Tuesday, September 17, 2019

A Planner's Overview of Florida's Travel Demand Models

I've been applying travel demand models here in Florida for the last 22 years and been participating in the Model Task Force for at least a decade.  Florida is unique in that travel demand models are loosely managed at a statewide level.  We all use the same software (basically).  We have consistent naming conventions for filenames, processes, and variables.  We meet once or twice a year to discuss research that can go into improving the models.  We have a website that lists all of the different models that are available in each of the regions statewide.  Travel demand models are both an art and science, and you can tell who wrote or worked on each one from the internal code and overall structure--like telling a Monet from a Rembrandt.  Most of the models in the state are typical 4-step models with varying degrees of complexity in terms of transit choice and assignment routines.  Florida is really skilled at special generators--land uses that don't quite fit into the typical commuting pattern--because we have lots of them.  Some of the early data collection in the Orlando area used aerial photography to estimate vehicle counts at the theme parks.  I'm not sure we could even do that kind of data collection today both because the parks are so much larger and because of security and privacy issues.  At least 4 of the models in Florida are activity based models and they are painful to use.  I set one going for Tampa Bay (3029 zones) at 8 am this morning and it's not finished yet (at 6 pm)--and it's on a huge, fast computer.  In comparison, the CFRPM model (which is a 4-step model with about 5,000 zones) takes about 5 hours.  Going forward, we are working toward cloud computing for these projects, but security issues have slowed this considerably.  Model programmers are worth their weight in gold and the software isn't far behind in cost.  Cube cost me about $12,000 for the software about 4 years ago and they charge about 15% a year in maintenance.  Most of what I use it for is to generate trip distribution for projects that are in development review.  Nearly every jurisdiction requires a traffic study for new projects that mirrors the 4-step process (trip generation, distribution, (occasionally mode-split), and assignment) with operational analysis evaluated both for existing and projected conditions.      
Here are a few notes on applying travel demand models in real life planning:
1. Models are calibrated to roadway volumes based on the data inputs that are available.  That calibration is across the entire region, not based on any one roadway.  They are only supposed to be accurate enough to distinguish whether an additional lane is needed in the system.   Individual roadways may be off by 50% or more.  The bigger the roadway, the more likely it is to be accurate, but they can still be off by quite a bit.  Sometimes if the projection is off, we just look at the growth between the base year and the future year and apply that growth rate to existing counts to come up with the future base volume.  When we use that method, we also check that growth rate against the historic volumes on the roadway, with the caveat that we had national dip in traffic volumes between 2008 and about 2013 that affected every roadway, basically around the entire world.  
2. The farther out in time you look, the less trustworthy is the projection.  We generally create projections 15 to 20 years into the future, but take that with a grain of salt.  You can start thinking about a new corridor or roadway in that time frame, but you don't have enough information to take it to anything other than corridor location studies.  Five year projections are likely to be realistic across an entire corridor--it's probably ok to use those numbers for design traffic if you're careful.  If you're trying to project intersection counts or plan turn lane improvements, looking any farther than 2-4 years in advance is asking too much.  No one knows that much unless the area is very close to built-out.  I've done roadway projections 10 to 20 years in the future that I would trust, but only when I know everything that is going on around that location and I know that there is little that anyone can do outside of what is already built (and I whined the whole time doing it because it's just not a good thing to get people comfortable with). 
3. At some point it is important to manage expectations.  We may be able to do miracles with some help, but we don't do magic. Some things I can recalculate and make say what I want it to say.  Some things I can't.  If the volume projection is double or triple what the capacity is, then there's nothing short of new roadway that will make up the difference.  If it's within a few percentage points, people will adjust and there's usually tools to help make it work.  I have actually had a reviewer question a roadway projection because it was only 6 PM peak hour trips below the capacity.  He asked if I had made it do that on purpose and whether the number was realistic or the roadway needed improvement.  My response was, "Cool!  I didn't know it was that close."  I really didn't know it was that close--I had a check in the spreadsheet to see if it was over, but not how close it was.  The attorney for the client responded that if it were 6 trips over, they would make us pay for it, so forget charging us for it.  Such is the nature of development negotiations.
