Mike on Traffic

Trainspotting - Modelling Gravel Trucks Through a Train Crossing

We're working on an interesting project for a gravel pit expansion.  The gravel trucks will turn off of a state highway onto a local street to get to the gravel pit.  This is a tee intersection with a right turn lane and bypass lane already built on the highway.  The intersection has side street stop sign control and low traffic volumes.

The big wrinkle is there's an active rail line paralleling the state highway.  There's about 50 feet of storage between the tracks and the highway.  The state folks asked if the bypass lane and right turn lane are long enough to store the increased truck traffic or should they be extended.

Modelling the geometry of the intersection/train tracks with Vissim is pretty straightforward.  The big wrinkle is getting good existing data to use as the foundation for the modelling.  In comes our COUNTcam system.

We set up several cameras and recorded the crossing and intersection for 48 hours on a normal Tuesday/Wednesday.  Over the 48 hours, there were 68 trains that caused the gates to go down at the crossing.  Each crossing lasted about two minutes.  For each train crossing, we noted:

• Time gate went down
• Time gate went up
• Number of cars in bypass lane after train cleared
• Number of cars in right turn lane after train cleared

Then we picked out a couple of time frames that have the most vehicle stacking combined with our added gravel trucks and conducted turning movement counts for those intervals.

This data allowed us to calibrate to the most intense existing conditions and then layer our increased trucking onto that period.  Without our video system, collecting this existing data would have been very expensive and there's a chance we would have missed something in the field.  With our COUNTcams, we were able to watch the videos several times and get different angles so we could efficiently hone in on the intervals we should model.

How Long Should a Turn Lane Be?

Minnesota's Road Design Manual sets the default left turn lane at 300 feet long with a 15:1 taper into it (180 feet to taper a 12 foot lane).  If you look around Minnesota, the vast majority of turn lanes follow this default.  Unfortunately, those exact dimensions are wrong almost every single time.  They're either not enough or too much.

MnDOT funded a study to get at this issue and they put together a technical report last year - Design of Turn Lane Guidelines.  The steps to designing the proper turn lane length are:

1. Collect Data (design traffic volumes, speed, % heavy trucks, grades, etc)
2. Determine Facility Type (rural, urban, suburban, traffic control)
3. Calculate Turn Lane Demand (store 2 minutes of traffic at a stop sign or traffic stacked in one red cycle at a signal)
4. Calculate Turn Lane Design (Design the storage and taper based on above)
5. Document (cover your  tail - file away your calcs, conclusions, and recommendation)

The document does a good job of laying out the design process and even provides several example cases to show the design process in action.  A lot of reference tables are provided to help you quickly make all of the potential adjustments away from the default 300 feet/ 180 feet.  I hope designers move away from the default and think through the appropriate turn lane geometry for their specific situation.

2012 National Traffic Signal Report Card - We're Improving

The National Transportation Operations Coalition released the 2012 report card this week.  As a country, the U.S. came in at a D- in 2005, D in 2007, and D+ in 2012.  We're improving even in a down economy with budgets being cut!

This is a big deal for the nation.  Approximately 295,000,000 hours of delay are attributed to traffic signals annually according to FHWA's Congestion Reduction Toolbox.  Improving signal timing has about the best benefit to cost ratio of all of the things traffic engineers can work on.

Traffic monitoring and data collection is the poorest rated line item in the report card.  Definitely an item near and dear to me.....

 

How to Cut Congestion in Half......

match all of the people driving by themselves during rush hour so every car would have two to three commuters in it, leaving half the cars at home.

It is a sad fact that the majority of cars on the roads during rush hour have just one person in them.  Ridesharing to date has a very lackluster track record.  Americans are just too tied to their little slice of the American dream - which in most parts of the country includes driving to work by yourself in your own car.

Minnesota is investing heavily in managed lanes - toll lanes where carpoolers can drive for free.  The first was I394, then I35W, and several more are being planned.  If all of the interstate highways running through the Minneapolis/St. Paul area have managed lanes, there would be a massive incentive for commuters to figure out carpooling.  It wouldn't be a silver bullet, but reducing peak traffic flows by a few percent is the difference between rush hour moving at 45 mph versus stop and go.

The Ridesharing Institute and the Transportation Research Board are holding a joint symposium on the topic in Oakland, CA on May 24th.  A portion of the symposium will be a free two hour webinar.  Details here.

p.s.  Another crazy option - instead of the two seat small car that is as wide as a normal car (and takes up the same long following distance as a normal car), put the seats in line like a fighter jet cockpit.  These 3 feet wide cars could get away with a lane that is roughly half as wide as the standard lane.  We could squeeze in a lot of these lanes and shift folks to a commuter car.  I know, good luck.....

