for a road diet and rapid flash beacon applied to a 4-lane undivided highway:
Before Conditions:
4-lanes, undivided
44 foot crossing distance
2,000 vehicles per hour
10% yield rate (based on standard marked crosswalk)
Results: Delay = 600s, LOS = F
Note: actual pedestrians would not wait 10 minutes to cross here. They would likely walk to the nearest signal, pick a small gap in traffic and run, or cross "frogger-style" where they do not wait for the entire roadway is clear to begin crossing. The point is that any of these results are extreme inconveniences to pedestrians, and potential safety hazards.
Conversion to 3-lane section with median island:
2-lanes, divided
11 foot crossing distance (x2 for each stage)
1,000 vehicles per hour (x2 for each stage)
10% yield rate
Results: Delay = 15s, LOS = C
Conversion to 3-lane section with Median Island (plus Rapid Flash Beacon):
2-lanes, divided
11 foot crossing distance (x2 for each stage)
1,000 vehicles per hour (x2 for each stage)
80% yield rate (based on rapid flash beacon research)
Results: Delay = 4s, LOS = A
The results show dramatic improvements for pedestrians from the road diet, which could be used to justify the expense or demonstrate the benefits of such a conversion (especially useful if the conversion were to degrade auto LOS). Compared to the urban streets Ped LOS, the methodology is easy to apply and generally provides intuitive results (for instance, road diets actually DEGRADE urban streets ped LOS in many cases). Of course I may be biased, since I helped develop the unsignalized methodology!
Anyway, the biggest downside to the unsignalized methodology is that is requires a lot of math (probability associated with yielding across multiple lanes, etc.), and it recently came to my attention that unfortunately none of the 2010 HCM software yet includes the methodology. To that end, I have created what I hope is a user-friendly spreadsheet/computational engine to implement the procedures. With this spreadsheet, getting results takes only a couple minutes (I spent 4 minutes putting together the example shown above). I've placed a copy of the spreadsheet on my Dropbox here: https://dl.dropbox.com/u/92064587/Ch19_PedLOS.xlsx. Please take a look, play around with it, and see what you think. I've left everything unprotected so that people can what's going on, check the formulas, and alter it for their purposes, but please use caution not to disrupt the calculations!
If you've read this far, thanks for bearing with me. Please feel free to let me know if you have any questions.
Best,
Jamie
Jamie Parks, AICP
Complete Streets Program Manager
City of Oakland | Public Works Agency | APWA Accredited Agency
250 Frank H Ogawa Plaza, Ste 4314 | Oakland, CA 94612
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