Mike on Traffic

Are LED Lit Pedestrian Crossing Signs Effective?

Here is a before/after study ( Download Elm Creek Blvd Ped Crossing Study) we just completed studying the effectiveness of a new push button activated, LED lit pedestrian crossing sign (thanks to Marc Culver at the City of Maple Grove for letting me share this with you).  We collected data (from video) for 12 hours on two days before and two days after the sign installation (48 hours total of data).

The hope is this type of sign would cause vehicles to yield to pedestrians more frequently than with the standard crossing signs.  Unfortunately, we found negligible difference in vehicles yielding to the pedestrians with the new signs compared to the yielding at the old signs. 

BUT, that was largely due to only 7 pedestrians pushing the button in the after condition (and 5 of those could cross without any cars coming).  The punchline is that we don't know if these LED lit signs cause vehicles to yield more frequently to pedestrians (compared to typical pedestrian crossing signs) because pedestrians don't push the buttons to turn them on.

Shared Space Roads - A Primer

The "Shared Space" road is a throw back concept in which pedestrians, bicyclists and vehicles are equals in using a road space.  There are a few proposals for Shared Space roads being brought up in the U.S.  (Shared Space immediately makes me think of the 19th/20th turn of the century photos of New York City.  I don't think proponents of Shared Space want to invoke that image though.)

By removing curbs and traffic signs, we expect motorists to be more cautious because the environment isn't giving them the impression that they're superior.  At least that's what Hans Monderman found with his experiments in Europe.

As I have written many times before, I am a minimalist when it comes to signs and other traffic control devices.  Only install them where they're needed.  So I somewhat agree with the Shared Space (or living street as others have called it).

The key with Shared Space is to keep the number of vehicles on it low (as my mentor Shelly Johnson taught me - all traffic designs work great as long as there aren't any cars, but your design better be very good if you have heavy traffic).  Here's my checklist if I was brought a Shared Space road to review:

• Designed so vehicles would have a very difficult time going over 20 mph.
• Need fantastic gateways into the street segment letting motorists know they are entering a different kind of road.
• I don't think I'd want transit on it because designing for LRT or buses would open up the road and make it easier for cars to go over 20 mph.
• Heavy landscaping and sight lines designed for the 20 mph speed (or 15 mph).  No over-engineering.
• Better be an area that will have a lot of pedestrians.  Otherwise, don't bother.
• No curbs.
• No signs.

I'd be open to a Shared Space road in my neighborhood, but it definitely shouldn't be on an arterial street.  The concept should start on neighborhood roads or in commercials zones that are a destination.  Don't bring the concept of Shared Space to the U.S. on roads that are meant to move motorists regionally.  And vehicle speeds MUST be kept low on them so they don't become a safety problem.  The traffic engineer would have to throw out their expectation of limiting the amount of delay motorists experience.

HCM 2010 Volume 4 - Online Login/Password for Free (plus review of the Enhanced Planning Methods Webinar)

The fourth volume of the 2010 Highway Capacity Manual is a living document online at http://hcm2010.org.  If you don't want to spend $275 on the 2010 HCM, but still want to poke around the fourth volume, go to http://hcm2010.org/login and use my info -

• Email:  mspack@spackconsulting.com
• Password:  CountingCars.com

We've been shutdown by the man!  I solemnly pledge I won't broadcast the new login/password they're giving me.  If you'd like to discuss this policy of TRB's please email me at mspack@trafficdatainc.com.

On a side note, I sat in on the HCM 2010 Webinar yesterday titled Enhanced Planning Methods and Applicaiton of Generalized Service Volume Tables.  No major revelations to report back on.  Basically, this section of the Manual gives methods for doing quick calculations to figure out a roadway's general capacity. 

It would be great if each section/chapter in the Institute of Transportation Engineers would do these calculations for their region as a recommended guideline.  This would allow us to say a 2 lane road in Raleigh, NC has a rough capacity of xx,xxx cars per day instead of every traffic engineer doing their own calculations.  Of course traffic engineers could do more refined analyses if they think they're justified, but it would nice to have consistent levels as a starting point for each region of the country.

Centerline Rumble Strips - Annoyance or Real Safety Measure?

I just read through a research paper from the Washington State Department of Transportation (WSDOT) that looked at the safety effects of putting a rumble strip down the centerline of two lane highways.  WSDOT started aggressively installing these rumble strips down the middle of their two lane roads in 2004 and have enough/before after data to be able to draw statistically valid conclusions.

Minnesota uses rumble strips a lot on shoulders, but isn't as aggressive with putting them down the middle of the road.  The research found very significant crash reductions in crashes where motorists cross over the centerline into oncoming traffic.  These types of crashes were cut almost in half on roads that have the rumble strips.

Of course there is no magic solution when it comes to safety, but these rumble strips should probably be considered whenever undivided high speed roads are reconstructed.  The report recommended they are especially effective on two lane roads that have less than 8,000 cars per day, a 45 to 55 mph speed limit, and narrow shoulders.