 

Minnesota Manual on Uniform Traffic Control Devices Update

The Feds updated the national MUTCD in 2009.  States have the choice of just adopting the Federal manual or they can adopt their own version (which has to be largely the same as the feds).  If a state chooses to publish their own manual, they have two years to finalize there version after the feds come out with a new edition (hence Minnesota updated their version in December 2011).  

Quick Primer 

The MUTCD is the book of standards that regulates the use of traffic control devices (signs, pavement markings, signals, etc) so drivers across the U.S. can drive anywhere and understand the traffic control devices - i.e. we want all stop signs to look the same because it makes driving easier and safer.  Here's the Federal version and here's the Minnesota version.

Highlights of 2011 MN MUTCD Changes

I attended the NCITE luncheon today where Janelle Anderson (MnDOT Tort Claims & Traffic Standards Engineer) gave an overview of the big changes in the 2011 Minneosta manual (a lot of which were drivern by the changes to the 2009 Fed manual).  She didn't have time to go over the 400+ changes, but she did give a great overvview.  Here are some of my big takeaways - 

• The manual applies to ALL roads that may be travelled by the public.  So private property is now goverened by the manual.  No more blue stop signs within private street developments.  Huge gray area on this - What's a parking aisle and what is a public street?  Janelle didn't have good guidance on this.
• Compliance date for getting the retro-reflectivity of signs and lane marking up to standards has been delayed.  New devices need to be up to standards and each agency needs to have a plan in place by now for managing their inventory, BUT the federal mandate to change over signs has been softened.  Getting signs up to date can happen through attrition, so it's not the huge budget hit many were fearing (including me).
• Street name signs - can't be all caps anymore.  All new signs need to have street names capitolized (first letter upper, rest lower case).
• Lettering is bigger now to accommodate 20/40 vision.  This is a change based on our aging population.
• All school related signs must be fluorescent yellow green.
• Added yield signs to discussion of when to install stop signs.  Trying to encourage more yield signs.  I'm a big fan of eliminating stop signs in neighborhoods - this is great.
• Any of the different signs can now be made fluorescent under the new manual.  Not a fan of this.  We're in an arms race to get the motorists attention.  Eventually every road could feel like Times Square.
• Lane drops - need to use dots instead of short dashes on the pavement transition.
• New chapter on rumple and stripe strips.
• Flashing don't walk at signals - based on a walking speed of 3.5 feet/second instead of 4.0 feet/second.
• Anyone working within the public right-of-way is required to wear high visibility clothing.

 

Free Exhibitor Guest Passes to NATMEC: Improving Traffic Data Collection, Analysis, and Use Conference

Once again proving how much the industry likes acronyms - The TRB's biennial NATMEC (Transportation Research Board's every other year North American Travel Monitoring Exposition and Conference) will be held in Dallas June 4th-7th.  

CountingCars.com will have a booth there and we have 25 guest passes to give away.  Email your business card to mspack@countingcars.com and I'll get you a free pass to the exhibits.  Of course, first come first serve on these hot tickets.

 

New Traffic Safety Analysis Manual

There are a lot of really good NCHRP reports on traffic safety, but they are pretty specific in addressing a specific aspect of safety.  The Institute for Transportation at Iowa State University has put together a great summary on traffic safety - the Traffic Safety Analysis Manual.

The target audience for the Manual are public agency engineers, not specifically traffic engineers.  The intent is to provide a basic primer with a lot of useful checklists and a step by step process for improving safety.  The authors hope city and county staff engineers will be able to use the Manual to improve safety in their jurisdiction.

The first few chapters are pretty Iowa specific, but the later chapters provide general information any engineer can use.  My favorite sections are the checklists of Issues/Countermeasures on pages 40-44 and 80-84.  This is a very handy reference.  Check it out.

 

Student Apartments - Traffic Generation

There's been a housing boom around the University of Minnesota for about three years.  Very nice, new apartment buildings are being built with underground parking garages.  The new trend seems to be that each student wants their own bedroom and most of these buildings are providing a range of unit sizes - a mix of studio to 4 bedrooms.

We've provided traffic studies/travel demand management plans on several of these proposed buildings.  One thing we wrestle with is what trip generation should we use?  We've used trip generation numbers from ITE's Trip Generation for the generic apartment land use, but that seems high.  Enough of these buildings are finally operating now that we decided to do a little trip generation study.

