Efficiency – every engineer’s favorite word. It’s perhaps the most important criterion to differentiate good engineering designs from bad ones.
How is efficiency measured in transit systems? One metric often used is the cost per vehicle revenue mile. A vehicle revenue mile (VRM) is the distance that a vehicle travels while in revenue service. In other words, if a train is in service collecting fares, the distance it travels counts towards the VRM. You can think of the amount of VRMs as the amount of service being provided. The cost per VRM is simply the operating costs divided by the number of VRMs. More efficient systems will be able to provide more service at a lower cost.
Another metric used is the cost per unlinked passenger trip, which can be thought of as the cost per rider.
With these two metrics in mind, I evaluated 17 cities to see which systems were more efficient than the others. I assessed these systems using 2014 data, which is the most recent data published by the NTD. You can see the results in the chart below. 
The vertical and horizontal lines represent the average values based on this sample. The average cost per VRM is $16.62 and the average cost per rider is $4.32. Cities in the bottom-left corner (highlighted in green) are below average on both metrics, and thus are considered efficient systems by comparison. Systems in the upper-right corner (indicated in red) are the exact opposite, they have costs that are above average and are less efficient. Of course, these metrics don’t tell everything, but they serve as a good starting point to help categorize successful systems from failures.
Moving beyond efficiency, another consideration is the productivity or effectiveness of a transit system. One way to look at this is by evaluating the number of unlinked passenger trips per VRM. This, in a way, shows how many people a system is moving. For this evaluation, I ranked the cities from the highest trips per VRM to the lowest. I also indicated the year that service began in each city. The hypothesis is that older light rail systems will do better than older systems. Why? – Economics.
If we think of transit service like any other good/service, then there are certain places where there is a better market for it than others. You would build your first store in the best location to maximize profit. If you open a second store you would place it in the second best location, and so on. The theory is that the best cities in the United States for light rail transit built it already. The more recent projects from 2000 onward are in less desirable markets. If this is true, we should see the older systems at the top of the rankings and newer projects towards the bottom. The results are shown in the graph below. 
- The color scheme is as follows:
- Systems opened on or before 1995: Green
- Systems opened between 1996-2000: Blue
Systems opened between 2001-2005: Purple
Systems opened between 2006-2010: Orange
Immediately it seems that the old vs. new theory does not hold up. The best system is Houston which began light rail service in 2004. There appears to be a good mix of newer and older systems across the rankings. While this does not necessarily discount the hypothesis completely, it does suggest that the age of a system may not play as much of a role in its productivity and efficiency. Going forward I want to explore this some more and try to find out, if not age, what characteristics DO impact performance.