The research found the rumble strips to be great at reducing crashes where people doze off and start swerving.  They're also effective in combating distracted driving.  In the age of texting and driving, rumble strips seem like an effective countermeasure.

HCM 2010 Update - Traffic Signal Webinar (+ Ped/Bike Webinar)

Traffic Signal Webinar

I listened in to the webinar ITE hosted last week regarding the traffic signal chapters in the new Highway Capacity Manual (aka HCM).  Here are the slides from the presentation - Download New Signalized Intersection Methodology.

I'm excited about the changes in the new HCM.  I think its a much improved tool for our use.  One downside is that the methodologies are more complex and iterative, meaning you'll need software to do the calculations.  But outside of college students, I don't know anyone who was doing these calcs by hand any more.

Here are some highlights from the webinar - 

• Procedure added for actuated phase duration so the Level of Service is based on utilizing the actuated phasing instead of us traffic engineers guessing what the average cycle length is.
• Improved delay and queue length calculations based on research.  Maybe we won't have to jump straight to micro-simulation for traffic impact studies.
• Peak Hour Factor - for whole intersection, no longer by approach or movement.
• Level of Service gradation - if volume/capacity is over 1.0 intersection is listed at F even if delay would indicate better Level of Service.
• Based on dual ring controller structure.
• HCM 2010 includes only stopped vehicles in queuing calculations where HCM 2000 included slowing vehicles.

Multi-Modal Webinar

I also attended the webinar on the Multi-Modal Urban Streets methodology a month ago, but didn't write about it at the time because it doesn't seem very applicable to me.  Here are the slides from that webinar if you're interested - Download HCM - Ped - Bike - Transit Methods.  My takeaway is that we won't be incorporating these methods in Traffic Impact Studies and that the calculations can be largely skewed by inputs that are subjective.  I can see the methodology being useful for those doing a corridor study.  I'm sure the analyses will become more refined and less subjective over time.

Buy a Traffic Calming Device at Costco

Thanks to Nick Erpelding (a friend of mine who's a traffic engineer at Westwood Professional Services) for sending me this photo of the "Traffic Calming Turtle."  Nick tells me they're on sale at Costco (I'm working on a study for Costco so I feel like I should pass on this promotion).  It's just in time for the spring speeding problem on your street.  I have a neighbor who puts one of these out in my alley.

I prefer to put out a tricycle, wagon or ball when my kids are out playing.  I think a bunch of toys by the side of the road or the alley does a better job of slowing down cars than any kind of "official" sign. 

Nick tells me he was bummed out when the city filled in the potholes in front of his house.  They were great for traffic calming.  He's gone ahead and planted some trees in his front yard to eventually make the road feel narrower.

HCM 2010 Update - Stop Sign & Roundabout Webinar

Here are the slides from yesterday's webinar (Download Unsignalized HCM 2010 Presentation).  Highlights from the discussion -

Roundabouts

• This whole chapter is new.  We can finally compute Level of Service for roundabouts!
• Capacities at roundabouts in the U.S. are currently much lower than capacities observed in other countries.
• Calculations are based on simple models.  Experience in the U.S. shows roundabout performance is largely impacted by the variability in driver behavior, not specific geometrics configurations.
• Not included in the Level of Service calculations - geometric configurations (other than number/type of lanes), oversaturated conditions, or interaction effects of upstream/downstream intersections.  Other models should be used if these items are of concern.
• Delay thresholds are the same as those for stop sign controlled intersections, which are lower than the thresholds for traffic signals.
• On multi-lane approaches - the volumes in the two lanes are not assumed to be the same.
• There are calibration tools, which can ideally be tweaked based on local driving behavior data (this is true of the entire HCM 2010).

All Way Stop Sign Control

• Added methodology to model three lanes of approach instead of just two.
• New queuing model that is similar to the side street stop sign control method.

Side Street Stop Sign Control

• Added methodology to model six lane major roads instead of just two and four lane roads.
• Added methodology for modeling u-turns (our traffic counters will have more to keep track of).
• More refined method for dealing with the impact from upstream/downstream intersections.
• Better modeling of impacts of short left turn lane storage and large radii for right turn movements.

 

Highway Capacity Manual 2010: Review of ITE Overview Webinar

I watched the Institute of Transportation Engineer's webinar yesterday that covered an overview of the new HCM 2010.  This is a huge change from the 2000 Highway Capacity Manual (explaining why the 2010 HCM is coming out in April 2011.....).  Here are the slides from the webinar (Download HCMoverview).

Here are some of the highlights from the webinar:

• HCM 2010 is supposed to ship this week.
• ITE will have ten webinars to go over individual components of HCM 2010 (more info here)
• The three hard copy volumes total 1200 pages
• New elements
  • Multi-modal approach (ways to analyze bikes, peds, transit in addition to vehicles)
  • Chapter describing when/how to use advanced traffic analysis tools such as micro-simulation
  • Refined Level of Service criteria based on current research
  • Primer for non-technical audiences
  • Analysis accounts for actuated controllers and left turn lane queueing at traffic signals
  • Tools for analyzing roundabouts (this is probably my favorite update - we finally have a simple apples to apples way of comparing stop signs/signals/roundabouts)
  • All way stop signs - include three approach lanes instead of just two
  • Side street stop signs - considers traffic from adjacent intersections
  • Quick estimation method for interchange ramp terminals
  • Volume 4 is an online site that contains discussion boards/errata/additions.  Tools to make this more of a living document.