We were able to track down six buildings where we could easily video their parking lot driveways AND get building statistics.  We've determined a.m. peak hour, p.m. peak hour, and daily trip generation rates Vs. number of dwelling units, number of parking stalls provided, and number of bedrooms provided.  Read our full study here  Download Student Apartment Trip Generation Study.

Below are the quick results compared to the average rates of a generic apartment building in ITE's Trip Generation, 8th Edition.  It's clear student housing generates low levels of traffic and a full traffic impact study will only be justified for very large complexes (roughly more than 400 dwelling units).  We were not able to capture bicycle data, but in our interviews of property managers it seems bicycle parking is a much bigger transportation issue than vehicle parking/traffic impacts.  Something designers should keep in mind.

Average Trip Generation Rates for Student Housing and Apartment per Number of Dwelling Units

	Student Housing Apartments	Apartment from Trip Generation, 8th Edition
Weekday	2.82	6.65
Weekday A.M. Peak Hour(between 7-9 a.m.)	0.13	0.51
Weekday P.M. Peak Hour (between 4-6 p.m.)	0.24	0.62

 

 

When to Install Protected Left Turn Phasing at a Traffic Signal

Dale Robinson emailed me wondering why some traffic signals with little traffic have protected left turn phasing (solid red arrow) while other signals have protected/permitted or even permitted left turn phasing (just a green circle).  He thinks this is a waste of time and increases vehicle emissions.  He's right!

Standards have evolved over time and often this decision comes down to engineering judgment.  Some traffic engineers don't trust drivers and want all left turn lanes at signals to have protected left turn phasing.  I disagree with that approach and fall in line with NCHRP Report 457, which says on page 42 - "the number of phases should be kept to a minimum because each additional phase in the signal cycle reduces the time available to the other phases."

So traffic engineers should always start with trying to get away with permitted phasing (no arrows).  If that won't work I'm a big fan of the Flashing Yellow Arrow protected/permitted left turn phasing.  This gives motorists a permitted signal most of the time so they can use their judgment, but if traffic is so heavy they can't turn it will eventually give them a green arrow.

There are a few conditions when protected (red/yellow/green arrows) should be used.  NCHRP Report 457 has a good decision tree in Figure 3.5.  Basically, go with protected left turn phasing only if you have one of these conditions:

• The movement has exceeded the critical number of crashes with the protected/permitted left turn phasing, so protected phasing is required to solve a documented safety issue.
• There isn't enough sight distance provided - meaning the motorists can't see oncoming traffic for a long enough period to judge if they'll have enough time to make the turn.
• There are two or more left turn lanes on the approach or the opposing approach.
• The left turn opposes more than three through lanes.

These situations are pretty rare except at big suburban intersections.  Most left turn lanes at signals should have permitted phasing or flashing yellow arrow protected/permitted phasing.

 

Good News for Traffic Engineers - Development on the Upswing?

The majority of traffic engineering/transportation planning is driven by new land development.  Of course, there’s the design of the access points into a development and the roads within the development.  But there’s also broader work that needs to be done to address increasing traffic levels.  But with traffic levels plateauing the last five years, local government revenues going down, and less development projects to work on – the public sector has also been significantly impacted by the economic downturn.

It’s no wonder then that a common discussion topic among folks in the industry is, “When is real estate development going to turn around?”  An article in today’s Star Tribune took a stab at answering this:

The Urban Land Institute asked 38 leading real estate economists and analysts from across the country when to expect better times for the commercial and residential construction industries. The consensus? Sunnier times are indeed ahead, but change will come slowly. Here's what to expect over the next three years:

• Commercial property transaction volume will increase almost 50 percent.
• Commercial mortgage-backed securities (CMBS) are expected to more than double.
• Real estate investment trusts (REITs) should provide returns ranging from 8.5 to 11 percent annually.
• Office, retail and industrial vacancy rates are expected to drop 1.2 and 3.7 percentage points; apartment vacancies will be stable and hotel occupancy rates will rise.
• Rents (for all property types) will increase from a range of 0.8 percent for retail to 5 percent for apartments.
• Housing starts will nearly double by 2014, and home prices will begin to rise in 2013, gaining 3.5 percent during 2014.

This lines up with what I'm currently seeing.  The phone's ringing more and developers appear to be cautiously optimistic about the next few years.

p.s.  The Star Tribune had another interesting article today regarding cities being able to assess traffic impact fees to developers:

A Ramsey County district judge has ruled that a Roseville ordinance allowing the city to impose an impact fee on developers exceeds the city's authority.  Judge John Guthmann declared Ordinance 1417 "invalid and unenforceable" in his 20-page ruling released Wednesday.