4.  Land use modelers and travel demand modelers are rarely the same group of people or even the same expertise.  Land use modelers are usually economic modelers that digest and process census trends.  Travel demand modelers are usually traffic geeks.  Yes, land use and transportation feed back on each other.  No, the interaction is too complex (to date) for those interactions to be understood, much less incorporated into the 4-step model.  Adding roadways to an area that is declining is like adding outflow pipes to an empty reservoir--the new pipe won't make any new water.  Adding a new pipe to an overflowing reservoir will make a huge difference both in the outflow and the reservoir (economic capacity).  Models can give you a good idea of what will happen in terms of traffic relocation, but it won't tell you how that will impact economic development unless things are growing so fast that congestion is getting in the way of growth.
5. Traffic forecasters are not psychic.  If there is a large redevelopment project that the local agency knows is in the works (has plans for and has approved) then it gets incorporated into the model.  Otherwise, redevelopment is rarely considered until the area is completely built out.  It's easier to build on empty land than rebuild on developed land. 
6. Growth in zones that are nearly built out may not actually occur because there's usually a reason it hasn't happened already--it is administratively contaminated and the local agency just hasn't realized it yet.  For instance, what happens when the required setbacks for a parcel are 30 feet from the property line and the property is only 70 feet wide?  It's really hard to build a 10 foot wide building and most developers won't even try an appeal.  This happens a lot in historic districts because any redevelopment or reconstruction means the property must be brought up to code, which may not be possible.  Unless the local agency identifies what is keeping orphan parcels from developing, it probably won't happen.
 7. Walking is a mode in the model but it doesn't count.  Same goes for biking.  Transit does get counted, but it's usually such a small percentage it doesn't even matter.  The rule of thumb we use in Florida is about 1.5% of all trips are transit trips, even in the areas with the best transit.  There's even a new Federal Transit Authority (FTA) process that reduces the complexity of the transit modeling because it's such a small impact.  Transit sections of the model are usually created to comply with FTA funding guidelines and analysis.  FTA models are even more complex than typical MPO models because they're asking for billions of dollars.  These models cost tens of millions instead of just millions.
8. Pass-by and diverted trips are not in the 4-step models in any large quantity, if at all.  Remember, the goal of most travel demand models is to predict roadway volumes.  Pass-by traffic doesn't impact roadway volumes.  
9.  Many of the simplifications that happen in the trip generation step are at least partially fixed in activity based models.  Activity based models also handle time of day better because it actually tracks travel by hour of day (or 15 minute period depending on the  model).  That's also why they take so long to run.  If you're running a model for a new project, it's not that hard to come up with the data to put in a new zone for that project in a 4-step model.  When it's an activity based model, things get strange.  Is your new subdivision going to have young families with small children?  Older families without children? Retirees?  You can model all of that in an activity based model, but making guesses for the percentages of people with different numbers of vehicles gets pretty  complicated. 
10.  Trip lengths depend on two things in the model:  average trip lengths for everyone in the model and the distance between origins and destinations.  It calibrates the outputs iteratively to get those two factors balanced.   As areas become more dense and congested, trip lengths (in time) will go down because things are closer together and go up because congestion increases the time to get places.  We hope those two effects balance out in the future.  Disruptive travel modes like TNC's and scooters are going to play havoc with our models in the future.  Our entire mode choice systems are going to have be completely revisited in the next 5 years based on the adoption of TNC's, bike-share, and scooter-share.  We haven't really even started to try to figure this out yet and it's a huge elephant sitting on the coffee table in the middle of the room. 
