Day: 2008-07-28

A Theory of Modes

| David Levinson

Wikipedia’s article List of transport topics gives a list of a variety of modes largely defined by their technology (are they powered by animals or engines, are the engines on the vehicle or is the vehicle powered by a cable, do the vehicles travel on land, sea, or water, etc. While this is a reasonably comprehensive list and a reasonable organization of the subject for wikipedia, it does not really get at the transportation aspect of modes, focusing instead on their mechanical aspects.
I propose a schema that classifies passenger modes according to how they operate, not how they are paid for or what technology is employed:
The key attributes are:
* Availability (can you travel on demand, is a vehicle easily hailed, or is a reservation required?),
* Accompaniment (can your party travel alone, or is the ride shared with others?),
* Fixity of route ends (are the origin and destination of the route fixed?),
* Fixity of route stops (are the stops fixed, or does the vehicle stop anywhere between the origin and destination?),
* Fixity of schedule (does the vehicle adhere to a schedule?),
* Driver (does the party drive itself or rely on others?).
In this way, we can see the similarity or differences of seemingly different or similar modes.

Accompaniment Route Ends Driver Stops Schedule Example
On-demand          
Own Party Variable Self Variable Variable Car
          Motorcycle
          Bicycle
          Walking
          Carpool
           
  Variable Other Variable Variable Taxi
  Fixed Other Variable Variable PRT
           
Shared Variable Other Variable Variable Shared Taxi
  One end fixed Other Variable Variable Airport Express, Hotel Van
           
  Two ends fixed Other Variable Variable Jitney
    Other   Fixed Schedule Bus
    Other Fixed Stops Variable Elevator, People Mover
    Other   Fixed Schedule Rail, BRT
    Other Nonstop Variable Stagecoach
          Express Bus/Train
By reservation         Airline
Own Party Variable ends Self     Limosine
    Other     Car Share, Car Rental
Shared Variable ends       Paratransit

Evaluation of the Transportation Effects of the I-35W Bridge Collapse

| David Levinson

The Nexus group webpage bringing together our ongoing and completed research on the I-35W Bridge collapse is available here. Evaluation of the Transportation Effects of the I-35W Collapse
Note in particular, several reports (links near the bottom of the page) which document the effects of the bridge collapse, reproduced here:

Zhu, S, D. Levinson, H. Liu, and K. Harder (2008) The traffic and behavioral effects of the I-35W Mississippi River bridge collapse (under review)

Xie, F. and D. Levinson (2008) Evaluating the Effects of I-35W Bridge Collapse on Road-Users in the Twin Cities Metropolitan Region (under review)

He, Xiaozheng, Saif Jabari, and Henry X. Liu (2008) Modeling Day-to-day Trip Choice Evolution under Network Disruption (under review)

The Launch of JTLU

| David Levinson

One week ago we announced to the world the availability of the first issue of Journal of Transport and Land Use.
In that week (July 20-26) we had 1929 visits to the site, including 6121 page views. Of those visitors, 75% were new, meaning the other 25% had visited the site previously.
Visitors came to the site from 56 different countries and every US state except Wyoming, Alabama, and Rhode Island.
Just to see how quickly people read email, the vast majority of announcement emails were sent last Monday (though after work Monday in about half the world). Most people visited on Monday or Tuesday
July 21, 712
July 22, 629
July 23, 310
July 24, 161
July 25, 83
July 26, 15
July 27, 22
which forms a very nice survival curve.
Prior to the announcement, the site was averaging 10 to 20 hits per day at random (about half of which were University of Minnesota staff futzing with the site).
Even more interesting, 613 people are now registered on http://www.jtlu.org, up from just over 200 before we launched, so another 400 people decided JTLU was interesting enough to be notified of future issues.

Bridge over I-35E begins to crumble

| David Levinson

From Strib: Weather, age eroded 35E bridge
“The 6-foot-by-9-foot-by-1-inch patch that peeled off could be described as a veneer for the underside of the steel beams that span the length of the bridge and support it, Dorgan said. Those beams are structurally unaffected by the loss of concrete, he said.”
If the aesthetics (i.e. veneer) distract from function (that is, it falls on cars), perhaps bridges should be strictly functional.