Transportation Modeling Books to Read

December 17th, 2013

This is a two-part post.  The first part are books that I've read that I think are really important to the modeling community.  These books are important for the development

Recommended Items

A Self-Instructing Course in Mode Choice Models. Frank Koppelman and Chandra Bhat
This is an excellent resource to self-teach multinomial and nested logit modeling. It comes with many examples (a few of which I have discussed here) and talks about many of the tests and metrics that are important to good model formulation and evaluation.

Travel Model Validation and Reasonability Checking Manual. TMIP.
This is a great resource of validation checking and what to look for in regards to reasonableness checking.

Special Report 288: Metropolitan Travel Forecasting: Current Practice and Future Direction. TRB.
This is a critical look at many of the modeling techniques we hold dear to our hearts.  I've been tempted to re-read it and see if things are a little better now that it has been over 5 years since it was released.

Kenneth Train's Website (thanks to Krishnan Viswanathan).  It didn't dawn on me that this should be part of this list, but it should.  I've seen his website (and maybe even linked to it previously) while working on multinomial and nested logit modeling with R.  His website is a treasure trove of discrete choice analysis

On My To-Read List

"Hubris or humility? Accuracy issues for the next 50 years of travel demand modeling". David Hartgen. Transportation volume 40 issue 6.

Computational and Mathematical Modeling in the Social Sciences. Scott de Marchi.

Calibration of Trip Distribution Models by Generalized Linear Models. John Shrewsbury, University of Canterbury.

Megaprojects and Risk: An Anatomy of Ambition. Bent Flyvbjerg, Nils Bruzelius, Werner Rothengatter.

 

Recommended

Am I missing any?  Add a recommendation in the comments.

Tour-Based Modeling: Why is it Important?

June 12th, 2010

One thing that is constantly bounced around is why tour-based modeling is better than trip based modeling.  We've been using trip based modeling for 50 years, isn't it timeless?

No.

Fifty years ago, when the trip based modeling methodologies were developed, the primary reason was to evaluate highway improvements.  While tolling was in use, the bonding requirements were likely different.  Transit, while extremely important, was not in the public realm (the streetcars were normally privately owned by the area's electric company).

Now, there are a lot of demands on travel models:

  • Tolling/Toll Road analysis at a better level
  • Different tolling schemes (area tolling, cordon tolling)
  • Travel Demand Management (telecommuting, flex hours, flex time, alternative schedules)
  • Better freight modeling (which now is becoming commodity flow and commercial vehicle modeling)
  • Varying levels of transit (local bus, express bus, intercity bus, BRT, light rail, and commuter rail

While many of these can be done with trip based models, most of them cannot be done well with trip based models.  There are a number of reasons, but the few that come to mind are aggregation bias, modal inconsistency, and household interrelationships.

Aggregation Bias

Aggregation bias occurs when averages are used to determine an outcome.  For example, using a zonal average vehicles per household, you miss the components that form the average, such as:

20 households, average VPHH = 2.2
2 HH VPHH = 0
5 HH VPHH = 1
4 HH VPHH = 2
6 HH VPHH = 3
3 HH VPHH = 4+

The trip generation and modal choices (car, bus, bike, walk, etc.) among these households are all different, and are even more more different if you look at the number of workers per household.

Modal Inconsistency

In trip based modeling, "people" are not tracked throughout their day.  So, if someone rides the bus to work, there is nothing in the model to ensure that they don't drive from work to get lunch.  While we don't want to force people to use the same mode, since many people will use the bus to get to work and then walk to lunch or to go shopping during lunch, we want to make sure that there is some compatibility of modes.

Household Interrelationships

One of the features of of tour based models is determining each person's daily activity pattern.  During this process, certain person types can determine what another person is doing.  For example, if a preschool age child is staying home, an adult (whether they are a worker or not) HAS to stay home.  Another example is if a school-non-driving-age child is going on a non-mandatory trip, an adult must accompany them.  Trip based models don't know about the household makeup and the household interaction.

The above are only three of the many reasons why tour-based modeling is important.  There are many more, but I feel these are some of the most important and some of the easiest to understand.

What are those little green boxes???

April 11th, 2009

It is the start of traffic counting season in Ohio. Each year, we get about 7 months to count the cars on the road. With my involvement in this type of work, I hear a lot of horror stories. First off, I wanted to discuss how these things work and how the data is used and cannot be used, and then show some of the war stories.

Traffic Counter on side of road

Traffic Counter on side of road

First off: how these things work

Those that have been around for 30 or more years may remember when some gas stations had a hose that rang a bell to call a station attendant to pump your fuel. Those that don't should watch Back to the Future. This is the same basic concept for most traffic counters. There are hoses that go across the road, and based on what the sensors feel and the time between them, these little green (or sometimes gray) boxes calculate the number of axles, distance between them (which can be used to derive the type of vehicle), and the speed.

I know that speed is a big issue with a lot of people. After all, some of these counters are being used for speed studies to see if they want to put a cop on a road at a certain time. This does happen, despite my wishes that cops and others would use less-detectable methods for enforcement. There are two other ways that counts, with speed, can be taken. One is by RADAR (the same thing they use for active speed enforcement). Mind you, for speed sampling, RADAR is pretty useful when installed correctly, and the boxes can be hidden quite well. The other is using magnetic loops. There are portable models of these that sit in the lane and are difficult to see (and also susceptible to theft). There are also permanent models that can be completely hidden from view.

One thing I can say with ALL hose counters: WE CANNOT USE THEM FOR SPEED ENFORCEMENT! The units do not have any cameras (etc), so if you speed while going over them, we know you did, but we don't know who you are!

Second off: How We Use The Data We Get From These Things

This one differs by jurisdiction, but most use it for traffic studies. Speed, count, and vehicle type are very useful for roadway improvement design. Another use is for travel model validation. We (specifically me, since it is my job) use this to ensure that the region's travel model is accurate so when we use it to plan billions of dollars in improvements, we know we're not just guessing, which would be a waste of money.

Law enforcement will use the number of speeders per unit of time to plan when to run patrols. As I indicated, I wish they wouldn't use hose counters for this, but they do, and the data they get is accurate. However, hoses are pretty conspicuous, which is why I wish they wouldn't use them.

We cannot use the data in court. You cannot be detected to be going 45 MPH in a 25 MPH zone based on a traffic counter. The counters do not have cameras in them, and none that I know of can connect to a camera. A camera would be required to prove who was speeding. Without the connection, it would be difficult to prove, since the times would have to be the same, the counter has to be operating perfectly, and the hoses have to be measured very precisely. Some states also forbid the use of cameras for passive law enforcement (a cop can actively use a RADAR+camera, but not mount one on a pole and get every car that is speeding).

The War Stories

I have two, both given to me by a salesperson for Jamar Tech, one of the leading traffic counter manufacturers.

City of Boston Thinks a Counter is a Bomb. This one is proof that some cops don't use hose counters, else they would have known what this unit is.

Counter burned, likely by an accelerant. PDF from Jamar, which the salesperson sent me just after I bought 8 counters from him.

Don't Mess With Them!

It amazes me that 1 month into the season, I've had to replace several hoses because of cut or stolen hoses. This is your tax dollars at work. The more hoses we have to replace, the less money we have to improve the roads.