11.  There are calibration factors that can be used in the model to account for blighted areas, bad parts of town, rivers, bridges, or other cognitive/psychological factors that impact transportation, but modelers hate to use them because they don't trust them now or in the future.  River adjustments we trust, some days (but we don't like trusting them.)
12.  In Florida, the terminal time can be set as a factor for the zone or the area depending on the model.  Most models include the possibility to include long term and short term parking costs in the zone structure.  When you look through the socio-economic (SE) data, there are usually less that 5% of the zones that have a coded parking cost.  
13.  Intersection delay is only partially ignored.  The facility type designation often includes the number of signalized intersections per mile with a typical amount of delay per intersection, although it is not usually stated explicitly. 
14.  Model volumes can go way over capacity for individual segments.  The delay gets really bad, but it happens.  Most 4-step models have been daily models which means that an over-capacity segment just has more volume happening off-peak than normal (this is called peak-spreading).  Time of day models do this too, but not as much.  I assume (but don't know for sure) that activity based models can't be that flexible on their capacity designations.
15. Activity based models use a synthetic population.  They know the statistical characteristics of a zone and they create a set of households that conform to those statistics and then run them through activities.  It's not the real households, but it's close.  If I had a zone that was all kids and seniors, I'd worry, but that doesn't happen that often.
The Beimborn (1995) article has several suggestions that I thought were interesting:
1. Improved Bike/Ped Representation: California models currently have a much better representation of bicycle and pedestrian travel because they are required to.  Most of their models aggregate into zones, but include the parcel level data in the model along with all of the local streets.  That means they can actually assign the synthetic population to individual parcels and feed them out to the  zone centroid before they assign them to the roadway network if they're in a car.  Bike and ped trips generally stay within the zone itself, though in real life they can and do travel between zones.  This level of detail also helps better represent parcel access.  
2. They could use more trip purposes.  Maybe.  I have seen school trip purposes as a separate trip purpose in the Atlanta model and that would help some, particularly if it were coupled with the actual school district boundaries.  The CFRPM model actually changes the area type of the roadway (which changes the operating characteristics) based on the density/intensity of the SE data adjacent to that segment.  It's not the same, but it may have the same result as looking at different market segments.  Activity based models do market segmentation like the author describes automatically, but keep within the same 4 primary trip types.  
3. They could add land use feedback in the future.  (This is a "here, hold my beer" goal).  I'm not sure how well this can be done, if at all.  Not only is it a complicated technical issue, but also a subtle political issue.  Are modelers going to be comfortable projecting blight in an area (a decrease in future SE data) because a new facility has attracted that activity away from an existing developed area?  We know it happens.  No one wants to be the bearer of bad news.
4. Add intersection delays.  Can be done.   There are model platforms that do that now, particularly for small areas within larger regional models that are used for corridor studies.  Thankfully, we don't often do that here in Florida.  It's an issue of the accuracy you're trying to achieve with the overall model.  Remember, the model is only accurate across the whole model to +/- 1 lane.  That's a pretty wide margin of error.  Adding in intersection delays (that are already partially accounted for) would add another layer of complexity (read: computational time and expense) that would not add to the overall accuracy of the whole.  The technical term for this is "polishing the turd."  You're trying to take garbage and make it look like something better than it is.  
 I hope that helps.  It's a 50,000 foot view with a zoom lens.  If any of the modelers out there want to take issue with what I've said, I'm open to critique and will revise with the utmost of humility.  
Currans, K. (2017). Issues in trip generation methods for transportation impact estimation of land use development: a review and discussion of the state-of-the-art approaches. Journal of Planning Literature 32(4), 335-345.
Biemborn, Edward.  (1995).  A Transportation Modeling Primer. Milwaukee, WI: Center for Urban Transportation Studies.   Retrieved from http://www4.uwm.edu/cuts/primer.htm
Pihl, E. & Rousseau, G.  Introduction to Travel Demand Forecasting. Travel Model Improvement Portal (TMIP). Retrieved from https://tmip.org/content/introduction-travel-demand-forecasting

