Cabintaxi's Experience with Sub-second Headways
by Marsden Burger
It is important to realize that Cabintaxi is the only short headway system that is known to have been actually run at 0.5 second separations (headways) between vehicles. [Separations are important because the term headways refers to the time between the nose of one vehicle and the nose of the second trailing vehicle. Separation is the tail to nose difference. Headways of .5 seconds are impossible if the vehicle body is 15 feet long like a 12 passenger Cabintaxi vehicle, but 5 second separations are possible. It also figures significantly into the brickwall stopping ability of three seconds or less.]
While it was operated on the test track at 0.5 second separations at times to see how the system preformed, it was never planned to operate at these short headways, and would have required extensive testing to consider what changes may have been needed to prepare for this style of operation. Its development was based on the understanding that its operational scenario would require the ability to provide a safe "brickwall" stop. Therefore, design requirements for sub-second separation operation were never carried out. Endurance testing at 0.5 seconds was never a part of the program, and endurance testing is critical to really know if a design concept works.
Extensive testing was never carried out with the goal of showing that 0.5 second separations would be acceptable for public transit applications of the Cabintaxi technology. There is though, no reason to think that Cabintaxi could not be capable of doing 0.5 second separations if they were considered desirable and necessary in particular applications. However, without a test track to accomplish large-scale endurance testing, a gradual evolutionary process would be the only responsible way attain this level of operational safely.
The value of a system that can provide safe and reliable 3-second headway operation is enormous compared to existing public transit systems. For many reasons, it is harder to develop a system that can provide a safe brick-wall stop under 3 seconds than a system operated without the "brick-wall stop" requirement. Cabintaxi was able to accomplish the 3-second brick-wall stop on a test track.. Evolving into a system that is able to operate at sub-second separations is mostly likely to be the best way to achieve suitably safe operations using 0.5 second separations.
For additional detail on this important capacity and safety issue, contact Marsden Burger President, Cabintaxi Corporation, 1703 Parker, Detroit, MI 48214; Ph: 313-921-3955, e-mail: firstname.lastname@example.org
Last modified: February 21, 2008