be meaningful in a small vehicle PRT mode. The larger cars could also be connected front-to-back to form two-car trains, further increasing capacity for some simple applications. One problem with all elevated transportation system structures in general, is that the guideways (highways or transit) are widely considered to be an eyesore. In order to reduce the size of the guideways, Cabinentaxi took the uncommon approach of optionally allowing its cars to run on the top or bottom of a single track. The cars could not be switched from top to bottom, however. If this option was used, the guideways were supported on pillars that attached to the track from the side, rather than directly below. Cabinentaxi's guideway is noticeably smaller and thinner than conventional elevated systems, like the Vancouver SkyTrain. The track is approximately six feet wide, slightly smaller than a row of parking spots on the side of a city street. Prototypes and testing Testing of the motor and control systems started in 1972 on a 13-meter closed-loop track, running for 18 months. This was followed in August 1973 by a 150 meter test track and three 3-passenger vehicles installed near Hagen, Germany. The test track was expanded several times. By October 1974 it was 1136 meters long and featured two passenger stations with a closed-loop track, adding two additional vehicles for a total of five. By 1975 it had three stations and nine vehicles. The first 12-person vehicle was introduced that October. The final expansion was completed in 1976, bringing the total track to 1.9 km with six stations and twenty-four vehicles. In 1975, Raytheon Missile Systems examined the prototype system and decided to license it for deployment in the U.S., but a final agreement was never reached. Cabinentaxi technology logged over 400,000 vehicle-miles between 1975 and 1978 on the Hagen test track. In 1977 the system completed fleet operation endurance testing of 7500 continuous vehicle hours, extending that in 1978 to 10,000 continuous vehicle hours. These are the only PRT fleet endurance test of these magnitudes ever carried out. Headways were reduced throughout the period, vehicle separations started at under 3 seconds, reaching 1.9 seconds in later tests, about the same as cars on a highway. The basic operating speed was also increased during testing, from the original 30 km/h to 36 in the later tests, with options for even higher speeds in production versions. Late in