Tuesday, September 3, 2019

US Scooter Fatalities

I've been watching the scooter trend with great fascination since January, and have been remarkably surprised at the comparatively low fatality and injury rates.  Now that ride volume is getting much higher, we are beginning to see an uptick in fatalities, which shouldn't be a surprise.  The latest national numbers are pitifully old--2018 totals showed 35.8 million rides (NACTO 2019).  Since we are still in the exponential growth phase of this trend, I wouldn't be surprised to see that number double or treble by the end of this year.

As of August 22, 2019, there have been 16 scooter fatalities in the US.  To figure this out, I scoured the web for newspaper articles, summaries, and blogs.  The article links can be found at the end.  First let's start with the Memorial.  Here are the names, ages, and cities for the 16 fatalities I found in the order they occurred:


The average age was 30 with the majority in their 20's and a median age of 26.  The vast majority (13) were male. That's not surprising since early reports indicate that scooter use is skewed toward men in their 20's and 30's (Dill, 2019).  This is the same demographic cohort that grew up with Razor scooters as kids in the 1990's.  



Most of the fatalities were on the weekend (9) or at night (11), which gives credence to Atlanta's after hours ban.  All of the weekend fatalities were at 10 pm or later.  Surprisingly, alcohol was only indicated as a factor in 3 of the 16 incidents--which means they probably didn't ask in most of the cases.  Only one fatality occurred during peak travel hours.  Where a cause of death was indicated, head trauma was most often listed, although torso trauma was also mentioned.

It took 9 months before the first fatality occurred, but as usage increases, the time between fatalities is dropping rapidly with an average of one fatality every 14 days.  Scooters may be seen as a west coast phenomenon, but only 4 of the 16 fatalities occurred in California.   The city with the most fatalities is Atlanta, which has had 4 since May.  This is followed by Washington D.C. and San Diego with 2 each.  

Nearly all of the accidents occurred in the roadway (12) with 4 occurring at intersections.  Thirteen of the fatalities involved cars (10) or larger vehicles like buses or semi's (3).  Three of the incidents involved issues with being able to see a smaller vehicle with larger vehicles involved or in the area. One fatality involved a man on a scooter hitting a tree. The scooter rider was the most likely at fault in 12 of the fatalities.


The geometric information is interesting.  The vast majority of the fatalities occurred on or around roadways that were 4 lanes or more (12 of the 16), although it's clear that people can and will kill themselves in the most sheltered of locations.  Intuitively, I would expect most of the fatalities in the intersections, where the conflicts are most dense, but areas away from the intersection were more common.  Sidewalk riding was only allowed in 6 of the 16 fatalities, and this was clearly a factor in many of the incidents.  Onstreet parking was in the area of the incident 3 times but only appears to have had an impact twice.



So what do we need to do to keep people from getting killed? 

Looks like despite the frustration people have with sidewalk riding, there may be a good reason to allow them there, at least until the infrastructure catches up.  If the CDC study is any indication, the learning curve is a complication that probably doesn't belong in the roadway.  In Austin, the CDC found that 1/3 of the ER visits over a 3 month period were on the person's first ride and 63% were in the first 10 rides.  Imagine learning to ride a bicycle in the roadway alongside other cars--not good. The cars in the environment are also learning to recognize scooters in the ROW, which will also take time.  The good news is that people will learn and the accident rates are likely to drop.  The bad news is that people can kill themselves at 15 mph pretty easily even without another car around.  I would suggest helmet use, like everyone else, but many who fall from a scooter land on their chin, not the top of their head where the helmet is.  The European airbag collar might help, but helmets may not be of much use when a person gets hit in the body and dies from internal injuries.  By the way, I can't wait until we can get these in the US.

Clearly, scooter riding after 10 pm also seems to add substantial risks, and not just because of the weekend drinking crowd.  There seems to be an issue with low volumes and high speeds in urban areas on wide roadways.  Drivers are less likely to anticipate seeing anyone, much less a scooter.

From a design standpoint, intersection radii need serious consideration.  Many times, urban designers will specify 25 ft radii for curves to slow traffic, but bus traffic requires a 43 foot radius.  Running over a corner curb may be fine when pedestrians are there, but scooters and bikes can't move out of the way as quickly or easily.  Same goes for construction barriers.  Maintenance of traffic in light of scooters may need revisions.  

In the meantime, the numbers are still pretty low, all things considered.  They are likely to climb as scooters appear in more locations.  I'm going to try to keep up with the fatalities as they come in, so keep posted...

As soon as I can figure out how to post the locations on Google Earth, I'll update this with the link...


Dill, J.  (2019). Portland State University. https://www.slideshare.net/otrec/escooter-users

Wednesday, November 22, 2017

Another cool intersection painting project!




