[jmecklenborg]

Originally Posted by ardecila

This is a common misconception. The weight on LRT vs HRT is comparable. We're not talking about mainline rail stock (and even those can be much lighter with new FRA rules). "Light rail" was coined in the 1960s at the same time as the first light cola and diet foods. It had nothing to do with train weight, it just referred to the ability of the technology to be built with at-grade sections, shorter trains, and smaller stations. "Heavy rail" appears to have been coined after "light rail" to refer to the older style of subway and metro systems.

-Metro's Breda A650 stock on the HRT Red/Purple Lines is 80,000lbs per single car and 75' long, so 1066 pounds per linear foot or 20,000lbs per axle. Metro's Kinkisharyo P3010 stock for LRT lines is 99,000lbs per articulated car and 89' long, so 1112 pounds per linear foot or 16,500 lbs per axle.

So a train of equivalent length in LRT is actually the same or heavier than HRT, but the axle loading is a little less because there are more axles.

When it comes to designing aerial structures and viaducts, there's no reason an HRT elevated structure needs to be any different from an LRT elevated structure. The only exception (and this is specific to LA, not a general rule) would be the stations, because the HRT trains in LA are longer so the stations would also need to be longer unless you want to restrict train length.

They are more similar than most HRT/LRT comparisons because the Los Angeles LRT system is not low-platform (like newer systems in Seattle, Phoenix, etc). However, the Breda HRT subway cars are 10 feet wide whereas the LRVs are about 8.5 feet wide, which makes a huge difference in the potential load from standing passengers.