Is there a need for a standard connection? Most transit agencies that operate light rail either have a homogenous fleet, or if they do have mixed fleets, they either are similar enough to interoperate, or they suck it up and keep them separate. Also, it can be argued that orders for light rail vehicles as a whole are not frequent, so having a standard might be moot as technology improves quickly. The MBTA is no exception. The Type 7s were not able to trainline with the Boeings, which were also not able to trainline with PCCs. The MBTA had to get the T7s and T8s to trainline because they weren't replacing the entire T7 fleet with T8s, and thus needed a solution for ADA purposes. (the latter order of T7s, the 3700s, were relatively new when the T8s were ordered. The T8s were delayed and ended up being lemons which meant that it would have been foolish to order more)
bostontrainguy wrote:CRail wrote:That's correct. What the T was looking for with the Type 9 order was basically reliable Type 8s. The fact that they will not trainline with them is insane to me, though.
Trying to get the Japanese speaking Type 7 to talk to the Italian speaking Type 8 was difficult enough. Now trying to throw in a Spanish speaking third version probably can't be easily done. They won't run together, but they will be able to physically couple if necessary.
The Type 7 is nearly analog, as in very little to no computer control at all. The Type 8s were very computerized, so all they did was slap in the Type 8's computer onto the Type 7s, and coupled them together. It was a very rudimentary trainlining at best. The differences in acceleration and deceleration curves probably caused excess wear on both fleet types. Based on my observations as a passenger, it appears that they fixed the problem by rebuilding the T7s, and adjusting the T8s so that the propulsion system cuts out and coasts at lower speeds to prevent conflict (but can cause wheelslip for the T7 as it is dragging/pushing the dead weight of a T8). The T8's computer systems are probably very old/outdated by today's standards.
The Type 9s (I am assuming) have the innards of the CAF Urbos 3 platform, so they're more modern than the 7s and 8s, which might be why they can't trainline. It wouldn't make financial sense to re-do the entire T7 and T8 fleet to upgrade the computer to allow trainlining for the very few T9s.