Tampa's first painted street mural — at the corner of N River Boulevard and W Louisiana Avenue — was finished on Saturday afternoon by neighborhood kids and parents and supervised by the artist who created the image, Catherine Thomas of St. Petersburg, pictured at left. Photos by SCOTT PURKS   |   Special to the Times
Seminole Heights Painted Intersection, Tampa Bay Times

I love these!  This is traffic calming at its best!

Painted Intersections are the incredible!  The draw your attention to the street and out of your head.  They say something about the area that created them.  The show that people care and this is a part of their home. They add value to the homes around them.  They're a great landmark for giving directions.  

They don't slow down emergency vehicles.  They don't rack your suspension. They don't make you speed up between them.  They probably encourage you to slow down in the entire neighborhood.  

All wins, no losses, low cost.  Kudos to Seminole Heights!

You can read more about this project in the Tampa Bay Times

Tuesday, October 2, 2012

Mixed messages

So what is it, Stop or Yield?
This would be comical if it weren't a photograph.  This picture goes to the core of why urban design is so critical and yet so ridiculed when poorly practiced.  The interface between people and vehicles is difficult to legislate.  Engineers like to have everything settled in firm rules that will forever be followed.  In our minds, indecision leads to insecurity, so every contingency must be considered and legislated out of existence. 

People are far more flexible than that.  Uncertainty and attention are friends of the pedestrian and it turns out, they are also the friends of community building.  Isabelle de Pommereau wrote in the Christian Science Monitor about Bohmte, a German village that has become another example in the evolving “Shared Space” movement.  Bohmte removed all of the signage and signalization in its town square.  So what happened to the 13,000 vehicles per day that used that square?  They're still there, but they behave quite differently and the people who walk and drive there see their lives differently.  One of the residents had this to say:

“Two months into the experiment, ‘Instead of thinking, ‘It’s going to be red, I need to give gas, people have to slow down, to look to the right and the left, to be considerate,’ says Ms. Rubcic…  ‘The whole village has become more human. We look at each other, we greet each other,’ she says.”

That's a big deal.  I could go for that. 

Notice that this is a downtown--a very urban environment where people and cars should share the space.  There's no confusion about whether people should be trying to get somewhere because they're already there.  That's what the planners and architects are talking about when they talk about "placemaking."  These are the places you're trying to get to, not the road on the way there.  You can clearly see that the minute you enter the space.  No mixed messages here. 

It's far too easy to confuse the destination with the path.  My friend, Chuck Mahron is talking constantly about the danger of Stroads--vehicle pathways that look like through paths but directly serve destinations.  So which is it--a destination or a path?  People should be able to recognize from the character of the area that it is a destination, not a through path, but when we engineers optimize roadway environments for the automobile, it becomes confusing.  If the land use is a destination, then people shouldn't be driving at 45 mph (or even 35mph) in front of it.  They shouldn't even want to drive that fast. 

We make believe that this isn't a big a problem if the only mode of travel is vehicular, but that really isn't ever the case.  People walk.  Stroads are the places where pedestrians get killed most often.  It may not be many people, but walking people are vulnerable and engineers are ethically bound to protect vulnerable users, either by restricting them from the environment entirely (like with limited access highways) or by taking care to make sure they are adequately protected within the environment.  As engineers, we have protected the automobile users and encouraged the optimization of vehicular travel to the detriment of all other users.  It's not just us engineers--land use patterns are just as important and we land use planners need to be more rigorous about making a distinction between destinations and open spaces fit for paths.

That is going to need some rethinking or even some un-engineering. 

Thursday, July 5, 2012

Sometimes details matter

I came across this wonderful blog post this morning about lovely details that support dynamic placemaking.  He included simple things like window boxes, art, decorative doors, little gardens, fountains, seating, courtyards, pocket parks and historic preservation.
Withers-Maguire House, Ocoee, FL

I will take issue with his argument that only authentic historic architecture is valuable--For us here in Central Florida, we don't really have anything substantially authentic other than the beautiful cracker houses and white victorian homes that are so well suited to our climate.  What we do have is people from all over the world who bring their architectural traditions here--and I love that.