I plan to attend about half of the upcoming HCM 2010 webinars (assuming NCITE continues to host them for a $10 fee).  I'll post a summary for each webinar I've attended.  I'll also post some thoughts on the HCM once I have a chance to go through my copy.  I'm also considering posting my login/password for Volume 4 so all of my loyal readers can log onto the website (without having to buy the $275 book).  Stay tuned...

Minnesota Standards Should Change from 12 Foot Lane Widths to 11 Foot Lane Widths

I attended a luncheon about "Great Streets" at the Sensible Land Use Coalition yesterday.  The conversation was about MnDOT, Hennepin County, and HR Green's (a consultant working with local cities) experience of bringing the Complete Streets concept to Minnesota.  The main idea is to make our transportation system work for all modes of transportation (transit/bicycles/pedestrians in addition to vehicles).

Julie Skallman from MnDOT explained the excruciatingly slow process MNDOT is undertaking to implement Complete Streets concepts.  To me, the no-brainer decision is to use 11 foot wide lanes instead of 12 foot wide lanes. However this is in conflict with the Minnesota design rules which state "wherever possible, lane widths of 12 feet, rather than 11 feet, should be used."  

Narrowing roads results in shorter crossing distances and reduced traffic speeds.  This improves the environment for pedestrians and bicyclists. 

The research also points to 11 foot lanes being as safe as 12 foot lanes (according to NCHRP Project 17-26).  A big reason is that motorists drive more cautiously in narrower lanes.  Narrower lanes would have reduced the numerous speeding complaints I received from residents during my tenure in Maple Grove.

A quick check of MnDOT's website shows there are 290,588 lane miles in Minnesota.  Assuming we trimmed one foot off each lane, that would equate to 35,222 acres (55 square miles) of less pavement (assuming all of the roads are paved).  To put that in perspective, the city of Minneapolis is 58.4 square miles including the lakes and rivers. 

Imagine the economic and environmental benefits of shifting the standard by one foot.  Why would this decision take 2+ years of study?  The rules should be re-written to make 10 foot lanes allowable in urban settings, 11 foot lanes the standard across the state, and 12 foot lanes allowed if justified through a variance process.

How to Forecast Hourly Volumes for Signal Warrant Analyses...

Tim Aziere, PE, PTOE from Baughman Company in Kansas emailed me this interesting question –

I am doing a signal warrant for a proposed mix-use development here in Wichita. The existing land use is a golf course and the proposed uses (10 of them) will generate over 43,000 veh/day. I have little doubt that a signal at the major entrance (two entrances proposed) will be warranted, but I am having trouble finding a credible way of distributing the daily traffic for the warrant analysis. Is there a program I am not aware of, or an industry standard I could use?

Signal Warrants Background

There's a technical process for analyzing traffic volumes at an intersection versus different criteria in the Manual on Uniform Traffic Control Devices to determine if a traffic signal is needed at an intersection (the criteria are called warrants to confuse the layman). "Engineering judgment" is sprinkled in to let us professional engineers interpret the tea leaves. 

Most of the criteria are based on the busiest eight hours of traffic volumes.  Traffic impact studies typically just forecast one or two peak hours.  The big question is how to estimate the eight busiest hours of traffic based on the peak hour forecasts.

My Response on How to Forecast Hourly Volumes for Signal Warrant Analyses

I've been in your situation half a dozen times.  I don’t know of a perfect, industry standard method.  The two routes I’ve taken:

1. Get a 24 hour count on each of the roads your studying with the data broken down hourly (or a nearby road if things aren’t built yet).  Assume the same hour by hour distribution will apply before and after the development.  So if your peak hour is from 5-6 pm; your 4-5 pm hour is probably 95% of the peak hour, 3-4 pm hour is probably 85% of the peak hour, 2-3 am is probably 5% of the peak hour, etc.  I assume you have p.m. peak hour turning movement forecasts that you can add up to give you the total flows into the intersection.  Apply the hourly ratios to distribute based off of the p.m. peak hour having a factor of 1.0.     
2. Go to NCHRP Report 365 – Travel Estimation Techniques for Urban Planning.  It has a series of tables in Chapter 8 that give hourly distribution factors for different types of land uses sliced by the population size of the overall metropolitan area.  You can use those factors to factor your peak hour forecasts into hour by hour forecasts.

Neither method accounts for an area that has highly directional patterns (residents go to work in the a.m. and come back in the p.m.) and I wouldn’t use either method for an intersection that was right on the bubble of meeting warrants.  But these are reasonable methods to back up your engineering judgment if you strongly believe a signal is needed.