From a community standpoint, I would add Farmer's markets and local festivals as time oriented placemaking.

Friday, June 29, 2012

Park Libraries in Columbia

I absolutely love this idea.  When I first saw this, I thought it was a bus stop.  It's not, but it probably should be. 

It's a portable park based library in Columbia.  They have about 100 around the country to encourage literacy.  Each are staffed with a worker who receives a small stipend.  It wouldn't be hard to redo these as library vending machines in urban locations.  It would make waiting for the bus much more relaxing and attractive. 

Saturday, February 4, 2012

Creative Placemaking of a Different Kind


The New Ideal?
I'm not sure urban designers really can create what most planners think of as a "creative place," or whether we even should.  It is the people that gather that provide the creative energy, not the place.  The best urban designers can do is create physical enviornments that are supportive and pleasant for the invisible community of relationships that already exists.  When you go about trying to create a "creative place," I have a feeling that you're just as likely to get bums off the street as you are creative geniuses--and I'm not always sure you can tell the difference.  Is that not why La Boheme is so enraptured with lightly employed, starving young people?

Frankly, I'm somewhat skeptical about the whole Richard Florida "Creative Class" concept anyway.  Bohemians may bring a certain amount of heat, but are not likely to have the kind of wisdom and experience that brings light.  If you really want to see economic development and benefits that span across wide levels of society, it is the entrepreneurs, engineers, medical researchers and non-profits that you want to support, and they often like suburbs.  Teaching them to enjoy walkable enviornments will help them synergize and cooperate, but there's a limit to how many relationships they can support and remain productive.  That's why they tend to prefer lower densities. 

Winter Garden Farmer's Market
I have to say I feel uncomfortable in environments that are dense enough to require that I intentionally ignore huge swaths of the people around me.  The farmer's market in Winter Garden's walkable downtown is great because I recognize so many of the people there.  Around 11:00am when the crowds are at their thickest, I don't enjoy it nearly as much.  Our little farmers market is, to me, placemaking at its best.  It is a third place where the entire community gathers at the same time and place.  We have events in the downtown about every other month too.  The relationships that are built and supported there are  joined by loose cultural institutions, like church, school, club and community fitness classes.  We know each other.  We work together.  When life happens, we do fund raisers for each other.  Is the strength of the community based on the streetscaping we did 7 years ago or the farmer's market pavilion we built last year?  No, but they provide a supporting framework for us to grow and strengthen the relationships we already have.  They also provide a place for newcomers to begin to integrate into the existing cultural fabric.  We had a community before we had a streetscape.  The streetscape just allows a larger group of people within the city to join us. 

RR Depot, Circa 1915
Many of the elders in our community have been quoted to say, "The good old days never looked this good."  That's true.  A century ago, our downtown was a thriving industrial marketplace focused on the rail service that got the agricultural products of our community to the marketplace.  It was messy.  It was coal powered steam engines, migrant workers and citrus barons.  It was city-wide fires and rebuilding in brick.  It was big bass fishing, hotels and a trailer city for snow-bird fishermen.  The times inbetween have not always been comfortable.  Pollution from the industrial scale agriculture killed the fish in the lake.  It became more profitable to plant Yankees than oranges when the cost of kerosine became too high to protect the groves from the few freeze days that inevitably come each year. 

Scoops Ice Cream Shop
Industrial citrus production has changed to information industries, hydroponics and telecommunications.  Our community is no longer the center of activity but a tertiary piece of a larger region but we do not make relationships on a regional scale, and our community is good at knitting lives together locally.  We don't have a single driving industry--we support industries all over the region.  We do have significant talent brought to the area through Disney and several of these talented chefs have chosen our downtown to open their own private places, like the French Pastry chef from Paris whose kids go to school with my own or the former executive that runs the ice cream shop and knows my daughter by name.   The downtown revitalization provided a venue for these valuable members of our community to use their substantial talents for local benefit and we love to support them.  We have a higher than average number of advertising and graphic arts firms, so I guess we are "creative" after all. 

Winter Garden has become a "place" in a creative and encouraging way.  That to me is creative placemaking...